Gold - Complete User Guide

Gold is a small IBM Power5 system consisting of one front-end node and one compute node. The compute node is a Dual-Processor 1.5 GHz Dual-Core Power5 520 with 8 GB of RAM. This system is designed to be used only by users who have legacy IBM architecture-optimized or AIX-specific code. Gold is to help facilitate the porting of any code designed for the IBM SP system at Purdue, which was retired in 2008.

Detailed Hardware Specification

Number of Nodes	Processor	Cores per Node	Memory per Node	TeraFlops
1	Dual-Processor 1.5 GHz Dual-Core Power5 520	4	8 GB	0.024

Gold runs AIX 5.3 and uses PBSPro 9.x for resource and job management. Operating system patches are applied monthly or as security needs dictate. All nodes have been configured to allow for unlimited stack usage, as well as unlimited core dump size (though disk space and server quotas may still be a limiting factor).

Obtaining an Account

Accounts are granted on Gold only to Purdue faculty and staff with a need to work on IBM SP (AIX) architecture-specific code. If you have such a need, you may request access to Gold using the online Research Computing Account Request Form.

Login / SSH

To issue jobs on Gold, users may log on to the front-end host gold.rcac.purdue.edu via SSH.

SSH Client Software

All access to the RCAC systems must be through secure (encrypted) connections. Standard telnet and FTP are not supported. SSH, SCP, and SFTP may be used instead.

Secure Shell or SSH is a way of establishing a secure channel between a local and a remote computer. It uses public-key cryptography to authenticate the remote computer and (optionally) to allow the remote computer to authenticate the user. It is usually used to log in to a remote machine and execute commands similar to telnet, but it also supports tunneling and forwarding of X11 or arbitrary TCP connections. The associated SFTP and SCP protocols may be used to transfer files. There are many SSH clients available, depending on the operating system you use.

Linux / Solaris / AIX / HP-UX / Unix:

"ssh", "sftp", and "scp" are pre-installed. Log in using ssh myusername@servername.

Microsoft Windows:

PuTTY is an extremely small download and includes free SSH, SCP, and SFTP clients.
Secure CRT (SSH client) and Secure FX (SFTP client) are commercial clients which are available free to Purdue students, faculty, and staff with a Purdue career account.

Mac OS X:

"ssh", "sftp", and "scp" are pre-installed. You may start a local terminal window from "Applications->Utilities". Log in using ssh myusername@servername.
MacSSH and MacSFTP
NiftyTelnet 1.1 SSH

SSH Keys

SSH can be used in conjunction with many different means of authentication. One popular authentication method is called Public Key Authentication (PKA). PKA is a method of establishing your identity to a remote computer using related sets of encryption data called keys. PKA is a more secure alternative to traditional password-based authentication with which you are probably familiar.

To employ PKA via SSH, you manually generate a keypair (also called SSH keys) in the location from where you wish to initiate a connection to a remote machine. This keypair consists of two text files, one which is called a private key and one which is called a public key. You keep the private key file confidential on your local machine or local home directory (hence the name "private" key). You then login to a remote machine (if possible) and append the corresponding public key text to the end of a specific file, or have a system administrator do so on your behalf. In future login attempts, the public and private keys are compared to verify your identity, which then grants you access to the remote machine.

As a user, you can create, maintain, and employ as many keypairs as you wish. If you connect to a computational resource from your work laptop, your work desktop, and your home desktop, you can create and employ keypairs on each. You can also create multiple keypairs on a single local machine to serve different purposes, such as establishing access to different remote machines, or establishing different types of access to a single remote machine. In short, PKA via SSH offers a secure but flexible means of identifying yourself to all kinds computational resources.

Passphrases and SSH Keys

When a you create a keypair, you are prompted to provide a passphrase for the private key. This passphrase is different than a password in a number of ways. First, a passphrase is, as the name implies, a phrase. It can include most types of characters, including spaces, and has no limits on length. Second, this passphrase is not transmitted to the remote machine for verification. It is used only to allow the use of your local private key and is specific to a specific local private key.

Perhaps you are wondering why you would need a private key passphrase at all when using PKA. If the private key is kept secure, why the need for a passphrase just to use it? Indeed, if the location of your private keys were always completely secure, a passphrase might not be needed. In reality, a number of situations could arise in which someone may improperly gain access to your private key files. In these situations, a passphrase offers another level of security for you, the user who created the keypair.

Think of the private key/passphrase combination as being analogous to your ATM card/PIN combination. The ATM card itself is the object that grants access to your important accounts, and as such, should be kept secure at all times—just as a private key should. But if you ever lose your wallet or your ATM card is stolen, you are glad that your PIN exists to offer you another level of protection. The same is true for a private key passphrase.

When you create a keypair, you should always provide a corresponding private key passphrase. For security purposes, avoid using phrases that would be guessed by automated programs (e.g. phrases that consist solely of words in English-language dictionaries). This passphrase can never be recovered if forgotten, so make note of it. There are only limited situations when the use of a non-passphrase-protected private key is warranted—conducting automated file backups is one such situation. If you need to use a non-passphrase-protected private key to conduct automated backups to Fortress, see the No-Passphrase SSH Keys section.

SSH X11 Forwarding

SSH supports tunneling of X11 (X-Windows). If you have an X11 server running on your local machine, you may use X11 applications on remote systems and have their graphical displays appear on your local machine. These X11 connections are tunneled and encrypted automatically by your SSH client. You will need to have a local X11 server running, but free and commercial X11 servers are available for various operating systems.

Linux / Solaris / AIX / HP-UX / Unix:

An X11 server is at the core of all graphical sessions. If you are logged in to a graphical environment on these operating systems, you are already running an X11 server.

Microsoft Windows:

Xming is a free X11 server available for all versions of Windows, although it may occasionally hang and require a restart. Download the "Public Domain Xming" or donate to the development for the newest version.
Hummingbird eXceed is a commercial X11 server available for all versions of Windows.
Cygwin is another free X11 server available for all versions of Windows. Download setup.exe and make sure you select the following packages which are not included by default:
```
	Packages from the X11 group:
	
	X-startup-scripts
	XFree86-lib-compat
	xorg-*
	xterm
	xwinwm
	lib-glitz-glx1
	
	Under the Graphics group, also select opengl, if you want OpenGL 
	support. 
```
Then when the Cygwin X server is installed, start an xterm and type: XWin -multiwindow in it and then enter. You can now run your SSH client.

Mac OS X:

X11 is available as an optional install on the Mac OS X v10.3 Panther and x10.4 Tiger install disks. Run the installer, select the X11 option, and follow the instructions.

Enabling the forwarding

Once you are running an X11 server, you will need to enable X11 forwarding/tunneling in your SSH client:

"ssh": X11 tunneling should be enabled by default. To be certain it is enabled, you may use "ssh -X".
PuTTY: Prior to connection, in your connection's options, under "Tunnels", check "Enable X11 forwarding", and save your connection.
Secure CRT: Right-click a saved connection, and select "Properties". Expand the "Connection" settings, then go to "Port Forwarding" -> "Remote/X11". Check "Forward X11 packets" and click "OK".

Note that SSH will set the remote environment variable $DISPLAY to "localhost:XX.YY" when this is working correctly. If you had previously set your $DISPLAY environment variable to your local IP or hostname, you must remove any set/export/setenv of this variable from your login scripts. The environment variable $DISPLAY must be left as SSH sets it, which is to a random local port address. Setting $DISPLAY to an IP or hostname will not work.

Passwords

If you have received a default password as part of the process of obtaining your account, you should change it immediately when you log on for the first time. This can be done from any terminal/SSH session with the command "passwd". You will have the same password on all RCAC systems. If you change your password on any one RCAC system, it will change on all RCAC systems.

If you already have a Purdue career account, then you will initially be given the same userid and password as your career account. There is no need to change your career account password because you have received an account on RCAC systems.

There is not currently any requirement regarding how often you must change your password within RCAC, but for security reasons changing a password every six months, preferably every three months, is good practice.

All passwords should:

Be something you have never used as a password before, on this or any other system.
Be easy for you to remember and difficult for others to guess.
Be at least eight characters long.
Be a combination of upper and lowercase letters, numbers, and symbols.
TIP: Abbreviate a sentence or song lyric: "The dog Samson ate 4 new slippers!" = "TdSa4ns!"

Never share your password with another user or make your password known to anyone else. Systems staff will NEVER ask for your password, by email or otherwise.

Email

There is no local mail delivery available on Gold. All email sent to Gold will be forwarded to mail.rcac.purdue.edu for delivery.

Login Shell

When your account is activated, your default shell will probably be set to tcsh—an enhanced version of the Berkeley UNIX C shell (csh). The tcsh shell is completely compatible with the standard csh, and all csh commands and scripts work unedited with tcsh. For more details on tcsh, enter "man tcsh" while logged in.

The other popular shell is GNU Bourne-Again SHell (bash), which is completely compatible with the Bourne shell (sh). For more details on bash, enter "man bash" while logged in.

To change your shell temporarily or to try out another shell, just type the shell name as a command ("bash", "tcsh", "ksh"). This will run the new shell as a subshell. To return to your original shell, simple type exit.

To permanently change your login shell, use the command chsh:

$ chsh -s bash
     (or)
$ chsh -s tcsh

To see a list of all available shells:

$ chsh -l

The next time you log on, you will start in the new shell. However, you may switch back at any time.

Storage Options

File storage options on RCAC systems include home directories, scratch file systems, /tmp, and long-term or permanent storage. Each of these have different performance and intended uses, and some vary from system to system as well. Home directories and long-term storage are backed up nightly, but scratch and /tmp are not and may be occasionally purged without warning. Below is more detail about each of these storage options.

Home Directories

Your home directory is the default directory you are placed in when you log in.

You should use this space for storing files you want to keep long term such as source code, scripts, input data sets, etc. It should also be used for files you want to keep and which you use often. The home directory will physically reside on the BlueArc NFS Server. You can find the path to your home directory by logging in, and typing pwd:

$ pwd
/home/ba01/u103/myusername

The second component of the reply indicates the name of the host where your home directory physically resides. In this example, the home directory is on the RCAC home directory file server named "ba01" under area "u103". This will vary from person to person. Remember, you can always check where your home directory is located by doing a pwd command in your home directory.

Regardless of its physical location, your home directory and its contents are available on almost all the RCAC front-end hosts and their nodes via the Network File System (NFS). The only exception is Black.

Note that your home directory has a quota capping the size and/or number of files you may store within. For more information, refer to the Storage Quotas / Limits Section.

Lost Home Directory File Recovery

Only files which have been backed up overnight can be recovered. If you lose a file the same day you created it, it can NOT be recovered.

Files Lost Less than Seven Days Ago

For files lost less than seven days ago, RCAC has implemented self-service file recovery. Backups of all your files are made at midnight daily and you may access these directly.

To recover files lost after midnight today (same day as loss):

$ set BACKUP=`echo $HOME | sed "s,/u1,_snap/backup_snap/u1,;s,/home/,/autohome/,"`
$ cd $BACKUP

  (now locate the file or directory you wish to recover within here)

$ cp mylostfile $HOME
  (or)
$ cp -r mylostdir $HOME

To recover files lost prior to today, but in last week (2-7 day loss):

  (set this to the date you lost the files: 4-digit year, 2-digit month, 2-digit day)
$ set DATE=YYYYMMDD

$ set BACKUP=`echo $HOME | sed "s,/u1,_snap/backup_snap_$DATE*/u1,;s,/home/,/autohome/,"`
$ cd $BACKUP

  (now locate the file or directory you wish to recover within here)

$ cp mylostfile $HOME
  (or)
$ cp -r mylostdir $HOME

Files Lost More than Seven Days Ago

For files lost more than seven days ago, you will need to request RCAC recover your files from backup tapes. Please do so using the flost command from the front-end host of an RCAC resource:

$ flost

Scratch Directories

Scratch directories are provided by RCAC and are intended for short-term file storage only.

Backups are not performed on scratch directories. In the event of a disk crash or file purge, files in scratch directories can not be recovered. Please be sure to copy any important files to more permanent storage.

All files stored in RCAC scratch directories older than 90 days will be automatically removed (purged). Owners of these files will be notified one week before removal via email. For more information, please refer to our Scratch File Purging Policy.

RCAC scratch directories are provided by a central BlueArc server and are accessible from most RCAC systems. There are two primary scratch file systems: scratch95 and scratch96. A scratch directory already exists for all Gold users. Your RCAC scratch directory is located under scratch95 or scratch96 within a subdirectory by the first letter of your username.

To find the path to your RCAC scratch directory, run myscratch:

	$ myscratch
	/scratch/scratch96/m/myusername

The variable $RCAC_SCRATCH is also set to your RCAC scratch directory path. Use this variable in any scripts. Your actual scratch directory path may change without warning, but this variable will remain current.

$ echo $RCAC_SCRATCH
/scratch/scratch96/m/myusername

To find the path to someone else's RCAC scratch directory, use the command findscratch:

$ findscratch someuser
/scratch/scratch95/s/someuser

Note that your RCAC scratch directory has a quota capping the size and/or number of files you may store within. For more information, refer to the Storage Quotas / Limits Section.

/tmp Directory

The /tmp directory is intended for temporary files that are used during the execution of a process or job or while you examine files created by your jobs. Used properly, /tmp may provide faster local storage to an active process than any other storage option. However, do not use it for longer-term storage or critical results.

Files stored in /tmp are not backed up and are removed whenever space is low or whenever the system is rebooted. In the event of a loss, files in /tmp can not be recovered, so use it only for files that can be recreated relatively easily.

Long-Term Storage

Long-term Storage or Permanent Storage is available to RCAC users on the DXUL/UniTree archival storage system, commonly referred to as "Fortress". DXUL (DiskXtender for Unix and Linux) and UniTree are a software package that manages a hierarchical storage system. Program files, data files and any other files which are not used often, but which must be saved, can be put in permanent storage. Fortress currently has a 1.2 PB capacity. However, since two copies are retained for every file, the usable capacity is only 600 TB.

Recently used files smaller than 0.5 MB have their primary copy stored on low-cost disks, but the second copy is on tape or optical disks. This provides a rapid restore time to the disk cache. However, the large latency to access a larger file (usually involving a copy from a tape cartridge) makes it unsuitable for use as active storage.

In addition to poor performance, these two uses can cause severe problems with the system itself:

DO NOT store any actively used files on Fortress.
DO NOT store large collections of small files on Fortress.

Do not use Fortress as a second home directory. Instead, use tar or some similar archive tool to combine all the smaller files you wish to store into a single large file first.

For active data storage you should use either local storage or a scratch file system. You may then copy any results you wish to archive to Fortress when computation is complete.

Fortress is directly accessible (via FTP, SSH, SCP, SFTP, and NFS) from all RCAC systems, as well as most systems in ECN and CS and from several other major servers on campus. To access Fortress in any way other than NFS, you must login to fortress.rcac.purdue.edu. RCAC has more information about Fortress, including how to obtain a Fortress account and how to access your files on Fortress.

Manual File Transfer to Long-Term Storage

There are a variety of ways to manually transfer files to your Fortress home directory for long-term storage.

SCP

You can use an SCP client to interactively transfer individual files and directories to Fortress. More information on SCP can be found in the File Transfer - SCP section of this guide.

SFTP

You can use an SFTP client to interactively transfer individual files and directories to Fortress. More information on SFTP can be found in the File Transfer - SFTP section of this guide.

Scripted File Transfer to Long-Term Storage

In the absence of NFS access to Fortress, you must login to fortress.rcac.purdue.edu to transfer files to long-term storage. There are limited situations where the use of a password or a passphrase-protected authentication keypair becomes impractical, and running scripted file backups to Fortress happens to be one of them. When you attempt to establish a connection to Fortress, you will literally be prompted to input a password or a local private key passphrase. Any time a script or automated process needs to establish the connection, it is unable to respond to such a request. To enable truly automated transfer of files to Fortress, you need to employ public key authentication via SSH with a non-passphrase-protected private key. For a conceptual overview of public key authentication, see the SSH Keys section of this guide.

Now, if your home directory is compromised and an attacker obtains your non-passphrase-protected private key, the attacker will be able to masquerade as you on machines that contain the corresponding public key. Luckily, certain usage restrictions can be customized for each keypair you employ. For example, you could create a non-passphrase-protected keypair and later specify that this public key shall only be used to run a file-backup script, and additionally, is only valid when connecting from a specific machine. Then, if the non-protected private key were to be compromised, the attacker would be saddened to realize that he could only run your file-backup script repeatedly.

It is very important to place a passphrase on all of your generated keypairs. Only use non-protected keypairs when absolutely necessary.

No-Passphrase SSH Keys

Here is how to set up a non-password-protected keypair for use with automated backup scripts to Fortress from Gold.

Log on to Gold
Create a non-passphrase-protected SSH keypair.

You should use this keypair for the sole purpose of automating backups on Fortress.

Specify your ~/.ssh/ directory and give the keypair a descriptive name (e.g. "bkup2fort_id_rsa") by using the "-f" flag:
```
$ ssh-keygen -t rsa -N "" -f ~/.ssh/mykeypairname
```
The ssh-keygen command should have created the following files:
```
$ ls ~/.ssh/mykey*
mykeypairname mykeypairname.pub
```
The first file is the private key. The second file is the public key counterpart.

Never distribute your private key or copy it to other machines.
Open the public key file with your favorite text editor and prepend the following text to restrict its use:
```
from="*.rcac.purdue.edu",no-port-forwarding,no-agent-forwarding,no-X11-forwarding,no-pty
```
This tells SSH to only allow connections from RCAC resources, to disable a number of forwarding functions, and to not allow interactive shell commands, respectively.

Copy your modified public key over to your Fortress home directory:

$ scp ~/.ssh/mykeypairname.pub myusername@fortress.rcac.purdue.edu:~/

Log into Fortress and cd to ~/.ssh. Create the ~/.ssh directory if neccessary:
```
$ ssh myusername@fortress.rcac.purdue.edu
$ cd ~/.ssh/
```
If a file named "authorized_keys" exists in the .ssh directory, set the proper permissions for it:
```
$ chmod 600 ~/.ssh/authorized_keys
```
If it does not exist, create it:
```
$ touch ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
```
Append your modifed public key to the "authorized_keys" file in your Fortress ~/.ssh directory:
```
$ cat ~/mykeypairname.pub >> ~/.ssh/authorized_keys
```

View your "authorized_keys" file. The last entry should look similar to this:

$ cat ~/.ssh/authorized_keys

from="*.rcac.purdue.edu",no-port-forwarding,no-agent-forwarding,no-X11-forwarding,
no-pty ssh-rsa AABBB3NzaC1yc2EABBABIwAAAIEA3SXgmvos4jFLVFLRrh6YrN3s8FuBOUTCJ0NIsc+
FtFrSGD2bVV6yMCgpdgz9RZS7U5uTJOW2VBWsJSb6cjjnA2WJzDcS0bEU3lw+TJszv2sEfl/CwF6dyj2U2
k5VrXIpdosZVKyjoqzQXhFicIRv1/ykdO8xp+qcgc09NbcyGhs= myusername@resource.rcac.purdue.edu

Delete your public key file on Fortress (it's now stored in the "authorized_keys" file):
```
$ rm ~/mykeypairname.pub
```
Log out of Fortress:
```
$ exit
```

SCP

If you have followed the instructions in the No-Passphrase SSH Keys section to employ an unprotected SSH keypair between Gold and Fortress, you can automate the backup process using backup scripts. Because of the restrictions you placed upon the public key, you cannot use this keypair to log on to an interactive SSH session on Fortress, but you can use it to send files from your Gold home directory to Fortress via SCP, or to run local scripts that employ SCP.

Since you can have multiple private keys on Gold (and a similarly, multiple public keys in any given "authorized_keys" file on Fortress), you always need to specify which keypair you intend to employ for a log-in attempt to Fortress. The most consistent way to do this is with SSH's "-o" flag. This passes options to configure SSH and can be used with all programs that use SSH for providing a secure connection (e.g. SCP, SFTP, and RSYNC).

To test automated SCP authentication from Gold to Fortress, use the following command:

$ scp -o IdentityFile=~/.ssh/mykeypairname ./mylocalfile myusername@fortress.rcac.purdue.edu:~/myremotefile

If this works (i.e. you are not prompted for a passphrase or login password), you can move on to implementing a script using SCP commands like the one above.

While only you can ultimately decide the best approach for your automated backup process, the example scripts below show, in general, how to employ backup scripts on Gold using SCP commands and public key authentication via SSH. The following bash script, named "fortress_backup_script_scp", uses SCP to recursively copy two directories on a user's Gold home directory to the user's Fortress home directory:

#!/usr/local/bin/bash

# A script to use SCP to copy
# whole directories to Fortress

# Define some parameters

user=myusername
remotehost=fortress.rcac.purdue.edu
idfile=~/.ssh/mykeypairname

# Manually populate an array of directories on the 
# local machine we wish to back up on Fortress

localdir[0]=~/mydir2backup
localdir[1]=~/mydir2backup_also

# Get the number of directories to be backed up

numdirs=${#localdir[*]}
count=1

# Loop over every entry in the "localdir" array to
# copy each directory recursively to a folder of 
# the same name in our home directory on Fortress.

printf "\n>> Starting Secure Copy backup to Fortress\n"

for dir in "${localdir[@]}"
do
  printf ">> Copying directory $dir to Fortress ($count of $numdirs)\n"
  scp -r -o IdentityFile=$idfile $dir $user@$remotehost:~/
  let count++
done

printf ">> Done...\n\n"

The output for this script is as follows:

$ ./fortress_backup_script_scp
 
>> Starting Secure Copy backup to Fortress
>> Copying directory /home/ba01/u100/myusername/mydir2backup to Fortress (1 of 2)
bigfile2.tar.gz                                100%  121MB  30.3MB/s   00:04    
bigfile1.tar.gz                                100%  121MB  40.5MB/s   00:03    
>> Copying directory /home/ba01/u100/myusername/mydir2backup_also to Fortress (2 of 2)
bigfile4.tar.gz                                100%  121MB  40.5MB/s   00:03    
bigfile3.tar.gz                                100%  121MB  40.5MB/s   00:03  
>> Done...

By using these techniques, you can automate your file backups to Fortress safely and efficiently.

SFTP

Since you can have multiple private keys on Gold (and similarly, multiple public keys in any given "authorized_keys" file on Fortress), you always need to specify which keypair you intend to employ for a log-in attempt to Fortress. The most consistent way to do this is with SSH's "-o" flag. This passes options to configure SSH and can be used with all programs that use SSH for providing a secure connection (e.g. SCP, SFTP, and RSYNC).

To test automated SFTP authentication from Gold to Fortress, use the following command:

$ sftp -o IdentityFile=~/.ssh/mykeypairname myusername@fortress.rcac.purdue.edu
sftp> bye
$

If this works (i.e. you are not prompted for a passphrase or login password), you can move on to implementing a script using SFTP commands like the one above.

While only you can ultimately decide the best approach for your automated backup process, the example scripts below show, in general, how to employ backup scripts on Gold using SFTP commands and public key authentication via SSH. The following bash script, named "fortress_backup_script_sftp", uses SFTP commands to navigate through Fortress directories, and pushes files from the user's Gold home directory when needed.

#!/usr/local/bin/bash

# A script to use SFTP to push files to 
# Fortress for backup.

# Set up some parameters

user=myusername
remotehost=fortress.rcac.purdue.edu
idfile=~/.ssh/mykeypairname

printf "\n>> Starting Secure FTP backup session to Fortress\n"

# Invoke SFTP mode, specifying the correct private key, 
# and forcing batch file input from a "here-document"
# (i.e. the rest of this script).

sftp -o IdentityFile=$idfile -b - $user@$remotehost << EOF

cd ./mydir2backup
lcd ./mydir2backup

put -P ./bigfile1.tar.gz 
put -P ./bigfile2.tar.gz 

cd ../mydir2backup_also
lcd ../mydir2backup_also

put -P ./bigfile3.tar.gz 
put -P ./bigfile4.tar.gz 

bye
EOF

# Now we are back to the bash shell...

printf ">> Done...\n\n"

The output for this script is as follows:

$ ./fortress_backup_script_sftp

>> Starting Secure FTP backup session to Fortress
sftp> 
sftp> cd ./files2backup
sftp> lcd ./files2backup
sftp> 
sftp> put -P ./bigfile1.tar.gz 
Uploading ./bigfile1.tar.gz to /archive/fortress/home/myusername/mydir2backup/bigfile1.tar.gz
sftp> put -P ./bigfile2.tar.gz 
Uploading ./bigfile2.tar.gz to /archive/fortress/home/myusername/mydir2backup/bigfile2.tar.gz
sftp> 
sftp> cd ../files2backup_also
sftp> lcd ../files2backup_also
sftp> 
sftp> put -P ./bigfile3.tar.gz 
Uploading ./bigfile3.tar.gz to /archive/fortress/home/myusername/mydir2backup_also/bigfile3.tar.gz
sftp> put -P ./bigfile4.tar.gz 
Uploading ./bigfile4.tar.gz to /archive/fortress/home/myusername/mydir2backup_also/bigfile4.tar.gz
sftp> 
sftp> bye
>> Done...

$

By using these techniques, you can automate your file backups to Fortress safely and efficiently.

Environment Variables

There are many environment variables related to storage locations and paths which are automatically set for you upon log-in, or may be changed if necessary. In addition, many more environment variables are set for specific applications, such as compilers, when "modules" for these applications are loaded. (See the module command section for more information.)

Use environment variables instead of actual paths whenever possible to avoid problems if the specific paths to any of these change. Some of the environment variables you should have are:

$USER: your username
$HOME: path to your home directory
$PWD: path to your current directory
$RCAC_SCRATCH: path to scratch filesystem
$PATH: all directories searched for commands/applications
$HOSTNAME: name of the machine you are on
$SHELL: your current shell (bash, tcsh, csh, ksh)
$SSH_CLIENT: your local client's IP address
$TERM: type of terminal or terminal emulator being used
$OMP_NUM_THREADS: number of OpenMP threads

All environment variables begin with the dollar sign ($) and are all uppercase. They may be used on the command line or in any scripts in place of and in combination with hard-coded values:

$ ls $HOME
...

$ ls $RCAC_SCRATCH/myproject
...

$ ls $RCAC_SCRATCH/myproject/$HOSTNAME_data
...

You may find the value of any environment variable by using the echo command:

$ echo $RCAC_SCRATCH
/scratch/scratch95/m/myusername

$ echo $SHELL
/usr/local/bin/tcsh

You may list the values of all environment variables using the env command:

$ env
USER=myusername
HOME=/home/ba01/u101/myusername
RCAC_SCRATCH=/scratch/scratch95/m/myusername
SHELL=/usr/local/bin/tcsh
...

You may create or overwrite an environment variable using either export or setenv, depending on your shell:

  (for bash and sh)
$ export VARIABLE=value

  (for tcsh and csh)
% setenv VARIABLE value

Storage Quotas / Limits

Your disk usage is limited on RCAC systems. However, each filesystem (scratch, home directory, etc.) may have a different limit. If you exceed the soft limit or quota, you will see warnings whenever writing to the disk that you are over quota, but the write will still succeed. If you exceed the hard limit or limit, your write will fail until you either remove other files or your quota is increased. Generally, RCAC systems do not impose a soft limit—only a hard limit.

Checking Quota Usage

You may find out what your current quota is by using the quota command:

$ quota
Disk quotas for user myusername (uid 12345): 
     Filesystem  blocks   quota   limit   grace   files   quota   limit   grace
     ba01:/u103 2346272       0 5000000           17508       0   65535

The columns are as follows:

Filesystem: This indicates the line is for the user's files on /u103/, which doing echo $HOME confirms is the user's home directory filesystem.
Blocks: This shows how many 1 KB blocks the user's files take up. In this case, 2346272 KB / 1024 = 2291 MB, or 2291 MB / 1024 = 2.24 GB.
Quota: This shows that soft limits are not being imposed (0).
Limit: This shows how many 1 KB blocks the user's hard limit is. In this case, (5000000 KB / 1024) / 1024 = 4.77 GB.
Grace: This would show the grace period (in days) for any soft limit (none in this case).
Files: This shows how many file pointers (inodes) the user is currently using. This is based more on the number of files and directories and not the size.
Quota: This shows that soft limits are not being imposed for file pointers (0).
Limit: This shows the user's file pointer hard limit. It is possible, though unlikely, to hit this and not the size limit if you create a large number of very small files.
Grace: This would show the grace period (in days) for any file pointer soft limit (none in this case).

You may also see the disk usage of any given directory by using du:

$ du -hs
1.1G    .

$ du -hs $HOME
138M    /home/ba01/u103/myusername

This can be very helpful in figuring out where your largest files or directories are, so that you may clean out unneeded large files and avoid hitting your quota.

Requesting Quota Increase

If you find you need additional disk space on an RCAC account, please first consider archiving and compressing old files and moving them to long-term storage. If this option does not resolve the issue, you may send an email to rcac-help@purdue.edu and request additional space.

Archive and Compression

There are several options for archiving and compressing groups of files or directories on RCAC systems. All of the following tools are provided:

zip (more information)
Simple compression and file packaging utility.
Examples:

  (compress file somefile.c)
$ zip somefile.zip somefile.c

  (extract contents of somefile.zip)
$ unzip somefile.zip

  (compress all files in a directory into one archive file)
$ zip -r somefile.zip somedirectory/

  (compress all ".c" files in current directory into one archive file)
$ zip -r somefile.zip . -i \*.c

tar (more information)
Saves many files together into a single archive file, and restores individual files from the archive. Includes automatic archive compression/decompression options and special features that allow tar to be used for incremental and full backups.
Examples:

  (archive file somefile.c)
$ tar cvf somefile.tar somefile.c

  (archive and compress file somefile.c)
$ tar czvf somefile.tar.gz somefile.c

  (list contents of archive somefile.tar)
$ tar tvf somefile.tar

  (extract contents of somefile.tar)
$ tar xvf somefile.tar

  (extract contents of gzipped archive somefile.tar.gz)
$ tar xzvf somefile.tar.gz

  (archive and compress all files in a directory into one archive file)
$ tar czvf somefile.tar.gz somedirectory/

  (archive and compress all ".c" files in current directory into one archive file)
$ tar czvf somefile.tar.gz *.c

gzip (more information)
Compression utility designed as a replacement for compress, with much better compression and no patented algorithms. The standard compression system for all GNU software.
Examples:
```
  (compress file somefile - also removes uncompressed file)
$ gzip somefile

  (uncompress file somefile.gz - also removes compressed file)
$ gunzip somefile.gz
```

bzip2 (more information)
Strong, lossless data compressor based on the Burrows-Wheeler transform. Also available as a library.
Examples:

  (compress file somefile - also removes uncompressed file)
$ bzip2 somefile

  (uncompress file somefile.bz2 - also removes compressed file)
$ bunzip2 somefile.bz2

compress (more information)
Adaptive Lempel-Ziv compressor. Not often used today.

Windows users can work with these same formats using some of the following software:

7-Zip
Free Windows software package that can handle all the above formats.
WinZip
Commercial Windows software package that can handle all the above formats.
WinRAR
Commercial Windows software package that can handle all the above formats.

File Transfer

There are a variety of ways to transfer data to and from RCAC systems. Which you should use depends on several factors, including the ease of use for you personally, connection speed and bandwidth, the size and number of files to be transferred.

FTP

FTP (File Transfer Protocol) is simple data transfer mechanism. FTP was not designed to provide secure communications, and so FTP is no longer supported on any RCAC systems. Most modern FTP clients support either SFTP or SCP however, which are similar, secure protocols for file transfer. Try using one of the other methods described here instead of FTP.

SCP

SCP (Secure CoPy) is a simple way of transferring files between two machines that use the SSH (Secure SHell) protocol. You may use SCP to connect to any system where you have SSH (log-in) access. SCP is available as a protocol choice in some graphical file transfer programs and also as a command line program on most Linux, Unix, and Mac OS X systems. SCP can copy single files, but will also recursively copy directory contents if given a directory name.

Command-line usage:

  (to a remote system from local)
$ scp sourcefilename myusername@hostname:somedirectory/destinationfilename

  (from a remote system to local)
$ scp myusername@hostname:somedirectory/sourcefilename destinationfilename

  (recursive directory copy to a remote system from local)
$ scp sourcedirectory/ myusername@hostname:somedirectory/

Linux / Solaris / AIX / HP-UX / Unix:

The "scp" command line program should already be installed.

Microsoft Windows:

WinSCP is a full-featured and free graphical SCP and SFTP client.
PuTTY also offers "pscp.exe", which is an extremely small program and a basic SCP client.
Secure FX is a commercial SCP and SFTP client which is available free to Purdue students, faculty, and staff with a Purdue career account.

Mac OS X:

The "scp" command line program should already be installed. You may start a local terminal window from "Applications->Utilities".

SFTP

SFTP (Secure File Transfer Protocol) is a reliable way of transferring files between two machines. You may use SFTP to connect to most RCAC systems. SFTP is available as a protocol choice in some graphical file transfer programs and also as a command-line program on most Linux, Unix, and Mac OS X systems. SFTP has more features than SCP and allows for other operations on remote files, remote directory listing, and resuming interrupted transfers. Command-line SFTP cannot recursively copy directory contents; to do so, try using SCP or graphical SFTP client.

Command-line usage:

$ sftp -B buffersize myusername@hostname

      (to a remote system from local)
sftp> put sourcefile somedir/destinationfile
sftp> put -P sourcefile somedir/

      (from a remote system to local)
sftp> get sourcefile somedir/destinationfile
sftp> get -P sourcefile somedir/

sftp> exit

-B: optional, specify buffer size for transfer; larger may increase speed, but costs memory
-P: optional, preserve file attributes and permissions

Linux / Solaris / AIX / HP-UX / Unix:

The "sftp" command line program should already be installed.

Microsoft Windows:

WinSCP is a full-featured and free graphical SFTP and SCP client.
PuTTY also offers "psftp.exe", which is an extremely small program and a basic SFTP client.
Secure FX is a commercial SFTP and SCP client which is available free to Purdue students, faculty, and staff with a Purdue career account.

Mac OS X:

The "sftp" command-line program should already be installed. You may start a local terminal window from "Applications->Utilities".
MacSFTP

LFTP

LFTP is a command-line file-transfer program for Linux and Unix systems. It supports SFTP, HTTP, and HTTPS file-transfers. LFTP has additional features not provided by SFTP such as bandwidth throttling, transfer queues, and parallel transfers. It may be used interactively or scripted.

LFTP with parallel transfers can be much faster than SCP or SFTP, so its use is encouraged when possible.

LFTP is provided only on some RCAC systems. However, it is simply a client, so it is not needed on the remote machine involved in a transfer (the remote system need only support SFTP).

Interactive usage:

$ lftp myusername@hostname

         (transfer all ".dat" files from remote system to local)
lftp :~> mget *.dat

         (transfer "filename.dat" file from local system to remote)
lftp :~> put filename.dat

         (transfer a directory and all contents from remote
          system to local, using 5 connections in parallel)
lftp :~> mirror --parallel=5 remotedirectory localdirectory/

         (transfer a directory and all contents from local
          system to remote, using 8 connections in parallel)
lftp :~> mirror -R --parallel=8 localdirectory remotedirectory/

Batch usage:

  (specify all actions on command line)
$ lftp myusername@hostname -e "mget *.dat"

  (specify all actions in the script file "mytransfer.lftp")
$ lftp myusername@hostname -f mytransfer.lftp

GridFTP

GridFTP is a fast method of transferring large files that uses Globus authentication credentials (x509 certificates). GridFTP is available on some RCAC resources, but only to users who are members of a Grid project, such as TeraGrid, NorthWest Indiana Computational Grid (NWICG), or Open Science Grid (OSG). Note that not all grids may access all RCAC resources.

For more information about how to use GridFTP, consult documentation for your participating grid.

Provided Applications

The third-party software on three commonly used RCAC systems is shown in the following table. Additional software may be available on other RCAC systems, and the software on a specific system can be seen by running the command "module avail" on that system. Please contact rcac-help@purdue.edu if you are interested in the availability of software not shown in this list.

	Radon	Steele	Julius/Caesar
R	✓	✓
AcGrace		✓
Amber	✓	✓
ANSYS	✓	✓
ATLAS	✓
BinUtils		✓
Boost	✓
ClustalX	✓
COMSOL	✓	✓	✓
CPLEX	✓	✓	✓
CUDA		✓
DX		✓
Ferret		✓
FFTW	✓	✓
FLUENT	✓	✓
GAMESS	✓	✓
GAMS	✓	✓
Gaussian	✓	✓	✓
GCC Compiler (C, C++, Fortran)	✓	✓	✓
GCC IA64 Cross-Compiler (xgcc-ia64)		✓
GMP	✓
GMT	✓	✓
GrADS		✓
GROMACS		✓
GhostScript		✓
GSL		✓	✓
HDF4 (Compiled for Intel, GNU, PGI)		✓
HDF5 (Compiled for Intel, GNU, PGI)		✓
ImageMagick		✓
IMSL	✓	✓	✓
Intel Compiler (C, C++, Fortran)	✓	✓	✓
Jasper	✓	✓
Java	✓	✓
LAM			✓
LAMMPS	✓	✓
LSTC			✓
Maple	✓	✓	✓
Mathematica	✓	✓	✓
MATLAB	✓	✓
Mitrionics FPGA Tools (mitrion)		✓
MPFR	✓	✓	✓
MPICH	✓	✓	✓
MPICH2		✓	✓
MPIExec		✓
MrBayes	✓
MUMPS		✓
MVAPICH (for Intel, PGI compilers)		✓
MVAPICH2 (for Intel, GNU, PGI compilers)		✓
MWRank	✓
NCBI	✓
NCL	✓	✓
NCO		✓
NetCDF (for Intel, GNU, PGI compilers)		✓
NTL	✓
NWChem	✓	✓
Octave		✓
PGI Compiler (C, C++, Fortran)	✓	✓
PKG-Config		✓
Python	✓	✓
RASC		✓	✓
SAS	✓
ScaLAPACK	✓	✓	✓
Stata			✓
Subversion	✓	✓	✓
Tau		✓
TecPlot		✓
TotalView	✓	✓	✓
UDUNITS		✓
VASP			✓
Vis5D		✓

Environment Management with the Module Command

RCAC uses the module command as the preferred method for a user to manage the processing environment. With this command, a user may load libraries and paths for using specific applications or compilers. These are organized into packages which may be loaded and unloaded as needed. Please use the module command and do not manually configure your environment, as RCAC staff will frequently make changes to the specifics of various packages. If you use the module command to manage your environment, these changes will not be noticeable.

Below follows a short introduction to the module command. You can see more in the man page for module. Typing module at the command line will give you a brief usage report.

List Available Modules

To see what modules are available on this system, use the "module avail" command:

$ module avail

------------------------ /apps/host/modules/versions -------------------------
3.1.6

-------------------- /apps/host/modules3.1.6/modulefiles ---------------------
dot         module-cvs  module-info modules     null        use.own

----------------------- /apps/host/modules/modulefiles -----------------------
R/2.6.2
R/2.7.0
amber/10
ansys/11.0
dx/4.4.4
fftw/2.1.5
fftw/3.1.2
fluent/6.3.26
gamess/24.MAR.2007.R3(default)
gaussian/D.01
gaussian/E.01(default)
gaussian03/D.01
gaussian03/E.01(default)
gcc/4.3.0
     ...

Load / Unload a Module

You should note that all modules consist of both a name and a version number. When loading a module, you may use only the name to load the default version, or specify which version you wish to load:

$ module load intel
  (load default Intel compiler)

$ module load intel/9.1.045
  (load version 9.1.045 of the Intel compiler)

Note that you will need to load any relevant modules within job submission scripts that use those applications. Loading the module before submitting your job is not sufficient. Also, if you use bash or ksh as your login shell, you will also need to add a line in any submission script to source /etc/profile before invoking "module". Users of csh and tcsh do not need to do this.

     ...
. /etc/profile
module load intel
     ...

To unload a module, use the “module unload” command. It will attempt to undo the changes to your environment, made by that module:

$ module unload intel
  (unload default Intel compiler)

$ module unload intel/9.1.045
  (unload version 9.1.045 of the Intel compiler)

List Currently Loaded Modules

To see what modules you have currently loaded, use "module list":

$ module list
Currently Loaded Modulefiles:
  1) intel/9.1.045

$ module unload intel
$ module list
No Modulefiles Currently Loaded.

Show Module Details

To learn more about what a module does to your environment, you may use the "module show module_name" command, where module_name is any name in the list from command "module avail". This can be either default name like "intel", "gcc", "pgi", and "matlab", or a specific version of amodule, such as "intel/9.1.045". Here is an example showing what loading the default Intel compiler does to the processing environment:

$ module show intel
-------------------------------------------------------------------
/opt/modules/modulefiles/intel/9.1.045:

module-whatis    invoke Intel 9.1 Compilers 
prepend-path     PATH /opt/intel/cce/9.1.045/bin 
prepend-path     PATH /opt/intel/fce/9.1.040/bin 
prepend-path     PATH /opt/intel/idbe/9.1.045/bin 
prepend-path     LD_LIBRARY_PATH /opt/intel/cce/9.1.045/lib 
prepend-path     LD_LIBRARY_PATH /opt/intel/fce/9.1.040/lib 
prepend-path     LD_LIBRARY_PATH /opt/intel/idbe/9.1.045/lib 
prepend-path     LD_LIBRARY_PATH /opt/intel/mkl/9.0/lib/em64t 
setenv           CC icc 
setenv           CXX icpc 
setenv           FC ifort 
setenv           F90 ifort 
setenv           LAPACK_INCLUDE -I/opt/intel/mkl/9.0/include 
setenv           LINK_LAPACK -L/opt/intel/mkl/9.0/lib/em64t \
-lmkl_lapack64 -lmkl_em64t -lmkl -lguide -lpthread 
setenv           LINK_LAPACK_STATIC -L/opt/intel/mkl/9.0/lib/em64t \ 
-lmkl_lapack -lmkl_em64t -lguide -lpthread 
-------------------------------------------------------------------

To show what loading a specific Intel compiler version does to the processing environment.

$ module show intel/9.1.045
-------------------------------------------------------------------
/apps/steele/modules/modulefiles/intel/9.1.045:

module-whatis    invoke Intel 9.1 Compilers 
prepend-path     PATH /opt/intel/cce/9.1.045/bin 
prepend-path     PATH /opt/intel/fce/9.1.040/bin 
prepend-path     PATH /opt/intel/idbe/9.1.045/bin 
prepend-path     LD_LIBRARY_PATH /opt/intel/cce/9.1.045/lib 
prepend-path     LD_LIBRARY_PATH /opt/intel/fce/9.1.040/lib 
prepend-path     LD_LIBRARY_PATH /opt/intel/idbe/9.1.045/lib 
prepend-path     LD_LIBRARY_PATH /opt/intel/mkl/9.1/lib/em64t 
setenv           CC icc 
setenv           CXX icpc 
setenv           FC ifort 
setenv           F90 ifort 
setenv           ICC_HOME /opt/intel/cce/9.1.045 
setenv           IFORT_HOME /opt/intel/fce/9.1.040 
setenv           MKL_HOME /opt/intel/mkl/9.1 
setenv           LAPACK_INCLUDE -I/opt/intel/mkl/9.1/include 
setenv           LINK_LAPACK -L/opt/intel/mkl/9.1/lib/em64t -lmkl_lapack -lmkl_em64t -lmkl -lguide -lpthread 
setenv           LINK_LAPACK_STATIC -L/opt/intel/mkl/9.1/lib/em64t -lmkl_lapack -lmkl_em64t -lguide -lpthread 
-------------------------------------------------------------------

Provided Compilers

Compilers are available on Gold for Fortran 77, Fortran 90, Fortran 95, C, and C++. The compilers can produce general-purpose and architecture-specific optimizations to improve performance. These include loop-level optimizations, inter-procedural analysis and cache optimizations. The compilers support automatic and user-directed parallelization of Fortran, C, and C++ applications for multiprocessing execution. More detailed documentation on each compiler set available on Gold follows.

IBM Compiler Set

To use the IBM compiler set on Gold, you need load no modules. The compiler programs will already be in your path. Here are some examples:

Language	Serial Program	MPI Program	OpenMP Program
Fortran77	$ xlf_r myprogram.f -o myprogram	$ mpxlf myprogram.f -o myprogram	$ xlf_r -qsmp=omp myprogram.f -o myprogram
Fortran90	$ xlf90_r myprogram.f -o myprogram	$ mpxlf90 myprogram.f -o myprogram	$ xlf90_r -qsmp=omp myprogram.f -o myprogram
Fortran95	$ xlf95_r myprogram.f -o myprogram	$ mpxlf95 myprogram.f -o myprogram	$ xlf95_r -qsmp=omp myprogram.f -o myprogram
C	$ xlc_r myprogram.c -o myprogram	$ mpcc myprogram.c -o myprogram	$ xlc_r -qsmp=omp myprogram.c -o myprogram
C++	$ xlC_r myprogram.cpp -o myprogram	$ mpCC myprogram.cpp -o myprogram	$ xlC_r -qsmp=omp myprogram.cpp -o myprogram

More information on compiler options can be found in the official man pages, which can be accessed using the "man" command, or online here:

Here is some more documentation from other sources on the IBM compilers:

Compiling OpenMP Programs

Compilers for C, C++, and versions of Fortran are available. To see a Fortran 77 program with OpenMP commands: omp_hello_f77.f. To see a C program with OpenMP commands: omp_hello.c. See the table below for how to compile your program. Any compiler flags accepted by ifort/icc compilers, can be used with OpenMP.

Language	Command example, Intel	Command example, GNU	Command example, PGI
C	icc -openmp program.c -o program	gcc -fopenmp program.c -o program	pgcc -mp program.c -o program
C++	icc -openmp program.cpp -o program	g++ -fopenmp program.cpp -o program	pgCC -mp program.cpp -o program
Fortran 77	ifort -openmp program.f -o program	-	pgf77 -mp
Fortran 90	ifort -openmp program.f90 -o program	gfortran -fopenmp program.f90 -o program	pgf90 -mp program.f90 -o program
Fortran 95	ifort -openmp program.f90 -o program	gfortran -fopenmp program.f90 -o program	pgf95 -mp program.f90 -o program

Compiling a Fortran 90 program gives the following output when successful (note that the compiler module is loaded first - in this example Intel):

	$ module load intel
	$ ifort -openmp omp_hello_90.f90 -o omp_hello
	omp_hello_90.f90(4): (col. 9) remark: OpenMP DEFINED REGION WAS PARALLELIZED.

A compilation of the example C program gives the following output when successful (also Intel):

	$ icc -openmp omp_hello.c -o omp_hello
	omp_hello.c(15): (col. 1) remark: OpenMP DEFINED REGION WAS PARALLELIZED.
	$

Note that in general, neither GNU nor PGI compilers will output anything for a successful compilation.

Compiling MPI Programs

Compilers for C, C++, and versions of Fortran are available. To see a Fortran 77 program with MPI commands: hello77.f. To see a C program with MPI commands: hello.c. See the table below for how to compile your program. Any compiler flags accepted by ifort/icc compilers, can be used with mpif77/mpicc.

Language	Command Example (Intel, GNU, PGI)
C	mpicc program.c -o program
C++	mpiCC program.C -o program
Fortran 77	mpif77 program.f -o program
Fortran 90	mpif90 program.f -o program

Compiling a Fortran 90 MPI program gives no output when successful:

	$ module load mpich2-intel
	$ mpif90 hello.f90 -o hello
	$

A compilation of a C MPI program gives no output when successful:

	$ mpicc hello.c -o hello
	$

Note that in general, neither Intel, GNU, or PGI compilers will output anything for a successful compilation.

Compiling Hybrid Programs

Compilers for C, C++, and versions of Fortran are available. To see a hybrid C++ program with OpenMP/MPI commands: hybrid.cpp. See the table below for how to compile your hybrid (OpenMP/MPI) program. Any compiler flags accepted by ifort/icc compilers, can be used with OpenMP.

Language	Command example, Intel	Command example, GNU	Command example, PGI
C	mpicc -openmp program.c -o program	mpicc -fopenmp program.c -o program	mpicc -mp program.c -o program
C++	mpiCC -openmp program.C -o program	mpiCC -fopenmp program.C -o program	mpiCC -mp program.C -o program
Fortran 77	mpif77 -openmp program.f -o program	-	mpif77 -mp program.f -o program
Fortran 90	mpif90 -openmp program.f -o program	mpif90 -fopenmp program.f -o program	mpif90 -mp program.f -o program

Example: (Compiling the C++ program mentioned above)

	$ module load mpich2-intel
	$ mpiCC -openmp hybrid.cpp -o hybrid
	hybrid.cpp(73): (col. 30) remark: OpenMP DEFINED LOOP WAS PARALLELIZED.
	hybrid.cpp(73): (col. 30) remark: OpenMP DEFINED REGION WAS PARALLELIZED.
	hybrid.cpp(34): (col. 3) remark: OpenMP DEFINED LOOP WAS PARALLELIZED.
	hybrid.cpp(25): (col. 1) remark: OpenMP DEFINED REGION WAS PARALLELIZED.
	$

Provided Libraries

A number of libraries are installed on Gold. They include:

BLAS levels 1, 2, 3
BLACS 1.1
ESSL
PESSL
MASSL

IBM's "built-in" math libraries are invoked at compile time, and you will thus see (with the env command for example) that the expected LD_LIBRARY_PATH variable is missing.

The MASS group: this is actually three threadsafe libraries, which may be used to speed up intrinsics like cos, sqrt, tan, etc. They may be called from either FORTRAN or C (but C only supports calls by reference).

The three most interesting libraries are: libmass.a (-lmass) - supporting scalar calls, libmassv.a (-lmassv) - supporting vector calls, and [libmassvp3.a (-lmassvp3), libmassvp4.a (-lmassvp4), libmassvp5.a (-lmassvp5), and libmassvp6.a (-lmassvp6) - supporting vector calls tuned specifically for the Power3 and higher architectures.

The ESSL (Engineering and Scientific Subroutine Libraries) group: this contains subsets of the BLAS and LAPACK libraries among many others. Two thread-safe libraries in this group are of particular interest. If you plan to calculate a function on a single processor, the libessl.a (-lessl) should be used. If you wish to take advantage of multiple threads to calculate the function, the libesslsmp.a (-lesslsmp) library should be used, and the environment variable, XLSMPOPTS, should be set to declare the number of threads to be created for the calculation.

If you are using a generic BLAS (levels 1, 2, or 3), the call is straightforward, but ESSL does not support modified plane rotations. If you are used to calling a LAPACK driver routine, most of these calls do not exist. For example, a call to SGESV does not exist. However, the functionality of this call does exist.

From the site http://www.netlib.org/ a search on SGESV will bring you to http://www.netlib.org/lapack/single/sgesv.f, which is the source code for theSGESV driver. This driver is actually only a simple subroutine containing an "if" statement (for error checking) and two calls to LAPACK computational subroutines, SGETRF and SGETRS. Both of these subroutines exist in the ESSL libraries and use the same inputs as the original SGESV call. Thus, SGESV can be successfully implemented in your code through ESSL. Other drivers may be invoked using the same procedure.

There is some information about ESSL and linking with it, on IBM's site: http://publib.boulder.ibm.com/infocenter/clresctr/vxrx/index.jsp?topic=/com.ibm.cluster.essl.doc/esslbooks.html.

The PESSL libraries: Those users who have codes which utilize PBLAS, BLACS, or ScaLAPACK subroutines, can find these subroutines in the thread-safe PESSL libraries. They are structured much the same as the ESSL libraries with both a serial (-lpessl) and a multi-threaded (-pesslsmp) library for use. Once again, driver routines may not exist, but the actual computational subroutines may be accessed through the libraries.

PESSL is accessed like this: xlf myprog.f -lpessl.

More information can be found here: http://people.scs.fsu.edu/~burkardt/f_src/pessl/pessl.html

MPICH Library

MPICH2 (and MPICH) is available for some compiler combinations on Gold. Refer to the compilers section for an overview of how to link in MPICH2 support. Here are some more documentation from other sources on the MPICH2 and MPICH libraries:

Intel Math Kernel Library (MKL)

Intel Math Kernel Library (MKL) contains ScaLAPACK, LAPACK, Sparse Solver, BLAS, Sparse BLAS, CBLAS, GMP, FFTs, DFTs, VSL, VML, and Interval Arithmetic routines. MKL can be found in the directory "/opt/intel/mkl/9.1" and it is divided into the following subdirectory structure:

lib/32 – Libraries for 32-bit Applications
- libmkl_ia32.a – Optimized Kernels (BLAS, CBLAS, Sparse BLAS, GMP, FFTs, DFTs, VML, VSL, Interval Arithmetic)
- libmkl_lapack.a – LAPACK Routines
- libmkl_lapack95.a – LAPACK95 Interface (libmkl_lapack.a also required)
- libmkl_solver.a – Sparse Solver Routines
- libguide.a – Threading Library for Static Linking
lib/em64t – Libraries for Intel EM64T Applications
- libmkl_em64t.a – Optimized Kernels (BLAS, CBLAS, Sparse BLAS, GMP, FFTs, DFTs, VML, VSL, Interval Arithmetic)
- libmkl_lapack.a – LAPACK Routines
- libmkl_lapack95.a – LAPACK95 Interface (libmkl_lapack.a also required)
- libmkl_solver.a – Sparse Solver Routines
- libguide.a – Threading Library for Static Linking
lib/64 – Libraries for Itanium 2 Applications
- libmkl_ipf.a – Optimized Kernels (BLAS, CBLAS, Sparse BLAS, GMP, FFTs, DFTs, VML, VSL, Interval Arithmetic)
- libmkl_lapack.a – LAPACK Routines
- libmkl_lapack95.a – LAPACK95 Interface (libmkl_lapack.a also required)
- libmkl_solver.a – Sparse Solver Routines
- libguide.a – Threading Library for Static Linking

Here are some example combinations of linking options:

  (static linking of LAPACK and Kernels)
$ <fortran_compiler> myprogram.f -L${MKLPATH} -lmkl_lapack -lmkl_ia32 -lguide -lpthread

  (static linking of Fortran-95 LAPACK Interface and Kernels)
$ <fortran_compiler> myprogram.f95 -L${MKLPATH} -lmkl_lapack95 -lmkl_lapack -lmkl_ia32 -lguide -lpthread

  (static linking of BLAS, Sparse BLAS, GMP, VML/VSL, Interval Arithmetic, and FFT/DFT)
$ <c_compiler> myprogram.c -L${MKLPATH} -lmkl_ia32 -lguide -lpthread -lm

  (dynamic linking of BLAS or FFTs)
$ <c_compiler> myprogram.c -L${MKLPATH} -lmkl -lguide -lpthread

It is recommended that you use dynamic linking of libguide. If so, ensure LD_LIBRARY_PATH is defined such that the correct version of libguide is found and used at run time. If you use static linking of libguide (discouraged), then:

If you use the Intel compilers, link in the libguide version that comes with the compiler (use the -openmp option).
If you do not use the Intel compilers, link in the libguide version that comes with the Intel MKL above.

Here are some more documentation from other sources on the Intel MKL:

Using cpp with Fortran

If the source file ends with .F, .fpp, or .FPP, it is automatically preprocessed by cpp before it is compiled. If you want to use the C preprocessor with source files that do not end with .F, use the following compiler option to specify the filename suffix:

GNU: -x f77-cpp-input

  Note that the preprocessing is not extended to the contents of 
  files included by the "INCLUDE" directive - the #include 
  preprocessor directive must be used instead.

For example, to preprocess source files that end with .f:

    gfortran -x f77-cpp-input program.f

Intel: -cpp

  To tell the compiler to link using C++ runtime libraries 
  included with gcc/icc, use -cxxlib -gcc/-cxxlib -icc.

For example, to preprocess source files that end with .f:

    ifort -cpp program.f

Generally, it is best to rename the file from <name>.f to <name>.F. The preprocessor will then be run automatically when the file is compiled.

A good page to look at for combining C/C++ and Fortran, is Using C/C++ and Fortran together.

Calling Fortran from C/C++

When calling your own Fortran routines from C/C++, you should not append an underscore (_) after the name.

A complete list of routines is in the XL Fortran Language Reference Manual.

Here are some links to pages that discuss how to use Fortran from C/C++:

Running Jobs on Gold

There are a number of different compilers and programs installed on the RCAC systems. To access them, use module load <program>. To see the available modules, type module avail. To read more about the "module" command, look here.

There are two methods for submitting jobs to the Gold community cluster. First, you may submit jobs directly to a queue on Gold. These jobs may be serial, message-passing, or shared-memory in nature. You use the Portable Batch System (PBS) to submit jobs to a queue. Secondly, the Gold cluster is a part of BoilerGrid. You may submit serial jobs to BoilerGrid and specifically request that the serial jobs be run on the resources on Gold.

Running Jobs via PBS

Gold uses PBS version 9.x. The newer versions have a few minor differences from the older versions (before 8.0).

Differences are mainly:

Use of "cpp" no longer supported
Hosts in $PBS_NODEFILE ordered differently

The Portable Batch System (PBS) is a richly featured workload management system providing job scheduling and job management interface on computing resources, including Linux clusters. With PBS, a user requests resources and submits a job to a queue. A description of Gold's queues follows further down.

Note that you should never run big, long, multi-threaded, or CPU-intensive jobs on the front-end host. The front-end hosts are community-owned and running anything but the smallest test-job will slow them down for everyone. Use PBS to submit the job as a job submission file (called a job script in the official manual) or run an interactive PBS job session.

Gold PBS Tips

PBS Queues. Always use qstat -Q to determine which queues are available. There will usually be queues which are available to everyone with an account on that system. On most systems these are called either "standby" or "workq".
Any program that is installed can be run interactively. You must still use the "module load <program>" command to access it.
Programs which open a display can also be run interactively. Just use the -v DISPLAY option to qsub.
You can see which nodes you are using on one of the cluster machines with the command: cat $PBS_NODEFILE
When running OpenMP programs, you need the processors to be on the same node to get the advantage of shared memory.
The order of the processors is random. There is no way to tell which processor will do what and in which order in a parallel program.
Remember that ncpus can not be larger than the number of processors on each node on the machine in question.

Gold PBS Queues

Gold has only one queue, and it is open for everyone with an account on the machine.

Name of queue	Type	Nodect (Max/default)	Default Walltime	Max Walltime	Notes
workq	Execution	1/4	00:30:00	144:00:00	The 'open' queue which can be used by all users. Access to all processors

Gold PBS Submission Script

A job submission file (job script) can contain any of the commands that you would otherwise issue yourself from the command line. You can, for example both compile and run a program and also set any necessary environment values. The results from compiling or runnning your programs can usually be seen after the job has run. They will show up in your directory as the files <script_name>.e<job number> and <script_name>.o<job number>. The first file will contain any errors that were reported (hopefully none), and the second file will give any results that your program may have output to the screen. If the program is supposed to write the results to a file, this will of course still happen. The job number is a number which PBS gives to every job. This will be reported when the job is submitted.

It may take quite a while before the job finishes running. How long will, among other things, depend on the number of nodes you have requested, how large the program is, which queue you are running it in, and how many other people are using the system at the same time.

A job submission file may consist of PBS directives, comments and executable statements. A PBS directive provides a way of specifying job attributes in addition to the command line options. For example:

	#PBS -N Job_name
	#PBS -l select=4:mem=320kb,walltime=10:30
	#PBS -m be
	#
	step1 arg1 arg2
	step2 arg3 arg4

The -N Job-name replaces script_name of the error and output files. The qsub command scans the lines of the script file for directives. An initial line in the script that begins with the characters "#!" or the character ":" will be ignored and scanning will start with the next line. Scanning will continue until the first executable line, that is a line that is not blank, not a directive line, nor a line whose first non-white space character is "#". If directives occur on subsequent lines, they will be ignored.

The remainder of the directive line consists of the options to qsub in the same syntax as they appear on the command line. The option character is to be preceded with the "-" character.

If an option is present in both a directive and on the command line, that option and its argument, if any, will be ignored in the directive. The command line takes precedence.

If an option is present in a directive and not on the command line, that option and its argument, if any, will be processed as if it had occurred on the command line.

How you run a program depends on whether it is a serial program, an OpenMP program, or a MPI program. There is no difference in how to run the program for the various compilers.

Important: You must 'module load' the same compiler (and MPICH2 if needed) that you used for compiling. Note that it is not necessary to load the standard compiler if you have loaded the corresponding compiler with the MPICH2 libraries included.

PBS Job Submission

The command to submit the job submission file is the following:

	qsub -q standby -l select=4,walltime=1:00 run_hello

This example submits a job to queue 'standby' and requests 4 nodes. It has a walltime of 1 minute. The job submission file is called run_hello. The names of the queues will be different on the various RCAC systems. You can find a list of their names with the command qstat -q or look at the section 'Queues'.

Some useful options for the qsub command includes (in the list below, note that a chunk is defined as a set of resources that are to be allocated as a unit):

-q <name>: tells which queue you want the job to run in. A list of available queues can be seen using the command qstat -Q. If none is choosen, the batch server will be the default server.
-l select=[N:]chunk[+[N:]chunk ...], where N specifies how many of that chunk, and a chunk is of the form: resource_name=value[:resource_name=value ...]

Job-wide resource_name=value requests are of the form: -l resource_name=value[,resource_name=value ...]. The most important resource_name's are: node (required), ncpus (how many processors), mpiprocs (how many processes).
The place statement has this form: -l place=[ arrangement ][: sharing ][: grouping] where
- arrangement is one of free | pack | scatter
- sharing is one of excl | shared
- grouping can have only one instance of group=resource
and where
- free: Place job on any node(s). Only good if you have a job that does not need much memory, so you do not mind it sharing the node with other. Will most likely give you access quicker than the other options.
- pack: You will get processors on one node only - all jobs will be placed on one node. Good for OpenMP.
- scatter: The chunks with any MPI processes will be spread out across as many of the nodes as possible, attempting to put only one process on each. A chunk with no MPI processes may be taken from the same node as another chunk.
- excl: Only this job uses the nodes chosen.
- shared: This job can share the nodes chosen.
- group=resource: Chunks will be grouped according to a resource. All nodes in the group must have a common value for the resource, which can be either the built-in resource host or a site-defined node-level resource.
Note that nodes can have sharing attributes that override job placement requests.
-I: Job is to be run interactively.
-v variable_list: Expands the list of environment variables that are exported to the job. This can also be environment variables from the qsub command environment which are made available to the job when it executes. The variable_list is a comma separated list of strings of the form variable or variable=value. These variables and their values are passed to the job.
-V: Declares that all environment variables in the qsub command's environment are to be exported to the batch job.

Note that ncpus can not be larger than the number of processors on each node on the machine in question.

Some environment variables can be set. They are then available to PBS. They include:

PBS_O_HOST: the name of the host upon which the qsub command is running
PBS_O_QUEUE: the name of the original queue to which the job was submitted
PBS_O_SYSTEM: the operating system name given by uname -s on the host on which qsub is running
PBS_O_WORKDIR: the absolute path of the current working directory of the qsub command
PBS_ENVIRONMENT: set to PBS_BATCH to indicate the job is a batch job, or to PBS_INTERACTIVE to indicate the job is a PBS interactive job, see -I option
PBS_JOBID: the job identifier assigned to the job by the batch system
PBS_JOBNAME: the job name supplied by the user
PBS_NODEFILE: the name of the file containing the list of nodes assigned to the job
PBS_QUEUE: the name of the queue from which the job is executed

If you wish to interrupt qsub prior to job start (before you get a command-line prompt), this can be done by typing control-C. It will then query if the user wishes to exit. If the user responds "yes", qsub exits and that job is aborted.

Instead of using a job submission file, qsub also accepts commands from standard input - the keyboard. To use this option, avoid giving a script operand or give the single character "-". When the script is being read from Standard Input, qsub will copy the file to a temporary file. This temporary file is passed to the library interface routine pbs_submit. The temporary file is removed by qsub after pbs_submit returns or upon the receipt of a signal which would cause qsub to terminate.

Once the job has started execution, input to and output from the job pass through qsub. Keyboard-generated interrupts are passed to the job. Entries beginning with the tilde ('~') character and containing special sequences are escaped by qsub. The recognized escape sequences are:

	~.      Qsub terminates execution. The batch job is 
                also terminated.
	
	~susp   Suspend the qsub program if running under the C shell. 
	        "susp" is the suspend character, usually CNTL-Z.
	
	~asusp  Suspend the input half of qsub (terminal to job), 
	        but allow output to continue to be displayed. Only 
                works under the C shell.  "asusp" is the auxiliary 
                suspend character, usually CNTL-Y.

If no script is provided, the qsub command reads the script from standard input. When the script is being read from Standard Input, qsub will copy the file to a temporary file. This temporary file is passed to the library interface routine pbs_submit. The temporary file is removed by qsub after pbs_submit returns or upon the receipt of a signal which would cause qsub to terminate.

Note: The following warning applies for users of the c-shell, csh. If the job is executed under the csh and a .logout file exists in the home directory in which the job executes, the exit status of the job is that of the .logout script, not the job submission file. This may impact any interjob dependencies. To preserve the job exit status, either remove the .logout file or place the following line as the first line in the .logout file:

	set EXITVAL = $status

and the following line as the last executable line in .logout

	exit $EXITVAL

PBS Job Status

Using the command qstat -a will show you the jobs currently running and their ID's.

Example (run on Steele):

$ qstat -a 

steele-adm.rcac.purdue.edu:
                                                            Req'd  Req'd   Elap
Job ID          Username Queue    Jobname    SessID NDS TSK Memory Time  S Time
--------------- -------- -------- ---------- ------ --- --- ------ ----- - -----
77025.steele-ad user123  standby  hello         --    1   8    --  00:05 Q   --
115505.steele-a user456  ncn      job4         5601   1   1    --  600:0 R 575:0
...
189479.steele-a user456  standby  AR4b          --    5  40    --  04:00 H   --
189481.steele-a user789  standby  STDIN        1415   1   1    --  00:30 R 00:07
189483.steele-a user789  standby  STDIN        1758   1   1    --  00:30 R 00:07
189484.steele-a user456  standby  AR4b          --    5  40    --  04:00 H   --
189485.steele-a user456  standby  AR4b          --    5  40    --  04:00 Q   --
189486.steele-a user123  tg_workq STDIN         --    1   1    --  12:00 Q   --
189490.steele-a user456  standby  job7        26655   1   8    --  04:00 R 00:06
189491.steele-a user123  standby  job11         --    1   8    --  04:00 Q   --
$

Where 'Q' = Queued, 'R' = Running, and 'H' = Held.

The list can be very long, making it difficult to find your own runs. If that is the case, use the following command to ask for jobs submitted by a specific user:

$ qstat -a -u user123

steele-adm.rcac.purdue.edu: 
                                                            Req'd  Req'd   Elap
Job ID          Username Queue    Jobname    SessID NDS TSK Memory Time  S Time
--------------- -------- -------- ---------- ------ --- --- ------ ----- - -----
182792.steele-a user123  standby job1   28422   1   4    --  23:00 R 20:19
185841.steele-a user123  standby job2   24445   1   4    --  23:00 R 20:19
185844.steele-a user123  standby job3   12999   1   4    --  23:00 R 20:18
185847.steele-a user123  standby job4   13151   1   4    --  23:00 R 20:18
$

PBS Job Cancellation

Stopping the job before it finishes.

qdel <job id>

You get the job id from the qstat -a or qstat -a -u [username] command.

PBS Interactive Jobs

To use the PBS queue interactively, you have to use the -I option. The command to submit such a job would then be like this command

	qsub -I -q standby -l select=2:ncpus=2

Where the options used means the following:

-q <name>: the queue you want the job to run in. A list of available queues can be seen using the command qstat -Q. If none are choosen, the batch server will be the default server.
-l select=[N:]chunk[+[N:]chunk ...], where N specifies how many of that chunk, and a chunk is of the form: resource_name=value[:resource_name=value ...]

Job-wide resource_name=value requests are of the form: -l resource_name=value[,resource_name=value ...]. An example of a resource_name is ncpus, which is number of CPU's.

The place statement has this form: -l place=[ arrangement ][: sharing ][: grouping]

where

- arrangement is one of free | pack | scatter
- sharing is one of excl | shared
- grouping can have only one instance of group=resource

and where

free: Place job on any node(s). Only good if you have a job that does not need much memory, so you do not mind it sharing the node with others. Will most likely give you access quicker than the other options.
pack: You will get processors on one node only - all jobs will be placed on one node. Good for OpenMP.
scatter: The chunks with any MPI processes will be spread out across as many of the nodes as possible, attempting to put only one process on each. A chunk with no MPI processes may be taken from the same node as another chunk.
excl: Only this job uses the nodes chosen.
shared: This job can share the nodes chosen.
group=resource: Chunks will be grouped according to a resource. All nodes in the group must have a common value for the resource, which can be either the built-in resource host or a site-defined node-level resource.

Note that nodes can have sharing attributes that override job placement requests.
-I: Job is to be run interactively.

As mentioned, the -I option must be specified for the job to be interactive. After opening an interactive session, we may run programs in the normal way. For running serial programs, you should only ask for one "chunk". Parallel programs can be run with the preferred number of nodes, which should be specified with -l select=<# nodes> when qsub is started.

Note that ncpus can not be larger than the number of processors on each node on the machine in question.

To open a display when running interactively, start the interactive session with the following command:

	qsub -I -q <queue> -l select=< (number of nodes)>:ncpus=< (number of processors)> -v DISPLAY

To end an interactive job, just type exit. If you wish to interrupt qsub prior to job start, this can be done by typing control-C. It will then query if the user wishes to exit. If the user responds "yes", qsub exits and the job is aborted.

To see which nodes your job is using:

	cat $PBS_NODEFILE

It is strongly suggested that you only use an interactive session for developmental tasks (such as debugging). Use a PBS job submission file when running the finished program.

PBS Examples

A large part of submitting a job involves understanding how to request computing resources. This section contains examples of submitting PBS jobs, both using a batch script and interactively. There will be separate examples for MPI and OpenMP jobs. Note that the sections 'batch' and 'interactive' have some examples which might also be relevant for, say, MPI and OpenMP.

PBS Batch Examples

This simple example submits the script 'run_hello' to the 'standby' queue on Steele and requests 4 nodes.

	-bash-3.00$ qsub -q standby -l select=4,walltime=1:00 run_hello
	99.steele-adm.rcac.purdue.edu
	-bash-3.00$

Doing a ls in your directory will now show two new files:

	-bash-3.00$ ls
	hello                            run_hello
	hello.c                          run_hello.e99
	hello.out                        run_hello.o99
	-bash-3.00$

If everything went well, then the file 'run_hello.e99' will be empty, since it contains any error messages your program gave while running. The file 'run_hello.o99' contains the output from your program.

Compiling through job submission files

If you want to do more than just run a program - say, you want to compile a MPI/C program, then you would need to first load the compiler you wish to use. This must be done in the job submission file. To load a compiler, you use module load <compiler>. To load a compiler with MPICH2 included, you use module load mpich2-<compiler>.

Here is an example of a job submission file which would work if you wanted to compile a MPI/C program with the Intel compiler:

Tcsh:

	module load mpich2-intel
	cd $PBS_O_WORKDIR
	mpicc program.c -o program

Bash:

	source /etc/profile
	module load mpich2-intel
	cd $PBS_O_WORKDIR
	mpicc program.c -o program

It is necessary to include the 'source /etc/profile' under bash/ksh, to be able to use the 'module load' command.

The command to submit a job is the following:

	qsub -q standby -l select=4,walltime=1:00 run_program

Where the options used means the following:

-q <name>: tells which queue you want the job to run in. A list of available queues can be seen using the command qstat -Q.
-l select: tells the job how many "chunks" (CPUs) you want to use (4 in the example) and
walltime=hh:mm:ss defines how much wall clock time it has (in the example it is set to 1 minute).

Submitting this script now gives the following result (it will take a while before the job is completed):

	-bash-3.00$ qsub -q standby -l select=4,walltime=1:00 run_hello
	106361.steele-adm.rcac.purdue.edu
	-bash-3.00$

Doing a 'ls' in your directory will now show two new files:

	bash-2.05a$ ls
	hello                            run_hello
	hello.c                          run_hello.e106361
	hello.out                        run_hello.o106361
	bash-2.05a$

If everything went well, then the file 'run_hello.e106361' will be empty, since it contains any error-messages your program gave while running. The file 'run_hello.o106361' contains the output from your program.

Getting the environment variables through a job submission file

If you would like to see the value of the environment variables, then you can make a job submission file like this - called env.job.

	# Ask for four nodes, 1 processor on each. 
	#PBS -l select=4:ncpus=1,walltime=00:01:30
	
	# Change to directory where job was submitted.
	cd $PBS_O_WORKDIR
	
	# Load for run-time the same module used for compilation:
	module load gcc
	
	# Show details, especially nodes.
	# PBS_NODEFILE contains a names of assigned nodes.
	# The results of most of the following commands appear in the error file.
	cat $PBS_O_HOST
	cat $PBS_O_QUEUE
	cat $PBS_O_SYSTEM
	cat $PBS_O_WORKDIR
	cat $PBS_ENVIRONMENT
	cat $PBS_JOBID
	cat $PBS_JOBNAME
	cat $PBS_QUEUE
	cat $PBS_NODEFILE

Then submit it with

	qsub env.job

Note that ncpus can not be larger than the number of processors on each node on the machine in question.

PBS Multiple Node Examples

This section gives various examples of requesting multiple nodes and ways of allocating the processors on these nodes (as many as possible on as few nodes as possible, scattered, random...) In many of the examples I use an interactive session (-I), because this makes it easier to show the different nodes allocated (using the cat $PBS_NODEFILE command). To submit a job submission file instead, leave out -I and add the name of the job submission file at the end.

4 nodes, 1 processor on each:

	$ qsub -q standby -I -l select=4:ncpus=1
	qsub: waiting for job 106336.steele-adm.rcac.purdue.edu to start
	qsub: job 106336.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a109
	steele-a136
	steele-a136
	steele-a136
	$ exit
	logout
	
	qsub: job 106336.steele-adm.rcac.purdue.edu completed
	$

Another attempt can give different nodes or the same:

	$ qsub -q standby -I -l select=4:ncpus=1
	qsub: waiting for job 453659.steele-adm.rcac.purdue.edu to start
	qsub: job 453659.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a187
	steele-a188
	steele-a208
	steele-a209
	$ exit
	logout
	
	qsub: job 453659.steele-adm.rcac.purdue.edu completed
	$

2 processors placed somewhere on 2 nodes. (Since"free" is the default, they will just be placed on any one or two available nodes, possibly while sharing with other jobs. It is not guaranteed to be on only one node ("pack"), or scattered across as many nodes as possible ("scatter"), and also not on one node without sharing with anyone else ("excl")):

	$ qsub -q standby -I -l select=2:ncpus=2
	qsub: waiting for job 106355.steele-adm.rcac.purdue.edu to start
	qsub: job 106355.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a117
	steele-a117
	$ exit
	logout
	
	qsub: job 106355.steele-adm.rcac.purdue.edu completed
	$

4 nodes, 1 processor on each node, placed anywhere:

	$ qsub -q standby -I -l select=4:ncpus=1 -l place=free
	qsub: waiting for job 106356.steele-adm.rcac.purdue.edu to start
	qsub: job 106356.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a097
	steele-a117
	steele-a117
	steele-a117
	$ exit
	logout
	
	qsub: job 106356.steele-adm.rcac.purdue.edu completed
	$

8 processors across 4 nodes, packed on as few nodes as possible:

	$ qsub -q standby -I -l select=4:ncpus=8 -l place=pack
	qsub: waiting for job 106356.steele-adm.rcac.purdue.edu to start
	qsub: job 106356.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a097
	steele-a117
	steele-a117
	steele-a117
	$ exit
	logout
	
	qsub: job 106356.steele-adm.rcac.purdue.edu completed
	$

Four processors for a four-rank message-passing program:

	$ qsub -I -l select=4
	qsub: waiting for job 439422.steele-adm.rcac.purdue.edu to start
	qsub: job 439422.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a100
	steele-a171
	steele-a171
	steele-a205
	$ exit
	logout
	qsub: job 439422.steele-adm.rcac.purdue.edu completed
	
	$

Notice that PBS placed two of the ranks on the same node. When these two ranks pass messages, the process will use direct memory access rather than message-passing. This is the same as place=free.

To request that the four ranks be on separate nodes:

	$ qsub -I -l select=4,place=scatter
	qsub: waiting for job 439423.steele-adm.rcac.purdue.edu to start
	qsub: job 439423.steele-adm.rcac.purdue.edu ready

	$ cat $PBS_NODEFILE
	steele-a100
	steele-a171
	steele-a205
	steele-a206
	$ exit
	logout
	qsub: job 439423.steele-adm.rcac.purdue.edu completed

	$

To request that four ranks be on a single node, we may pack them. We would want this if each rank does not use a lot of memory:

	$ qsub -I -l select=4,place=pack
	qsub: waiting for job 439600.steele-adm.rcac.purdue.edu to start
	qsub: job 439600.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a101
	steele-a101
	steele-a101
	steele-a101
	$ exit
	logout
	qsub: job 439600.steele-adm.rcac.purdue.edu completed
	
	$

The next examples uses program 'intro'.

place=scatter: PBS must attempt to place only 1 MPI rank on a node. Here, 8 MPI ranks on 8 nodes. (Note: by default, the node on which your processors are allocated may be shared by other jobs. To request exclusive access to nodes, you must either use "ncpus=" to request all of their processors or use the "place=excl" option):

Script:

	# PBS -l select=8,place=scatter,walltime=00:01:30
	mpiexec -n 8 ./intro

Output:

	R:0   Number of MPI ranks = 8
	
	R: 0     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 1     namelen:27  name:steele-a204.rcac.purdue.edu
	
	R: 2     namelen:27  name:steele-a244.rcac.purdue.edu
	
	R: 3     namelen:27  name:steele-a258.rcac.purdue.edu
	
	R: 4     namelen:27  name:steele-a259.rcac.purdue.edu
	
	R: 5     namelen:27  name:steele-a268.rcac.purdue.edu
	
	R: 6     namelen:27  name:steele-a270.rcac.purdue.edu
	
	R: 7     namelen:27  name:steele-a323.rcac.purdue.edu

place=free: PBS is free to place MPI ranks anywhere. Here, 8 MPI ranks on 3 nodes; nodes have 2 or 4 ranks.

Script:

	#PBS -l select=8,place=free,walltime=00:01:30
	mpiexec -n 8 ./intro

Output:

	R:0   Number of MPI ranks = 8
	
	R: 0     namelen:27  name:steele-a113.rcac.purdue.edu
	
	R: 1     namelen:27  name:steele-a113.rcac.purdue.edu
	
	R: 2     namelen:27  name:steele-a115.rcac.purdue.edu
	
	R: 3     namelen:27  name:steele-a115.rcac.purdue.edu
	
	R: 4     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 5     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 6     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 7     namelen:27  name:steele-a136.rcac.purdue.edu

place=pack: all chunks will be taken from one host. All 8 MPI ranks are packed on a single node.

Script:

	#PBS -l select=8,place=pack,walltime=00:01:30
	mpiexec -n 8 ./intro

Output:

	R:0   Number of MPI ranks = 8
	
	R: 0     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 1     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 2     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 3     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 4     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 5     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 6     namelen:27  name:steele-a474.rcac.purdue.edu
	
	R: 7     namelen:27  name:steele-a474.rcac.purdue.edu

Using the default case of place=. Here, 8 MPI ranks on 4 nodes; nodes have 1,2, or 3 ranks. Distribution of MPI ranks on nodes looks like place=free.

Script:

	#PBS -l select=8,walltime=00:01:30
	mpiexec -n 8 ./intro

Output:

	R:0   Number of MPI ranks = 8
	
	R: 0     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 1     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 2     namelen:27  name:steele-a136.rcac.purdue.edu
	
	R: 3     namelen:27  name:steele-a144.rcac.purdue.edu
	
	R: 4     namelen:27  name:steele-a144.rcac.purdue.edu
	
	R: 5     namelen:27  name:steele-a176.rcac.purdue.edu
	
	R: 6     namelen:27  name:steele-a176.rcac.purdue.edu
	
	R: 7     namelen:27  name:steele-a181.rcac.purdue.edu

This job was never run. PBS cannot pack all 16 chunks on one 8-core node of Steele.

Script:

	#PBS -l select=16,place=pack,walltime=00:01:30
	mpiexec -n 16 ./intro

By default, the node on which your processors are allocated may be shared by other jobs. To request exclusive access to nodes, you must either use "ncpus=" to request all of their processors or use the "place=excl" option:

	qsub –I –l select=1 –l place=excl

To explicitly ask to share a node with other jobs:

	qsub –I –l select=1 –l place=shared

Note that ncpus can not be larger than the number of processors on each node on the machine in question.

PBS Specific Types of Nodes Examples

We can request that a job be run on specific nodes. This can be done with the PBSPro 8.0 and newer "select=" syntax. It is useful for selecting nodes based on various quantities.

The select command can also be used to specify whether or not the processors you are asking for must be on the same nodes (i.e. if you are on a host that has nodes with two processors each and you want 4 processors for your job, then you can either (default) have both processors on two nodes or indicate that you do not care and perhaps get 4 processors on 4 different nodes.) If it is not important for your job that the processors are on the same nodes, then it is better to indicate that, since you might otherwise have to wait a long time for the whole nodes to be free.

Example Asking for only nodes with (at least) 2 GB memory (running interactively on 4 nodes):

	qsub -I -q standby -l select=4:mem=2gb

Example of how this is done:

	-bash-3.00$ qsub -I -q standby -l select=4:mem=2gb
	qsub: waiting for job 499333.steele-adm.rcac.purdue.edu to start
	qsub: job 499333.steele-adm.rcac.purdue.edu ready
	
	-bash-3.00$ cat $PBS_NODEFILE
	steele-a177
	steele-a181
	steele-a183
	steele-a189
	-bash-3.00$

PBS Interactive Job Examples

Running an interactive PBS job

They can be started with time constraints (walltime=hh:mm:ss) or without time constraints.

Note that running an interactive job without time constraints means that you will keep the nodes allocated for the default time limit for that queue. If this is shorter than the time you need, your job will not finish. If, on the other hand, it is longer than what you need, you are keeping those nodes from other people's usage. Therefore, use this with caution.

	$ qsub -I -q standby -l select=2:ncpus=2
	qsub: waiting for job 100.steele-adm.rcac.purdue.edu to start
	qsub: job 100.steele-adm.rcac.purdue.edu ready
	
	$

We then need to change to the directory where our program is located, and then just run it as you would otherwise. If you want to run a MPI-program, remember to type module load mpich2-intel, module load mpich2-gcc, or module load mpich2-pgi first. The program can then be run with mpirun or mpiexec.

Running an interactive PBS job and opening a display

	-bash-3.00$ qsub -I -q standby -l select=2:ncpus=2 -v DISPLAY
	qsub: waiting for job 301.venice-adm.rcac.purdue.edu to start
	qsub: job 301.venice-adm.rcac.purdue.edu ready
	
	-bash-3.00$

You can then run any program that is installed and which needs to open a display. You may need to load module <program> before you can run it. Again, always check module avail to see which programs can be accessed this way.

Note that ncpus can not be larger than the number of processors on each node on the machine in question.

Serial PBS Example

There are two ways to run a serial program under PBS: batch and interactively. For long jobs, batch submission is to be preferred. There is no difference in how you run a Fortran program, a C program or a C++ program, when they have been compiled.

Batch submission

Suppose that we want to run the C program 'hello.c' - where the executable is called 'hello'. Make a script and call it something meaningful, like run_hello. The script should then contain the following:

	#!/bin/bash
	cd $PBS_O_WORKDIR
	./hello

Since PBS will always start in your home directory, you should either do a cd $PBS_O_WORKDIR (which returns you to the directory you submitted the script from) or give the full path to the program.

The command to submit the job is the following:

	qsub -q standby -l select=1,walltime=1:00 run_hello

Where I am using the queue 'standby' on Steele, 1 node and a walltime of one min. My job submission file is called run_hello. It should be noted that if you want to use the default queue, you do not need to explicitly ask for it.

Submitting this script gives the following result. It will take a while before the job completes:

	$ qsub -q standby -l select=1,walltime=1:00 run_hello
	91.steele-adm.rcac.purdue.edu
	$

Doing a 'ls' in your directory will now show two new files:

	$ ls
	hello                            run_hello
	hello.c                          run_hello.e91
	hello.out                        run_hello.o91
	$

If everything went well, then the file 'run_hello.e91' will be empty, since it contains any error-messages your program gave while running. The file 'run_hello.o91' contains the output from your program. In this case the output is:

	$ cat run_hello.o91
	Hello World!
	$

Interactively

To use the PBS queue interactively, you must first give a command like the one below. Remember to type 'cd $PBS_O_WORKDIR' (or the path to the working directory), since you will have been returned to your home directory upon start of the interactive job.

$ qsub -I -q standby -l select=1
qsub: waiting for job 189639.steele-adm.rcac.purdue.edu to start
qsub: job 189639.steele-adm.rcac.purdue.edu ready

$

Where we are running in the queue 'standby' on Steele, and asking for 1 node.

We can now run the job the same way a serial job is normally run. Remember, interactive sessions are mostly for testing purposes, and longer jobs should always be submitted using a job submission file.

	$ ./hello
	Hello World!
	$

OpenMP PBS Example

To run an OpenMP program, set the environment variable OMP_NUM_THREADS to the desired number of threads, then enter the executable name and any necessary arguments at the shell prompt as with a serial program. If the OpenMP program is other than a short test program, then it should be run either as an interactive PBS job, or by submitting it with a job submission file.

In Csh:

	setenv OMP_NUM_THREADS <number of threads>

In Bash:

	export OMP_NUM_THREADS=<number of threads>

To see which compilers are available for OpenMP, see the section about compiling on Gold.

You should also set the environment variable PARALLEL to 1. This variable must be set or else any timers used by the program will return incorrect timings (see the etime man page for more details).

Click here to see an example of a Fortran 77 program with OpenMP commands (omp_hello_77.f). If you want to see an example of a C program with OpenMP commands (hello.c), then click here.

The compilers are installed and should be in your path. For threaded programs, try <program name>_r. (Example: xlf_r).

Language	Command
Fortran 77	xlf -qsmp=omp -qthreaded
Fortran 90	xlf90 -qsmp=omp -qthreaded
Fortran 95	xlf95 -qsmp=omp -qthreaded
C	cc -qsmp=omp -qthreaded
C++	xlC -qsmp=omp -qthreaded

Compiling the above mentioned example Fortran 77 program gives the following output when succesful:

-bash-3.00$ xlf -qsmp=omp -qthreaded omp_hello_77.f -o omp_hello_77
** hello   === End of Compilation 1 ===
1501-510  Compilation successful for file omp_hello_77.f.
-bash-3.00$

A compilation of the example C program gives the following (none) output when succesful:

	-bash-3.00$ cc -qsmp=omp -qthreaded omp_hello.c -o omp_hello
	-bash-3.00$

Running your program

There are two ways of running your OpenMP programs. If it is a short program you can just run it with ./program. If it is a longer program you should use the PBS queue. This can either be done interactively or by submitting a job using a job submission file. There is no difference in how you run a Fortran program, a C program or a C++ program, when they have been compiled.

Submitting the job to PBS using a script

To submit the job to PBS using a job submission file, you must first write the job submission file. Let us say that we want to run the C program example 'omp_hello.c'. Make a script and call it something meaningful, like run_hello. The script should then contain something like the following:

	cd $PBS_O_WORKDIR
	./omp_hello

Where 'PBS_O_WORKDIR' is a PBS-environment variable, which contains the name of the directory you were in when the job was submitted. You should thus submit the job from the directory where your program is located or give the absolute path to it in the script.

The command to submit a job is the following:

	qsub -q workq -l select=1:ncpus=2,walltime=1:00 run_program

Where the options used means the following:

-q <name>: tells which queue you want the job to run in (workq is the only queue and is thus the default). A list of available queues can be seen using the command qstat -Q.
-l select: tells the job how many nodes you want to use (1 processors in the example) and
ncpus: specifying the number of processes (tasks) to be run per node requested. Defaults to 1.
walltime=hh:mm:ss defines how much wall clock time it has (in the example it is set to 1 minute).

Submitting this script now gives the following result:

	qsub: job 121.gold.rcac.purdue.edu completed
	-bash-3.00$ qsub -q workq -l select=1:ncpus=2,walltime=1:00 run_hello
	122.gold.rcac.purdue.edu
	-bash-3.00$

Doing a 'ls' in your directory (after a while) will now show two new files:

	-bash-3.00$ ls
	hello                            run_hello
	hello.c                          run_hello.e121
	hello.out                        run_hello.o121
	-bash-3.00$

If everything went well, then the file 'run_hello.e121' will be empty, since it contains any error-messages your program gave while running. The file 'run_hello.o121' contains the output from your program. In this case the output is:

	-bash-3.00$ less run_hello.o121
	Thread 1 says: Hello World
	Thread 0 says: Hello World
	Thread 0 reports: the number of threads are 2
	-bash-3.00$

Running interactively

Use qstat -Q to see which queues are available on a given machine.

Example:

	qsub -I -q short -l select=2,walltime=8:00

Where the options used means the following:

-I means that we want to run the job interactively.
-q <name>: tells which queue you want the job to run in (workq is the only queue and it is thus default, so it is not really necessary). A list of available queues can be seen using the command qstat -Q.
-l select: tells the job how many chunks you want to use (2 in the example) and
walltime=hh:mm:ss defines how much wall clock time it has (in the example it is set to 8 minutes).

You can also just start up an interactive job without time constraints:

	qsub -I -q workq -l select=1:ncpus=2

(Where the options used mean we ask for 2 processors on each node - remember to check that the given machine has the number of processors on a node that you ask for). To end the job, you then type: exit.

Running the above PBS command gives:

	-bash-3.00$ qsub -I -q workq -l select=1:ncpus=2
	qsub: waiting for job 121.gold.rcac.purdue.edu to start
	qsub: job 121.gold.rcac.purdue.edu ready
	
	pbs_mom: run_pelog, set environment variable PBS_JOBDIR
	readline: warning: turning on OPOST for terminal
	readline: warning: turning on OPOST for terminal
	-bash-3.00$

We then need to change to the directory where our program is located. To run a program we just use ./program.

Example of running the compiled version of omp_hello.c:

	-bash-3.00$ qsub -I -q workq -l select=1:ncpus=2
	qsub: waiting for job 121.gold.rcac.purdue.edu to start
	qsub: job 121.gold.rcac.purdue.edu ready
	
	pbs_mom: run_pelog, set environment variable PBS_JOBDIR
	readline: warning: turning on OPOST for terminal
	readline: warning: turning on OPOST for terminal
	-bash-3.00$ cd openMP
	-bash-3.00$ ./omp_hello
	Thread 0 says: Hello World
	Thread 1 says: Hello World
	Thread 0 reports: the number of threads are 2
	-bash-3.00$

Note that the order of the processors is random. This can not be controlled in a parallel program.

If you want to see which nodes you are using, you can give the command:

	cat $PBS_NODEFILE

To stop running interactively, just type exit.

./program

If you have a short program and are just using ./program, then you need to tell the machine how many task processes you want. This can be done by setting the environment variable, as described in the beginning of this section. You can see the default with echo $OMP_NUM_THREADS.

Then you just run the program.

Here are an example (bash) of running the program omp_hello.c, for 2 threads, then 4 threads:

	-bash-3.00$ export OMP_NUM_THREADS=2
	-bash-3.00$ ./omp_hello
	Thread 0 says: Hello World
	Thread 1 says: Hello World
	Thread 0 reports: the number of threads are 2
	-bash-3.00$ export OMP_NUM_THREADS=4
	-bash-3.00$ ./omp_hello
	Thread 0 says: Hello World
	Thread 3 says: Hello World
	Thread 0 reports: the number of threads are 4
	Thread 1 says: Hello World
	Thread 2 says: Hello World
	-bash-3.00$

MPI PBS Example

The path to the MPI-compilers and programs to run, are already in your path. To compile your MPI-programs, use the IBM AIX compilers. They are installed for C, C++, and various versions of Fortran: mpcc/mpcc_r, mpCC/mpCC_r, mpxlf/mpxlf_r, mpxlf90/mpxlf90_r, and mpxlf95/mpxlf95_r.

To run your compiled MPI-programs, you can use either the Parallel Operating Environment (POE) or mpiexec. It should be noted that mpiexec just invokes poe. A shorter description of poe can be found in man poe.

The script mpiexec and poe should be run through a job submission file or interactively, if it is a long job or uses a lot of resources, it should always be run through a job submission file.

Instead of giving the number of task processes each time a program is run, they can also be set with the command:

(bash)

	export MP_PROCS=<# processes>

(tcsh)

	setenv MP_PROCS <# processes>

Using a job submission file

First you must write a job submission file. Let us say that we want to run the MPI/C program 'hello.c'. Make a script and call it something meaningful, like run_hello. The script should then contain something like the following:

	mpiexec -n 4 mpi/hello

You run the program with either poe or mpiexec. Since PBS will always start in your home directory, you should either give the full path to the program - here mpi/hello, or use the environment variable '$PBS_O_WORKDIR' (cd $PBS_O_WORKDIR).

The command to submit the job is the following:

	qsub -q workq -l select=4,walltime=2:00 run_hello

Where I am using the queue 'workq', 4 nodes and a walltime of 2 min. My job submission file is called run_hello. It is not really necessary to give the number of nodes to mpiexec in the job submission file, since I have already requested 4 nodes in the qsub command. When you have requested the number of nodes you wish to use through the qsub command, it is also possible to make a job submission file which only contains <path-to-file>/<filename>. This will run correctly.

Submitting a job submission file like the one shown above, gives the following result.

	-bash-3.00$ qsub -q workq -l select=4,walltime=2:00 run_hello
	124.gold.rcac.purdue.edu
	-bash-3.00$

124 is the job number given to this job.

It will take a while before the job is completed. Check for when two new files show up in your directory. Doing a ls in your directory will show that they are named as <jobscript>.e<jobnumber> and <jobscript>.o<jobnumber>.

	-bash-3.00$ ls
	hello                            run_hello
	hello.c                          run_hello.e124
	hello.out                        run_hello.o124
	-bash-3.00$

If everything went well, then the file 'run_hello.e124' will be empty, since it contains any error-messages your program gave while running. The file 'run_hello.o124' contains the output from your program. In this case the output is:

	-bash-3.00$ less run_hello.124
	Processor 2 of 4: Hello World!
	Processor 0 of 4: Hello World!
	Processor 1 of 4: Hello World!
	Processor 3 of 4: Hello World!
	-bash-3.00$

Running Interactively

Here is an example of running an MPI-program interactively. The test program is a C program called hello.c. First PBS is accessed interactively, here choosing 4 nodes and using the only queue 'workq'. Then we change directory to where our MPI-program is located (PBS always starts in your home directory). Next, the program is compiled (if this has not been done already), and then run with mpiexec or poe:

	-bash-3.00$ qsub -I -q workq -l select=4
	qsub: waiting for job 123.gold.rcac.purdue.edu to start
	qsub: job 123.gold.rcac.purdue.edu ready
	
	pbs_mom: run_pelog, set environment variable PBS_JOBDIR
	readline: warning: turning on OPOST for terminal
	readline: warning: turning on OPOST for terminal
	-bash-3.00$ cd mpi
	-bash-3.00$ mpcc hello.c -o hello
	-bash-3.00$ mpiexec -n 4 hello
	Processor 0 of 4: Hello World!
	Processor 1 of 4: Hello World!
	Processor 2 of 4: Hello World!
	Processor 3 of 4: Hello World!
	-bash-3.00$ poe hello -procs 4
	Processor 0 of 4: Hello World!
	Processor 1 of 4: Hello World!
	Processor 2 of 4: Hello World!
	Processor 3 of 4: Hello World!
	-bash-3.00$

Note that the order of the processors is random. This can not be controlled in a parallel program.

If you want to see which nodes you are using, you can give the command:

	cat $PBS_NODEFILE

To stop running interactively, just type exit.

Important notes

PBS Queues. Always use qstat -Q to determine which queues are available. The only queue currently available on Gold is 'workq'.

When using MPI_File_Write, the output to the file will be written in binary. To view it, use: od -d 'output.file'.

MPI_File_Write will not automatically delete the old contents of an output file, so you may have to remove it before writing new data to it, unless you want to keep the old data.

You can see which nodes you are using on one of the cluster machines with the command: cat $PBS_NODEFILE
Running a program with ./program is a bad idea, since it will just use one task process. So unless that is what you want (which is rarely the case for a MPI-program), you should use poe or mpiexec.
The order of the processors is random. There is no way to tell which processor will do what and in which order in a parallel program.

Common mistakes

For C programs, remember to write MPI_Send and MPI_Recv and NOT MPI_SEND and MPI_RECV. The compiler will not complain, but during the execution of the program you will get a very confusing error:

Invalid datatype (0) in MPI_Send, task 0...
In C programs, when sending arrays or values with MPI_Send/MPI_Scatter, you need to remember the & in front of the send/recieve buffer name. Example:
```
int array[5000];
int subarray[5000/4];
.
.
.
MPI_Scatter(&array,sendcount,MPI_INT,&subarray,recvcount,MPI_INT,\
0,MPI_COMM_WORLD);
```

In C programs, when using dynamically allocated arrays, they are really pointers. Therefore, when using the MPI_Send/MPI_Scatter, you must NOT put a & in front of the send/receive buffer name. Example:

int *array;
int *subarray;
.
.
.
array = (int *)malloc(array_size*sizeof(int));
subarray = (int *)malloc(subarray_size*sizeof(int));
.
.
.
MPI_Scatter(array,sendcount,MPI_INT,subarray,recvcount,MPI_INT,0,\
MPI_COMM_WORLD);

Remember that values must either be globally declared or sent/broadcast/scattered to every processor. Otherwise the other processor will not be able to see their values.

Also, remember that memory allocation must be done either globally or on each processor.

C/MPI programming examples

Most of the programs below are my answers to the exercises in the online "Introduction to MPI" course at NCSA.

hello.c: Each processor prints "Hello World" to the screen.

ping.c: Sending a message between processors 0 and 1. The program reports the initial values of inmsg and outmsg before sending and then after. Try running this program with 2, 3, and 4 processors and see that their order is random and that only processors 0 and 1 exchanges a value.

ArrayFindSerial.c: This is a serial program to find a target value in an array and report back the indices where that target value was found. The target value and the array is read from a file (data.dat below) and printed to an output file 'out.dat'. This serial program should just be run as ./program. It is included for comparison with the following parallel versions of the same program.

ArrayFindParallelChapter4.c: This is the first parallel version of the above serial program. I use the blocking MPI_Send and MPI_Recv. The Master processor reads the array in from the file. Then it divides it up in three equal parts and sends one to each slave processor. These (3) slave processors search through their subarray and finds the indices where the targetvalue are found. These indices are then converted to global indices and sent to the master processor. The master processor then assembles these and write them to a file. The program is meant to run on 4 task processes. I use a static size array, which is initialized in the beginning of the program.

ArrayFindParallelChapter5.c: This version still uses the blocking MPI_Send and MPI_Recv, but since I am now sending back both the index where the target value is found and the average of the index and the target value, I need to use a derived data type. This is first created and then used. The program runs on 4 task processes.

ArrayFindParallelChapter6.c: As in the last version, I create a derived data type, but I now use MPI_Bcast, MPI_Scatter, MPI_Barrier and MPI_Irecv. The program runs on 4 task processes.

ArrayFindParallelChapter7.c: I still use the derived data type and MPI_Bcast and MPI_Scatter, but I know also find the "neighbour processors" and have them send the first value of their subarray to each neighbour processor. The program uses 4 task processes.

ArrayFindParallelChapter8.c: Still using MPI_Bcast and MPI_Scatter. To accomplish finding the neighbour processor I this time create a topological ring, which is a much easier way of finding them.

ArrayFindParallelChapter9.c: Back to using the blocking MPI_Send and MPI_Recv again. This makes it easier to accomplish the goal of this program, which is to allow each of the 3 slave processors to write to the output file. The master processor (0) still reads from the input file.

ArrayFindParallelChapter12.c: I again use MPI_Bcast and MPI_Scatter. The arrays are no longer static and I allocate them dynamically when I know the length of the arrays. This value is read from the input file (b.dat).

data.dat: A file with the target value and array used by the 'ArrayFind' programs. The first value is the target value. All values are integers and separated by space.

b.dat: The input file used by the program 'ArrayFindParallelChapter12.c'. The value on the first line is the the number of elements in the array, the next line holds the target value to be found, and the following lines are the elements in the array. The values are all integers and they are separated by space.

Diagnostic Error messages from MPI

Click here and go to chapter 5 (p. 121) to see what the diagnostic error messages from MPI means.

PBS Hybrid Code Examples

To request a resource to run a hybrid job which uses two ranks for message-passing and eight threads of shared memory processing within each rank:

	$ qsub -I -l select=2:mpiprocs=1:ncpus=8
	qsub: waiting for job 439516.steele-adm.rcac.purdue.edu to start
	qsub: job 439516.steele-adm.rcac.purdue.edu ready
		
	$ cat $PBS_NODEFILE
	steele-a187
	steele-a188
	$ exit
	logout
		
	qsub: job 439516.steele-adm.rcac.purdue.edu completed	
	$

If a hybrid program uses a lot of memory and we cannot have eight threads on a node, we can request more nodes and fewer threads on each node. The argument scatter will attempt to place only one rank on a node:

	$ qsub -I -l select=4:mpiprocs=1:ncpus=4,place=scatter
	qsub: waiting for job 439593.steele-adm.rcac.purdue.edu to start
	qsub: job 439593.steele-adm.rcac.purdue.edu ready
	
	$ cat $PBS_NODEFILE
	steele-a121
	steele-a122
	steele-a125
	steele-a132
	$ exit
	logout
	
	qsub: job 439593.steele-adm.rcac.purdue.edu completed
	$

The following two examples are using this hybrid code.

Example, Request 2 MPI ranks each with 8 OpenMP threads. Request 2 chunks each having 1 MPI rank with 8 OpenMP threads.

Job submission file:

	#PBS -l select=2:mpiprocs=1:ncpus=8,walltime=0:30
	mpiexec -n 2 ./h

Output:

steele-a484
steele-a485

name:steele-a484.rcac.purdue.edu   M_ID:0  M_N:2
name:steele-a485.rcac.purdue.edu   M_ID:1  M_N:2
name:steele-a484.rcac.purdue.edu   M_ID:0  O_ID:0  O_P:8  O_T:1
name:steele-a485.rcac.purdue.edu   M_ID:1  O_ID:0  O_P:8  O_T:1

parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:0 i: 0
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:0 i: 1
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:1 i: 2
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:1 i: 3
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:2 i: 4
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:2 i: 5
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:3 i: 6
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:3 i: 7
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:4 i: 8
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:4 i: 9
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:5 i:10
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:6 i:12
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:6 i:13
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:5 i:11
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:7 i:14
parallel loop:   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:7 i:15

parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:0 i: 0
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:0 i: 1
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:1 i: 2
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:1 i: 3
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:2 i: 4
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:2 i: 5
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:3 i: 6
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:3 i: 7
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:4 i: 8
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:4 i: 9
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:5 i:10
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:5 i:11
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:6 i:12
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:6 i:13
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:7 i:14
parallel loop:   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:7 i:15

second serial region   name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:0 i=999
second serial region   name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:0 i=999
 
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=0
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=1
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=2
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=3
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=4
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=6
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=5
parallel region:       name:steele-a484.rcac.purdue.edu M_ID=0 O_ID=7

parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=0
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=1
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=2
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=3
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=4
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=5
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=6
parallel region:       name:steele-a485.rcac.purdue.edu M_ID=1 O_ID=7

third serial region    name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:0 i=999
third serial region    name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:0 i=999

name:steele-a484.rcac.purdue.edu M_ID:0 O_ID:0   Exits
name:steele-a485.rcac.purdue.edu M_ID:1 O_ID:0   Exits

Example

Job submission file:

	#PBS -l select=4:mpiprocs=1:ncpus=4,walltime=0:30
	mpiexec -n 4 ./h

Output:

steele-a355
steele-a002
steele-a027
steele-a028

name:steele-a355.rcac.purdue.edu   M_ID:0  M_N:4
name:steele-a355.rcac.purdue.edu   M_ID:0  O_ID:0  O_P:8  O_T:1
name:steele-a002.rcac.purdue.edu   M_ID:1  M_N:4
name:steele-a002.rcac.purdue.edu   M_ID:1  O_ID:0  O_P:8  O_T:1
name:steele-a027.rcac.purdue.edu   M_ID:2  M_N:4
name:steele-a027.rcac.purdue.edu   M_ID:2  O_ID:0  O_P:8  O_T:1
name:steele-a028.rcac.purdue.edu   M_ID:3  M_N:4
name:steele-a028.rcac.purdue.edu   M_ID:3  O_ID:0  O_P:8  O_T:1

parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0 i: 0
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0 i: 1
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0 i: 2
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0 i: 3
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:1 i: 4
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:1 i: 5
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:1 i: 6
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:1 i: 7
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:2 i: 8
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:2 i: 9
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:2 i:10
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:2 i:11
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:3 i:12
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:3 i:13
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:3 i:14
parallel loop:   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:3 i:15

parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0 i: 0
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0 i: 1
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0 i: 2
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0 i: 3
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:1 i: 4
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:1 i: 5
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:1 i: 6
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:1 i: 7
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:2 i: 8
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:2 i: 9
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:2 i:10
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:2 i:11
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:3 i:12
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:3 i:13
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:3 i:14
parallel loop:   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:3 i:15

parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0 i: 0
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0 i: 1
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0 i: 2
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0 i: 3
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:1 i: 4
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:1 i: 5
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:1 i: 6
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:1 i: 7
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:2 i: 8
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:2 i: 9
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:2 i:10
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:2 i:11
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:3 i:12
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:3 i:13
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:3 i:14
parallel loop:   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:3 i:15

parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0 i: 0
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0 i: 1
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0 i: 2
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0 i: 3
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:1 i: 4
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:1 i: 5
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:1 i: 6
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:1 i: 7
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:2 i: 8
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:2 i: 9
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:2 i:10
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:2 i:11
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:3 i:12
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:3 i:13
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:3 i:14
parallel loop:   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:3 i:15

second serial region   name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0 i=999
second serial region   name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0 i=999
second serial region   name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0 i=999
second serial region   name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0 i=999
 
parallel region:       name:steele-a355.rcac.purdue.edu M_ID=0 O_ID=0
parallel region:       name:steele-a355.rcac.purdue.edu M_ID=0 O_ID=1
parallel region:       name:steele-a355.rcac.purdue.edu M_ID=0 O_ID=2
parallel region:       name:steele-a355.rcac.purdue.edu M_ID=0 O_ID=3
parallel region:       name:steele-a002.rcac.purdue.edu M_ID=1 O_ID=0
parallel region:       name:steele-a002.rcac.purdue.edu M_ID=1 O_ID=1
parallel region:       name:steele-a002.rcac.purdue.edu M_ID=1 O_ID=2
parallel region:       name:steele-a002.rcac.purdue.edu M_ID=1 O_ID=3
parallel region:       name:steele-a027.rcac.purdue.edu M_ID=2 O_ID=0
parallel region:       name:steele-a027.rcac.purdue.edu M_ID=2 O_ID=1
parallel region:       name:steele-a027.rcac.purdue.edu M_ID=2 O_ID=2
parallel region:       name:steele-a027.rcac.purdue.edu M_ID=2 O_ID=3
parallel region:       name:steele-a028.rcac.purdue.edu M_ID=3 O_ID=0
parallel region:       name:steele-a028.rcac.purdue.edu M_ID=3 O_ID=1
parallel region:       name:steele-a028.rcac.purdue.edu M_ID=3 O_ID=2
parallel region:       name:steele-a028.rcac.purdue.edu M_ID=3 O_ID=3

third serial region    name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0 i=999
third serial region    name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0 i=999
third serial region    name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0 i=999
third serial region    name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0 i=999

name:steele-a355.rcac.purdue.edu M_ID:0 O_ID:0   Exits
name:steele-a002.rcac.purdue.edu M_ID:1 O_ID:0   Exits
name:steele-a027.rcac.purdue.edu M_ID:2 O_ID:0   Exits
name:steele-a028.rcac.purdue.edu M_ID:3 O_ID:0   Exits

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