High Performance Computing

1. System Access to QB4

1.1. SSH

To access QB4, users must connect using an Secure Shell (SSH) client.

Linux and Mac Users - SSH client is already installed and can be accessed from the command prompt using the ssh command. One would issue a command similar to the following:

$ ssh -X username@qbd.loni.org

The user would then be prompted for his password. The -X flags allow for X11 Forwarding to be set up automatically.

Windows Users - You will need to download and install a SSH client such as the PuTTY utility. If users need access to login with X11 Forwarding, a X-Server needs to be installed and running on your local Windows machine. Xming X Server is recommended, advanced users may also install Cygwin which also provides a command line ssh client similar to that available for Linux and Mac Users.

If you have forgotten your password, or you wish to reset it, see here(click "Forgot your password?").

Two-factor Authentication: To access QB-4, you need to set up two-factor authentication. Please follow the instructions here.

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1.2. Help

To report a problem please run the ssh or gsissh command with the "-vvv" option and include the verbose information in the ticket.

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2. File Transfer

2.1. SCP

Using scp is the easiest method to use when transferring single files.

Local File to Remote Host

% scp localfile user@remotehost:/destination/dir/or/filename

Remote Host to Local File

% scp user@remotehost:/remote/filename localfile

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2.2. SFTP

Interactive Mode

One may find this mode very similar to the interactive interface offered. A login session may look similar to the following:

% sftp user@remotehost
(enter in password)
 ...
sftp>

The commands are similar to those offered by the outmoded ftp client programs: get, put, cd, pwd, lcd, etc. For more information on the available set of commands, one should consult sftp the man page.

% man sftp

Batch Mode

One may use sftp interactively in two cases.

Case 1: Pull a remote file to the local host.

% sftp user@remotehost:/remote/filename localfilename

Case 2: Creating a special sftp batch file containing the set of commands one wishes to execute with out any interaction.

% sftp -b batchfile user@remotehost

Additional information on constructing a batch file is available in the sftp man page.

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2.3. rsync Over SSH (preferred)

rsync is an extremely powerful program; it can synchronize entire directory trees, only sending data about files that have changed. That said, it is rather picky about the way it is used. The rsync man page has a great deal of useful information, but the basics are explained below.

Single File Synchronization

To synchronize a single file via rsync, use the following:

To send a file:

% rsync --rsh=ssh --archive --stats --progress localfile \
        username@remotehost:/destination/dir/or/filename

To receive a file:

% rsync --rsh=ssh --archive --stats --progress \
        username@remotehost:/remote/filename localfilename

Note that --rsh=ssh is not necessary with newer versions of rsync, but older installs will default to using rsh (which is not generally enabled on modern OSes).

Directory Synchronization

To synchronize an entire directory, use the following:

To send a directory:

% rsync --rsh=ssh --archive --stats --progress localdir/ \
        username@remotehost:/destination/dir/ 

or

% rsync --rsh=ssh --archive --stats --progress localdir \
        username@remotehost:/destination 

To receive a directory:

% rsync --rsh=ssh --archive --stats --progress \
        username@remotehost:/remote/directory/ /some/localdirectory/

or

% rsync --rsh=ssh --archive --stats --progress \
        username@remotehost:/remote/directory /some/

Note the difference with the slashes. The second command will place the files in the directory /destination/localdir; the fourth will place them in the directory /some/directory. rsync is very particular about the placement of slashes. Before running any significant rsync command, add --dry-run to the parameters. This will let rsync show you what it plans on doing without actually transferring the files.

Synchronization with Deletion

This is very dangerous; a single mistyped character may blow away all of your data. Do not synchronize with deletion if you aren't absolutely certain you know what you're doing.

To have directory synchronization delete files on the destination system that don't exist on the source system:

% rsync --rsh=ssh --archive --stats --dry-run --progress \
        --delete localdir/ username@remotehost:/destination/dir/

Note that the above command will not actually delete (or transfer) anything; the --dry-run must be removed from the list of parameters to actually have it work.

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2.4. BBCP

Using BBCP to transfer large data files without encryption.

% bbcp [opt] user@source:/path/to/data user@destination:/path/to/store/data

Possible options include:

-P 2

Give a progress report every 2 seconds

- w 2M

TCP window size of 2MBytes

-s 16

Set the number of streams to 16 (default is 4)

Other options may be necessary if bbcp is not installed in a regular location on either end of the transfer. This can lead to rather complex command lines:

$ bbcp -z -T \
  "ssh -x -a -oFallBackToRsh=no %I -l %U %H /home/user/Custom/bin/bbcp" \
  foobar-5.4.14.tbz "ruser@10.20.30.40:foo.tbz"

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2.5 Client Software

scp and sftp

Standard Clients

The command-line scp and sftp tools come with any modern distribution of OpenSSH; this is generally installed by default on modern Linux, UNIX, and Mac OS X installs.

Windows Clients

Windows clients include:

• WinSCP,
• pscp & psftp

(puTTY-related command line utilities), and

• scp, sftp, & rsync as provided by Cygwin.

*** VERY IMPORTANT ***: if you use Filezilla, please use the Site Manager feature (under "File") to manage the profile of the cluster you use. In the "Transfer Settings" tab, make sure that the "Limit number of simultaneous comments" box is checked and the "Maximum number of connections" is set to 1. Failing to do so may result in Filezilla creating excessive ssh connections, which could lead the suspension of your user account.

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3. Computing Environment.

3.1. Shell

QB4's default shell is bash. Other shells are available: sh, csh, tcsh, and ksh. Users may change their default shell by logging into their LONI Profile page at https://allocations.loni.org.

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The following is a guide to managing your software environment with modules.

The Environment Modules package provides for dynamic modification of your shell environment. Module commands set, change, or delete environment variables, typically in support of a particular application. They also let the user choose between different versions of the same software or different combinations of related codes. Complete documentation is available in the module(1) and modulefile(4) manpages.

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3.2.1. Default Environment

The default environment is defined in the .modules file under each user's home directory. Edit this file if you would like to change the default environment.

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3.2.2. Useful Module Commands

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3.2.3. Loading and unloading modules

You must remove some modules before loading others. Some modules depend on others, so they may be loaded or unloaded as a consequence of another module command. For example, if intel and mvapich are both loaded, running the command module unload intel will automatically unload mvapich. Subsequently issuing the module load intel command does not automatically reload mvapich.

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4. File Systems

User-owned storage on the QB4 system is available in two directories: home (/home/<your user name>) and work (/work/<your user name>). These directories are on separate file systems, and accessible from any node in the system. The work directory is created automatically within an hour of first login. If your work directory does not exist when you login, please wait at least an hour before contacting the HPC helpdesk.

4.1. Home Directory

The /home file system quota on QB4 is 10 GB. Files can be stored on /home permanently, which makes it an ideal place for your source code and executables. The /home file system is meant for interactive use such as editing and active code development. Do not use /home for batch job I/O.

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4.2. Work (Scratch) Directory

The /work (/scratch) directories are created automatically once an hour after first login. The /work volume is meant for the input and output of executing batch jobs and not for long term storage. We expect files to be moved off to other locations or deleted in a timely manner, usually within 30-120 days. For performance reasons, our policy on all volumes is to limit the number of files per directory to around 10,000 and total number files to about 500,000.

The /work file system quota on QB4 is unlimited. If it becomes over utilized we will enforce a purge policy, which means that we will begin deleting files starting with the oldest last accessed date, and largest files, and continue until the volume has been reduced below 80%. An email message will be sent out weekly to users who may have files subject to purge informing them of their /work utilization. If diskspace should become critically low, more drastic measures may be required to keep the system stable.

Please do not attempt to circumvent the removal process by manually changing file dates. The /work volume capacity is not unlimited, and attempts to circumvent the purge process may adversely affect others and lead to access restrictions to the /work volume or even the cluster.

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5. Application Development

The Intel, GNU and Portland Group (PGI) C, C++ and Fortran compilers are installed on QB4 and they can be used to create OpenMP, MPI, hybrid and serial programs. The commands you should use to create each of these types of programs are shown in the table below.

Intel compilers are loaded by default, codes can be compiled according to the following chart:

Default MPI: Intel MPI 2021.5.1 compiled with Intel compiler version 2021.5.0

To compile a serial program, the syntax is: <your choice of compiler> <compiler flags> <source file name> . For example, the command below compiles the source file mysource.f90 and generate the executble myexec.

$ ifort -o myexec mysource.f90

To compile a MPI program, the syntax is the same, except that one needs to replace the serial compiler with an MPI one listed in the table above:

$ mpif90 -o myexec_par my_parallel_source.f90

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module load cuda

nvcc -arch=compute_20 -code=sm_20 ...

module load pgi

pgcc -acc -ta=nvidia -Minfo=accel code.c -o code.exe

6. Running Applications

QB4 uses SLURM to manage user jobs. Whether you run in batch mode or interactively, you will access the compute nodes using the SLURM command as described below. Remember that computationally intensive jobs should be run only on the compute nodes and not the login nodes. More details on submitting jobs and SLURM commands can be found here.

6.1. Available Partitions (Queues) on QB4

Below are the possible job queues to choose from:

• single - Used for jobs that will only execute on a single node, i.e. nodes=1:ppn<=64.
• workq - Used for jobs that will use at least one node, i.e. nodes>=1:ppn=64. Currently, this queue has a wallclock limit of 72 hours (3 days). Jobs in workq are not preemptable, which means that running jobs will not be disrupted before completion.
• checkpt - Used for jobs that will use at least one node. Jobs in the checkpt queue can be preempted if needed.
• bigmem - Used for jobs that want to use the 2 TB nodes. This queue has a wallclock limit of 72 hours (3 days).
• gpu2 - Used for jobs that run applications that are capable for utilizing the Nvidia GPUs on the 2-GPU compute nodes.
• gpu4 - Used for jobs that run applications that are capable for utilizing the Nvidia GPUs on the 4-GPU compute nodes.

The available queues and actual limit settings can be verified by running the command:

sinfo -s

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6.2. Job Submission

SLURM (Simple Linux Utility for Resource Management) is an open source, highly scalable cluster management and job scheduling system. It is used for managing job scheduling on new HPC and LONI clusters. It was originally created at the Livermore Computing Center, and has grown into a full-fledge open-source software backed up by a large community, commercially supported by the original developers, and installed in many of the Top-500 supercomputers.

Information about the following topics can be found here:

• Submitting batch script (single node)
• Submitting batch script (multiple nodes)
• Submitting interactive jobs
• Jobs Using GPUs
• Commonly used SLURM Commands

Submitting batch script (single node)

To create a batch SLURM script, use your favorite editor (e.g. vi or emacs) to create a text file with both SLURM instructions and commands how to run your job. All SLURM directives (special instructions) are prefaced by the #SBATCH. Below is an example of a SLURM batch job script:

 #!/bin/bash
 #SBATCH -N 1               # request one node
 #SBATCH -t 2:00:00	        # request two hours
 #SBATCH -p single          # in single partition (queue)
 #SBATCH -A your_allocation_name
 #SBATCH -o slurm-%j.out-%N # optional, name of the stdout, using the job number (%j) and the hostname of the node (%N)
 #SBATCH -e slurm-%j.err-%N # optional, name of the stderr, using job and hostname values
 # below are job commands
 date

 # Set some handy environment variables.

 export HOME_DIR=/home/$USER/myjob
 export WORK_DIR=/work/$USER/myjob
 
 # Make sure the WORK_DIR exists:
 mkdir -p $WORK_DIR
 # Copy files, jump to WORK_DIR, and execute a program called "mydemo"
 cp $HOME_DIR/mydemo $WORK_DIR
 cd $WORK_DIR
 ./mydemo
 # Mark the time it finishes.
 date
 # exit the job
 exit 0

To submit the above job to the scheduler, save the above script as a text file, e.g., singlenode.sh, then use the below command to submit:

$ sbatch singlenode.sh

List of useful SLURM directives and their meaning:

• #SBATCH -A allocationname: short for --account, charge jobs to your allocation named allocationname.
• #SBATCH -J: short for --jobname, name of the job.
• #SBATCH -n : short for --ntasks, number of tasks (CPU cores) to run job on. The memory limit for jobs is 4 GB of MEM per CPU core requested.
• #SBATCH -N : short for --nodes, number of nodes on which to run.
• #SBATCH -c : short for --ncpus-per-task, number of threads per process.
• #SBATCH -p partition: short for --partition, submit job to the partition queue.
  • Allowed values for partition: single, checkpt, workq, gpu, bigmem.
  • Depending on cluster, addition partitions can be found via the sinfo command.
• #SBATCH -t hh:mm:ss: short for --time, request resources to run job for hh hours, mm minutes and ss seconds.
• #SBATCH -o filename.out: short for --output, write standard output to file filename.out.
• #SBATCH -e filename.err: short for --error, write standard error to file filename.err.
  • Note that by default, SLURM will merge stardard error and standard output to one file if no "-o" or "-e" flag is set.
• #SBATCH --mail-user your@email.address: Address to send email to when the --mail-type directive below is trigerred.
• #SBATCH --mail-type type: Send an email after job status typeoccurs. Common values for type include BEGIN, END, FAIL or ALL. The arguments can be combined, for e.g. BEGIN, END will send email when job begins and ends

List of common useful SLURM environmental variables and their meaning:

• SLURM_JOBID: Job ID number given to this job
• SLURM_JOB_NODELIST: List of nodes allocated to the job
• SLURM_SUBMIT_DIR: Directory where the sbatch command was executed
• SLURM_NNODES: Total number of nodes in the job's resource allocation.
• SLURM_NTASKS: Total number of CPU cores requested in a job.

Submitting batch script (multiple nodes)

Creating multiple-node job script is very similar to the single node job script, with the difference of using multiple nodes. Below is an example of a multiple-node batch job script:

 #!/bin/bash
 #SBATCH -N 2                	# request two nodes
 #SBATCH -n 16 		       	# specify 16 MPI processes (8 per node)
 #SBATCH -c 6			# specify 6 threads per process
 #SBATCH -t 2:00:00
 #SBATCH -p checkpt
 #SBATCH -A your_allocation_name
 #SBATCH -o slurm-%j.out-%N # optional, name of the stdout, using the job number (%j) and the first node (%N)
 #SBATCH -e slurm-%j.err-%N # optional, name of the stderr, using job and first node values
 # below are job commands
 date

 # Set some handy environment variables.

 export HOME_DIR=/home/$USER/myjob
 export WORK_DIR=/work/$USER/myjob
 
 # load appropriate modules, in this case Intel compilers, MPICH
 module load mpich/3.1.4/INTEL-15.0.3
 # Make sure the WORK_DIR exists:
 mkdir -p $WORK_DIR
 # Copy files, jump to WORK_DIR, and execute a program called "my_mpi_demo"
 cp $HOME_DIR/mydemo $WORK_DIR
 cd $WORK_DIR
 srun -N2 -n8 -c6 /my_mpi_demo # Launch the MPI application with two nodes, 8 MPI processes each node, and 6 threads per MPI process.
 # Mark the time it finishes.
 date
 # exit the job
 exit 0

Note: in the examples above, the srun command is used to launch the MPI application. This will be the default behavior.

The syntax for the srun command is:

srun <flags> <name of the MPI executable>

Some useful flags are:

• -N: number of nodes
• -n: total number of MPI processes
• -c: number of threads per MPI process
• -u: turn on unbuffered output (the output from MPI processes will be flushed to stdout as soon as it's generate); without this flag, Slurm will buffer and rearrange the output according to the MPI ranks.

Submitting interactive jobs

To start an interactive job, use the salloc command similar to the example below:

 salloc -t 1:00:00 -n8 -N1 -A your_allocation_name -p single

Similar to the batch job script, the -n denotes 8 tasks (cores), the -N denotes 1 compute node. The complete form of the above command can be:

 salloc --time=1:00:00 --ntasks=8 --nodes=1 --account=your_allocation_name --partition=single

Note:

• If an interactive job session is submitted to a partition other than single, the -n or --ntasks flag will be ignored and one or more entire nodes will be allocated to the job.
• Our recommendation is to specify your allocation name (-A your_allocation_name) to the salloc command so a proper allocation can be used by the scueduler.

Jobs Using GPUs

For jobs using GPUs, the number of GPU devices must be explicitly specified using the “--gres=gpu:” flag.

Requesting One GPU

If a job cannot use multiple GPU devices efficiently or if running a test job, a user should request one GPU. In this case, The job will share a node with other jobs.

For an interactive session requesting one GPU:

salloc -t hh:mm:ss -N1 -n16 --gres=gpu:1 -p gpu_partition_name -A your_allocation_name 

For a batch job requesting one GPU:

#!/bin/bash
#SBATCH -N 1
#SBATCH -n 16
#SBATCH -t hh:mm:ss
#SBATCH -p gpu_partition_name
#SBATCH --gres=gpu:1
#SBATCH -A your_allocation_name

commands to run

Please note that the valid values for the number of tasks ("-n") is between 1 and (total number of CPU cores on the node)/(total number of GPUs on the node). For instance, if a job request one GPU on a node with 64 cores and 4 GPUs, the valid value for "-n" is from 1 to 64/4=16.

Requesting More Than One GPU (But Less Than A Node)

Users can request more than one GPU on a node (e.g. 2 or 3 GPUs on a node with 4 GPUs). In this case, The job will also share a node with other jobs.

For an interactive session requesting multiple GPUs:

salloc -t hh:mm:ss -N1 -n32 --gres=gpu:2 -p gpu_partition_name -A your_allocation_name

For a batch job requesting multiple GPUs:

#!/bin/bash
#SBATCH -N 1
#SBATCH -n 32
#SBATCH -t hh:mm:ss
#SBATCH -p gpu_partition_name
#SBATCH --gres=gpu:2
#SBATCH -A your_allocation_name

commands to run

Please note that the valid values for the number of tasks ("-n") is between 1 and (number of GPU requested)*(total number of CPU cores on the node)/(total number of GPUs on the node). For instance, if a job request 2 GPUs on a node with 64 cores and 4 GPUs, the valid value for "-n" is from 1 to 2*64/4=32.

Requesting One GPU Node With All Its GPUs

For an interactive session requesting one GPU node with all its GPUs (either 2 or 4, depending on the node configuration):

salloc -t hh:mm:ss -N1 -n64 --gres=gpu:number_of_gpus -p gpu_partition_name -A your_allocation_name 

For a batch job requesting one GPU node and all its GPUs:

#!/bin/bash
#SBATCH -N 1
#SBATCH -n 64
#SBATCH -t hh:mm:ss
#SBATCH -p gpu_partition_name
#SBATCH --gres=gpu:number_of_gpus
#SBATCH -A your_allocation_name

commands to run

Requesting Multiple GPU Nodes With All Their GPUs

For an interactive session requesting multiple GPU nodes with all their GPUs (either 2 or 4, depending on the node configuration):

salloc -t hh:mm:ss -N number_of_gpu_nodes --gres=gpu:number_of_gpus -p gpu_partition_name -A your_allocation_name

For a batch job requesting multiple GPU nodes with all their GPUs:

#!/bin/bash
#SBATCH -N number_of_gpus_nodes
#SBATCH -t hh:mm:ss
#SBATCH -p gpu_partition_name
#SBATCH --gres=gpu:number_of_gpus
#SBATCH -A your_allocation_name

commands to run

Please note that, the value of "number_of_gpus" is the number of GPUs PER NODE, not the total number of GPUs that will be allocated to the job. For instance, when requesting 2 nodes with 4 GPUs on each node, the flag should be "--gres=gpu:4".

Commonly used SLURM Commands

• squeue is used to show the partition (queue) status. Useful options:
  • -l ("l" for "long"): gives more verbose information
  • -u someusername: limit output to jobs by username --state=pending: limit output to pending (i.e. queued) jobs --state=running: limit output to running jobs

  Below is an example to query all jobs submitted by current user (fchen14)

  [fchen14@qbd2 ~]$ squeue -u $USER
       JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
         340   checkpt     bash  fchen14  R    1:06:59      1 qbd002
         339   checkpt     bash  fchen14  R    1:07:09      1 qbd001
  

• sinfo is used to view information about SLURM nodes and partitions. Typical usage:

  [fchen14@qbd001 test]$ sinfo
  PARTITION AVAIL  TIMELIMIT  NODES  STATE NODELIST
  debug        up   infinite      3   idle qbd[026-027,032]
  checkpt*     up 3-00:00:00      2  alloc qbd[001-002]
  checkpt*     up 3-00:00:00     23   idle qbd[003-025]
  single       up 7-00:00:00      2  alloc qbd[001-002]
  single       up 7-00:00:00     23   idle qbd[003-025]
  bigmem       up 7-00:00:00      2   idle qbd[033-034]
  

• scancel is used to signal or cancel jobs. Typical usage with squeue:

  [fchen14@qbd1 ~]$ squeue -u fchen14
               JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
                 341   checkpt     bash  fchen14  R       0:13      1 qbd001
                 340   checkpt     bash  fchen14  R    1:50:57      1 qbd002
  # cancel (delete) job with JOBID 340			   
  [fchen14@qbd1 ~]$ scancel 340
  # job status might display a temporary "CG" ("CompletinG") status immediately after scancel
  [fchen14@qbd1 ~]$ squeue -u fchen14 
               JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
                 340   checkpt     bash  fchen14 CG    1:51:08      1 qbd002
                 341   checkpt     bash  fchen14  R       0:41      1 qbd001
  [fchen14@qbd1 ~]$ squeue -u fchen14 
               JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
                 341   checkpt     bash  fchen14  R       1:08      1 qbd001
  

• scontrol is used to view or modify SLURM configuration and state. Typical usage for the user is to check job status:

  [fchen14@qbd1 ~]$ squeue -u fchen14 # show all jobs
               JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
                 341   checkpt     bash  fchen14  R    1:29:20      1 qbd001
  [fchen14@qbd1 ~]$ scontrol show job 341
  JobId=341 JobName=bash
     UserId=fchen14(32584) GroupId=Admins(10000) MCS_label=N/A
     Priority=1 Nice=0 Account=hpc_hpcadmin6 QOS=normal
     JobState=RUNNING Reason=None Dependency=(null)
     Requeue=1 Restarts=0 BatchFlag=0 Reboot=0 ExitCode=0:0
     RunTime=01:29:31 TimeLimit=12:00:00 TimeMin=N/A
     SubmitTime=2020-05-07T10:47:52 EligibleTime=2020-05-07T10:47:52
     AccrueTime=Unknown
     StartTime=2020-05-07T10:47:52 EndTime=2020-05-07T22:47:57 Deadline=N/A
     SuspendTime=None SecsPreSuspend=0 LastSchedEval=2020-05-07T10:47:52
     Partition=checkpt AllocNode:Sid=qbd1:28374
     ReqNodeList=(null) ExcNodeList=(null)
     NodeList=qbd001
     BatchHost=qbd001
     NumNodes=1 NumCPUs=8 NumTasks=1 CPUs/Task=1 ReqB:S:C:T=0:0:*:*
     TRES=cpu=8,mem=22332M,node=1,billing=8
     Socks/Node=* NtasksPerN:B:S:C=0:0:*:* CoreSpec=*
     MinCPUsNode=1 MinMemoryNode=22332M MinTmpDiskNode=0
     Features=(null) DelayBoot=00:00:00
     OverSubscribe=NO Contiguous=0 Licenses=(null) Network=(null)
     Command=/bin/bash
     WorkDir=/home/fchen14/test
     Power=
  

More detailed information on the SLURM commands to schedule and monitor jobs can be found at Slurm on-line documentation.

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