Quick Start Guide

Detailed below are common methodologies and good practices for access and using the CRC’s resources.

Cluster Computing Format

The organization of a super-computer or cluster is quite different from traditional desktop computing. Instead of all commands executing on the machine in front of you, everything is executed on a remote server, at times with no user interaction. A typical connection will look like:

                                                 Cluster
                                         +---+---+---+---+---+---+
               +---->+-------+           |   |   |   |   |   |   |
               |     | Front |           |   |   |   |   |   |   |
               |     |  End  |           |   |   |   |   |   |   |
               |     +---+---+           |   |   |   |   |   |   |
Internet       |         |               +---+---+-------+---+---+
Connection     |         |                           ^
               |         |                           |
               |         +---------------------------+
           ____|______
           \+--+------+
           \|Personal |
           \|Computer |
           \+---------+

To access the CRC infrastructure, you will connect to a Front end or Head node where you can prepare, submit, check on, and delete your batch jobs. Most jobs executed on CRC servers are batch jobs, which are non-interactive well-defined jobs which are queued and executed on a compute host when resources are available.


Front End Systems

Note

For users connecting from off campus, please review the section Connecting from off campus first.

In order to submit and run jobs on CRC servers, the first step is to connect to a front end machine. This machine will facilitate connections to the job manager which will handle your job from submission to execution.

The CRC provides the following front-end machines for compilation and job submission. Each machine is configured with identical software stacks.

  • crcfe01.crc.nd.edu (2 12 core Intel(R) Haswell processors with 256 GB RAM)

  • crcfe02.crc.nd.edu (2 12 core Intel(R) Haswell processors with 256 GB RAM)

  • crcfeIB01.crc.nd.edu (4 16 core 2.4 GHz AMD Opteron processors with 512 GB RAM)

Warning

Front-Ends are NOT for large long running (>1hr) jobs. For such jobs please using the queuing system and compute nodes. Any long running on a public front end machine may be killed.

To see how to connect to a front end from your favorite OS, see Connecting to CRC Servers.


Proper Front End Usage

The front end machines are the interface to the the rest of the computing resources of the CRC. There are both faculty owned and public front ends, the majority of information found here will pertain to public front ends. The public front ends are shared by all of campus and external collaborators to perform a wide variety of tasks related to research.


Logging in

There are 2 general access front ends available.

crcfe01.crc.nd.edu
crcfe02.crc.nd.edu

The primary interface to these machines is through SSH. To connect to either of these machines, you’d start either a terminal (Mac and Linux) or an ssh client on Windows. For Windows we recommend MobaXterm. You’d then either follow the instructions on the ssh client or enter the following command in a terminal, replacing “X” with the desired machine (1 or 2) and replacing “netid” with your Notre Dame NetID:

ssh netid@crcfe0X.crc.nd.edu

If you are having troubles logging in and have a new account, be sure to read the welcome email which was sent on the activation of your CRC account:

  • First login to okta.nd.edu.

  • If you continue to have trouble logging in:

    • Check all spelling

    • Be sure your ssh client and OS are updated/patched.

If all else fails, notify us via email at CRCSupport@nd.edu and please provide the following details:

  • ND netid

  • Which machine you’re trying to connect to

  • Your computer’s Operating System (Windows, Mac, Linux, etc)

  • The ssh client you’re using (Putty, MobaXterm, terminal, etc).

Note

If you intend on using HTCondor for job submissions, the front end machine to connect to is condorfe.crc.nd.edu If you need to compile code with infiniband support, connect to crcfeib01.crc.nd.edu.


Utilizing Front Ends

Once connected to a front end, you may begin preparing jobs for submission to either UGE or HTCondor (on condorfe.crc.nd.edu). There are a few important notes about operating within the front end environment:

  • There will be other users connected to this machine, any disruptive behaviour will be addressed.

  • Any task / process running longer than 1 (ONE) hour may be removed / killed by an administrator. Submit long running jobs to the batch system.

  • Do not launch large mpi or smp processes on a front end.

  • Front ends could be used for small debugging, if you have a job which requires more resources to be debugged submit it as a UGE job to the debug queue.

    • More information on the queues and UGE can be found on the UGE Environment page.

  • When logged in, you will be within your user AFS space. Initially, there will be a few directories there. DO NOT remove your Public directory, this contains important login scripts.

  • The default shell is BASH. If you have an older account, your login shell may be tcsh. If you’d like to request bash as your default, email CRCSupport@nd.edu.

  • Software which is not included in an install of RHEL, can be accessed through the Modules.

  • Small processing which is not disruptive/resource intensive can be done on the front ends. This is normally pre-processing or post-processing after completion of UGE jobs.

  • All CRC systems are a Linux variant. For tip on Linux commands, see Linux Coding Cheat Sheet


For submitting jobs to UGE, please see Submitting Batch Jobs. More sample scripts/submissions can normally be found on a module/software’s page. Search for the module in question in the search bar on the top left of the page.

Available Software

The software environment on CRC servers is managed utilizing Modules. A module is a an easy way to manage the necessary environmental paths and changes to utilize different pieces of software. You can easily modify your programming and/or application environment by simply loading and removing the required modules. The most common module commands are:

module avail

module list

module load module_name

More information on the CRC Modules can be found on the Modules page.


File Systems

The CRC provides two complimentary file systems for storing programs and data.

AFS

  • Distributed file system

  • Initial 100GB allocation

  • Longer-term storage; backup taken daily

  • User file system, your home directory lives here

  • You can check your current AFS usage with the following command:

quota

Panasas

  • High-performance parallel file system

  • To obtain an allocation on /scratch365, send us a request at CRCSupport@nd.edu.

  • Used for runtime working storage; no backup, purged yearly.

  • You can check your current /scratch365 usage with the following command:

pan_df –H /scratch365/netid

Further info: Storage


File Transfers

To transfer files from your local desktop MacOS filesystem to your CRC filesystem space we recommend installing and using the following file transfer (GUI) client: Cyberduck

For Windows users, we recommend using MobaXterm as both an SSH client and a file transfer client.

If you would like to transfer data between the CRC servers and Google Drive, we recommend the Rclone tool.


Job Scripts

A typical batch job is a simple script which contains the commands necessary to execute the job which needs to be accomplished whether this is an R, Matlab, or Python script or a compiled executable.

Jobs are submitted to the compute nodes via the Univa Grid Engine (UGE) batch submission system. Basic UGE batch scripts should conform to the following template:

#!/bin/bash

#$ -M netid@nd.edu   # Email address for job notification
#$ -m abe            # Send mail when job begins, ends and aborts
#$ -pe mpi-24 24     # Specify parallel environment and legal core size
#$ -q long           # Specify queue
#$ -N job_name       # Specify job name

module load xyz      # Required modules

mpirun -np $NSLOTS ./app # Application to execute

Further info: Submitting Batch Jobs


Parallel Environments

To use more than one core in a job, you must specify a parallel environment. A parallel environment is a way to specify whether to use multiple cores on one machine or to use multiple nodes (more than 1 server). The two parallel environments are below.

P.E. name

Valid Core counts

Example

Targeted machines

smp

1, 2, 3, … N

smp 8

any node

mpi-24

24, 48, 72, …

mpi-24 48

d12chasXXX

mpi-48

48, 96, 144, …

mpi-48 96

d24cepycXXX

mpi-64

64, 128, 192, . .

mpi-64 192

q16coptXXX

Note

  • If no parallel environment is requested (i.e. you do not specify a -pe parameter), then the default execution environment is a single-core serial job.

  • Every machine has one thread per core!

Further info: UGE Environment


Queues

CRC provides two general-purpose queues for the submission of jobs (using the -q parameter):

Below you’ll find a summarization of the available queues.

Queue Name

Purpose

Run time Limit

Example machines

long

Long running jobs

14 days*

d12chasXXX

debug

Quick testing / debugging

4 hours

d12chasXXX

gpu

Long running GPU jobs

7 days*

qa-titanx-001

gpu-debug

Quick testing / debugging GPU jobs

4 hours

da-1080-002

Note

In the above table, the long queue and gpu queue can include any faculty / lab owned machines you have access to. The runtime limit and example machines will most likely be different from the table above. Speak to your lab-mates, PI, or email us at CRCSupport@nd.edu if you’d like to know specifics of those machines.

If you wish to target a specific architecture for your jobs, then you can specify a host group instead of a general-purpose queue.


Host Groups

If you wish to target machines in a finer granularity than queues, there are host groups. For example, the general access machines are the “@crc_d12chas” host group. If your research lab or faculty advisor has purchased a machine(s), there is most likely a host group you can target.

Monitoring the status and availability of resources at a glance can be done with the free_nodes.sh script.

free_nodes.sh -G              # For general access
free_nodes.sh -D              # For Debug nodes
free_nodes.sh @crc_d12chas    # You can target host groups

For further resource monitoring, consult the help information: free_nodes.sh --help


Job Submission and Monitoring

Job scripts can be submitted to the SGE batch submission system using the qsub command:

qsub job.script

Once your job script is submitted, you will receive a numerical job id from the batch submission system, which you can use to monitor the progress of the job.

Job scripts that are determined by UGE to have made valid resource requests will enter the queuing system with a queue-waiting qw status (once the requested resources become available, the job will enter the running (r) status). Job scripts that are determined not to be valid will enter the queuing system with an error queue-waiting (Eqw) status.

To see the status of your job submissions, use the qstat command with your username (netid) and observe the status column:

qstat –u username

For a complete overview of your job submission, invoke the qstat command with the job id:

qstat –j job_id

To see all pending and running jobs, simply type qstat without any options

qstat

The main reasons for invalid job scripts (i.e. having Eqw status) typically are:

  • Illegal specification of parallel environments and/or core size requests

  • Illegal queue specification

  • Copying job scripts from a Windows OS environment to the Linux OS environment on the front-end machines (invisible Windows control code-blocks are not parsed correctly by UGE). This can be fixed by running the script through the dos2unix command

Why is my job waiting in the Queue?

The first reason a job could be waiting in a queue is simply because there are no resources available yet for your job to begin running. Note that for the most part (especially if you are using the general access machines), you are sharing resources with every other CRC user.

The first item to check if if there are available resources at the moment for your job, you can use the free_nodes.sh script to check, for example:

free_nodes.sh -G

Note that even if there resource shown as available, the scheduler could be freeing up space for a larger job with higher priority than yours. There is also a maximum number of concurrent jobs to avoid overloading the systems with one person’s jobs, this number fluctuates during the year depending on system utilization.

  • If you need to push a large amount of jobs consisting of less than 4 cores each, perhaps HTCondor is a good fit for you.

Parallel Jobs

If you requested a parallel environment with your job, be sure that requested environment adheres to the target resources.

For example, be sure the machines you’re targeting through smp can support the number of cores requested, a request of smp 25 will never be served on the general access or @crc_d12chas host group.

If you’re requesting an mpi-X Y environment, be sure the Y value is a multiple of X, and be sure X is a valid number for the targeted machines. For example, mpi-24 48 is the correct requested environment of 2 machines out of the general access queue.


Job Deletion

To delete a running or queued (e.g. submissions with Eqw status) job, use the following command:

qdel –j job_id

Job Resource Monitoring

To better understand the resource usage (e.g. memory, CPU and I/O utilization) of your running jobs, you can monitor the runtime behavior of your job’s tasks as they execute on the compute nodes.

To determine the nodes on which your tasks are running, enter the following qstat command along with your username. Record the machine names (e.g. d12chas400.crc.nd.edu) associated with each task (both MASTER and SLAVE):

qstat -u username -g t

There are two methods for analyzing the behavior of tasks (once you have a machine name):

  • Xymon GUI Tool (detailed breakdown per task on a given machine)

    Xymon is a GUI tool to analyze the behavior of processes on a given CRC machine. It can be accessed on CRC Xymon. Note that you will need to be on the ND network to see this site.

    Use Xymon to navigate to the specific machine and then view the runtime resource usage of tasks on the machine.

  • qhost command (aggregate summary across all tasks on a given machine)

    You can summarize the resource utilization of all tasks on a given machine using the following qhost command:

qhost -h machine_name

Job Arrays

If you have a large number of job scripts to run, that are largely identical in terms of executable and processing e.g. a parameter sweep where only the input deck changes per run, then you should use a job array to submit your job.

An example job array script is provided below. The SGE batch system will repeatedly submit jobs differentiated by the $SGE_TASK_ID variable which is assigned a value within the task range indicated by the -t SGE task request parameter.:

#!/bin/bash

#$ -pe smp 12          # Specify parallel environment and legal core size
#$ -q long             # Specify queue (use ‘debug’ for development)
#$ -N job_name         # Specify job name
#$ -t 1-10             # Specify number of tasks in array

module load mpich2     # Required modules

mpiexec –n 12 ./foo < data.$SGE_TASK_ID # Application to execute

Warning

To avoid overloading email server, please do not use email notification when submitting an array job.