Grid Services

ARC tools

The tools required for grid job submission and management are available from CVMFS:

export ATLAS_LOCAL_ROOT_BASE=/cvmfs/atlas.cern.ch/repo/ATLASLocalRootBase
alias setupATLAS='source ${ATLAS_LOCAL_ROOT_BASE}/user/atlasLocalSetup.sh'
setupATLAS

Certificates and proxies

To use grid resources, you will need a certificate, from which you can generate a proxy certificate. The proxy certificate has a relatively short lifetime, and is used to actually submit the job. A proxy is associated with a particular Virtual Organisation (VO), for example vo.scotgrid.ac.uk, which is selected when it is created. You can generate a proxy using the arcproxy command:

For example, to generate a proxy for the vo.scotgrid.ac.uk VO:

Job description (xRSL)

Before submitting a job, you need to create a file which describes the features of the job for ARC (its executable, the names of input and output files, what to do with logs, etc.). This file is written in the Extended Resource Specification Language (xRSL). A simple job description which runs a script called test.sh could look like this:

Submitting a job

Jobs are submitted using the arcsub command:

For example, to submit test.xrsl to svr011 at Glasgow:

When a job is submitted successfully, you will be presented with its job ID which can be used to refer to the job later. Information about submitted jobs is also recorded in a job list file; by default, this file is ~/.arc/jobs.dat (~/.arc/jobs.xml with some earlier versions of ARC), but you can choose a different location by supplying the -j argument to arcsub:

For example:

Querying the status of a job

You can obtain information about the status of jobs using the arcstat command:

For example, to obtain information about the job submitted in the previous step:

You can also query the status of all jobs in a job list file:

Retrieving job output

Output and log files for a job can be retrieved using the arcget command. As when querying the status of a job, you can use either a job ID or a job list file with this command:

For example, to get the output of the job submitted above:

Copying input and output files ("staging")

You can tell ARC to copy input and output files to and from the compute element by including additional attributes in your xRSL file:

Files used in the exectuable, stdout and stderr attributes are transferred automatically, but other files should be listed in the inputFiles or outputFiles attribute as necessary. The inputFiles and outputFiles attributes each take one or more values like this:

Where <URL> is left blank, ARC transfers the file to or from the submission machine (this would be the case for input.dat, output.txt and results.tgz in the example xRSL above). Alternatively, a URL may be provided to copy the file to or from a remote resource: