When your jobs run, any output that gets generated is specifically written to the execute node on which the job ran. In order to get access to your output files, a copy of the output must be transferred back to your OSG Connect login node.

This guide will describe the necessary steps, along with important considerations, for transferring your output files back to your /home directory on your OSG Connect login node.

Important Considerations

As described in the Introduction to Data Management on OSG Connect, any output <1GB should be staged in your /home directory. For output files >1GB, please refer to our Transfer Large Input and Output Files >1GB In Size guide.

If your jobs use any input files >1GB that are transferred from your /public directory using StacheCash, it is important that these files get deleted from the job's working directory or moved to a subdirectory so that HTCondor will not transfer these large files back to your /home directory.

Use HTCondor To Transfer Output <1GB

By default, HTCondor will transfer any new or modified files in the job's top-level directory back to your /home directory location from which the condor_submit command was performed. This behavior only applies to files in the top-level directory of where your job executes, meaning HTCondor will ignore any files created in subdirectories of the job's top-level directory. Several options exist for modifying this default output file transfer behavior, including those described in this guide. To learn more, please contact us at support@osg-htc.org.

What is the top-level directory of a job?

Before executing a job, HTCondor will create a new directory on the execute node just for your job - this is the top-level directory of the job and the path is stored in the environment variable _CONDOR_SCRATCH_DIR. All of the input files transferred via transfer_input_files will first be written to this directory and it is from this path that a job starts to execute. After a job has completed the top-level directory and all of it's contents are deleted.

What if my output file(s) are not written to the top-level directory?

If your output files are written to a subdirectory, use the steps described below to convert the output directory to a "tarball" that is written to the top-level directory.

Alternatively, you can include steps in the executable bash script of your job to move (i.e. mv) output files from a subdirectory to the top-level directory. For example, if there is an output file that needs to be transferred back to the login node named job_output.txt written to job_output/:

#! /bin/bash

# various commands needed to run your job

# move csv files to scratch dir
mv job_output/job_output.txt $_CONDOR_SCRATCH_DIR

Group Multiple Output Files For Convenience

If your jobs will generate multiple output files, we recommend combining all output into a compressed tar archive for convenience, particularly when transferring your results to your local computer from your login node. To create a compressed tar archive, include commands in your your bash executable script to create a new subdirectory, move all of the output to this new subdirectory, and create a tar archive. For example:

#! /bin/bash

# various commands needed to run your job

# create output tar archive
mkidr my_output
mv my_job_output.csv my_job_output.svg my_output/
tar -czf my_job.output.tar.gz my_ouput/

The example above will create a file called my_job.output.tar.gz that contains all the output that was moved to my_output. Be sure to create my_job.output.tar.gz in the top-level directory of where your job executes and HTCondor will automatically transfer this tar archive back to your /home directory.

Select Specific Output Files To Transfer to /home Using HTCondor

As described above, HTCondor will, by default, transfer any files that are generated during the execution of your job(s) back to your /home directory. If your job(s) will produce multiple output files but you only need to retain a subset of these output files, we recommend deleting the unrequired output files or moving them to a subdirectory as a step in the bash executable script of your job - only the output files that remain in the top-level directory will be transferred back to your /home directory.

In cases where a bash script is not used as the excutable of your job and you wish to have only specific output files transferred back, please contact us at support@osg-htc.org.

Get Additional Options For Managing Job Output

Several options exist for managing output file transfers back to your /home directory and we encourage you to get in touch with us at support@osg-htc.org to help identify the best solution for your needs.


This page was updated on Sep 15, 2022 at 15:40 from start/data/output-file-transfer-via-htcondor.md.