Choosing an HTCondor Universe¶
A universe in HTCondor defines an execution environment for a job. HTCondor supports several different universes:
The universe under which a job runs is specified in the submit description file. If a universe is not specified, the default is vanilla.
The vanilla universe is a good default, for it has the fewest restrictions on the job. The grid universe allows users to submit jobs using HTCondor’s interface. These jobs are submitted for execution on grid resources. The java universe allows users to run jobs written for the Java Virtual Machine (JVM). The scheduler universe allows users to submit lightweight jobs to be spawned by the program known as a daemon on the submit host itself. The parallel universe is for programs that require multiple machines for one job. See the Parallel Applications (Including MPI Applications) section for more about the Parallel universe. The vm universe allows users to run jobs where the job is no longer a simple executable, but a disk image, facilitating the execution of a virtual machine. Container universe allows the user to specify a container image for one of many possible container runtimes, just as singularity or docker, and condor will run the job in the appropriate container runtimes. The docker universe runs a Docker container as an HTCondor job.
The vanilla universe in HTCondor is intended for most programs. Shell scripts are another case where the vanilla universe is useful.
Access to the job’s input and output files is a concern for vanilla universe jobs. One option is for HTCondor to rely on a shared file system, such as NFS or AFS. Alternatively, HTCondor has a mechanism for transferring files on behalf of the user. In this case, HTCondor will transfer any files needed by a job to the execution site, run the job, and transfer the output back to the submitting machine.
The Grid universe in HTCondor is intended to provide the standard HTCondor interface to users who wish to start jobs intended for remote management systems. The Grid Universe section has details on using the Grid universe. The manual page for condor_submit has detailed descriptions of the grid-related attributes.
A program submitted to the Java universe may run on any sort of machine with a JVM regardless of its location, owner, or JVM version. HTCondor will take care of all the details such as finding the JVM binary and setting the classpath.
The scheduler universe allows users to submit lightweight jobs to be run immediately, alongside the condor_schedd daemon on the submit host itself. Scheduler universe jobs are not matched with a remote machine, and will never be preempted. The job’s requirements expression is evaluated against the condor_schedd ‘s ClassAd.
Originally intended for meta-schedulers such as condor_dagman, the scheduler universe can also be used to manage jobs of any sort that must run on the submit host.
However, unlike the local universe, the scheduler universe does not use a condor_starter daemon to manage the job, and thus offers limited features and policy support. The local universe is a better choice for most jobs which must run on the submit host, as it offers a richer set of job management features, and is more consistent with other universes such as the vanilla universe. The scheduler universe may be retired in the future, in favor of the newer local universe.
The local universe allows an HTCondor job to be submitted and executed with different assumptions for the execution conditions of the job. The job does not wait to be matched with a machine. It instead executes right away, on the machine where the job is submitted. The job will never be preempted. The job’s requirements expression is evaluated against the condor_schedd ‘s ClassAd.
The parallel universe allows parallel programs, such as MPI jobs, to be run within the opportunistic HTCondor environment. Please see the Parallel Applications (Including MPI Applications) section for more details.
HTCondor facilitates the execution of KVM and Xen virtual machines with the vm universe.
Please see the Virtual Machine Applications section for details.
The docker universe runs a docker container on an execute host as a job. Please see the Docker Universe Applications section for details.