# 10. Session directory

PRRTE establishes a “session directory” on the filesystem to serve as a top-level location for temporary files used by both the local PRRTE daemon and its child processes.

This is done to enable quick and easy cleanup in the event that PRRTE is unable to fully cleanup after itself.

More detail on session directories is provided in the How Things Work session directory section.

## 10.1. Directory location

PRRTE decides where to located the root of the session directory by examining the following (in precedence order):

1. If the value of the `prte_top_session_dir` MCA parameter is not empty, use that (it defaults to empty).

   Note

   MCA parameters can be set via environment variables, on the command line, or in a parameter file.

   Note

   If necessary, the value of the top session directory on the local node where the launcher (e.g., `prun`, `prterun`, or `mpirun`) is executing can be set separately from the value to be used on compute nodes via the `prte_local_tmpdir_base` and `prte_remote_tmpdir_base` parameters.

2. If the environment variable `TMPDIR` is not empty, use that.

3. If the environment variable `TEMP` is not empty, use that.

4. If the environment variable `TMP` is not empty, use that.

5. Use `/tmp`

## 10.2. Directory name

By default, the session directory name is set to

    <tool>.<nodename>.<pid>.<uid>

where tool is the argv[0] of the process setting up the session directory. In most cases, this will be either prte, prterun, or prted - though special tools such as psched may also create a session directory tree.

The session directory name includes the PID of the daemon process to allow a user to have multiple instances of a tool concurrently executing on a node.

Note

Each tool will generate its own session directory tree. This is done to avoid cleanup race conditions where one tool might cleanup the session directory, and thereby remove the contact information for a tool that is continuing to execute.

## 10.3. Tools

In the case of tools, the rendezvous files containing connection information for a target server are located in the session directory tree. Thus, it may be necessary to point the tool at the location where those files can be found if that location is other than the expected default.