"/dev/shm" is a temporary filesystem in Linux and Unix-like operating systems. It stands for "shared memory." It is a special directory that behaves like memory, but it's actually stored on disk. It's typically mounted as a RAM-based filesystem, meaning it resides in memory (RAM).
It's often used for temporary file storage by programs that require fast access to temporary files. Files created in /dev/shm are stored in memory, which can result in faster access compared to traditional disk-based storage.

The permissions required for such a directory are explained below.

Linux

The default permissions given to the "/dev/shm" directory is 777. This means that all users can freely access the shared memory space.
This also ensures that TIBCO Data Virtualization, irrespective of which user is logged in, can use this space without any restrictions.

Any permission changes made to the "/dev/shm" directory, will result in service startup failure, especially the repo service.
An error like below can be seen in such a scenario:

waiting for server to start....2024-05-24 16:03:50.910 UTC [ 8011]FATAL: could not open shared memory segment "/PostgreSQL.1134400060": Permission denied
2024-05-24 16:03:50.918 UTC [ 8011]LOG: database system is shut down

This is because TDV, more specifically, the Postgres which acts as TDV's metadata repository, is very particular about the permission level required for individual service/component.
In this case, the PostgreSQL.<PID of Postgres> binary file is created by the Postgres Server to store metadata under the directory "/dev/shm". Hence it should be accessible to TDV at all times.

This article will explain the significance of the directory "/dev/shm" and what are the default as well as appropriate permissions for that directory.