Where is a named semaphore stored?

Question

A named semaphore (using semaphore.h) is identified by a name in the form /somename; that is, a null-terminated string of up to NAME_MAX-4 (i.e., 251) characters consisting of an initial slash, followed by one or more characters, none of which are slashes.

As the name corresponds to pathname in filesystem. Where is this semaphore located?ipcs is for System V semaphores.How to locate POSIX semaphores?

Solution 1

From man 7 sem_overview :

Accessing named semaphores via the filesystem

On Linux, named semaphores are created in a virtual filesystem, normally mounted under /dev/shm, with names of the form sem.somename. (This is the reason that semaphore names are limited to NAME_MAX-4 rather than NAME_MAX characters.)

Solution 2

/proc/<pid>/maps/ will show you the memory mapping of a process with a specific PID. (Related question: https://stackoverflow.com/questions/1401359/understanding-linux-proc-id-maps)

From the output, POSIX semaphores are shown as files in /dev/shm/.

Comments

[Admin]

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[Manu Kanthan]

This answer is a verbatim copy from man 7 sem_overview: man7.org/linux/man-pages/man7/sem_overview.7.html and should be annotated as such.