Semaphores

The semaphores are counters which are used to provide synchronization between processes or between threads within a process for shared resources like shared memories.

To see all semaphore settings, run:

# cat /proc/sys/kernel/sem
250     32000   32      128

These values represent SEMMSL, SEMMNS, SEMOPM, and SEMMNI.

Also, you can use the ipcs utility:

# ipcs -ls
------ Semaphore Limits --------
max number of arrays = 128
max semaphores per array = 250
max semaphores system wide = 32000
max ops per semop call = 32
semaphore max value = 32767

To permanently change the values of the four semaphore parameters, add or change the following line in the file:  /etc/sysctl.conf. This file is used during the boot process.

# echo "kernel.sem=250 32000 100 1024" >> /etc/sysctl.conf