System V Semaphore Arrays in Debian 6.x/Knoppix 6.x

A semaphore array is a System V IPC object that allows processes to synchronize access to shared resources. Any process can create a semaphore array, modify it and leave it for other processes to modify later on. Any process can immediately remove a semaphore array regardless of whether another process is using it. Semaphore arrays exist until they are removed or system shutdown.

The data strucuture of the semaphore array object is:

struct semid_ds

{

  struct ipc_perm sem_perm;
  time_t sem_otime;          /* last operation time  */

  time_t sem_ctime;          /* last change time */

  unsigned long sem_nsems;   /* count of sems in set */

};

Both commands list all the semaphore array objects in use on the system:

cat /proc/sysvipc/sem;

ipcs -s; ipcs -s -t; ipcs -s -p; ipcs -s -c; ipcs -s -l; ipcs -s -u;

Create semaphore array objects on the system:

ipcmk -S <number of elements> -p <permission bits>;

Remove semaphore array objects from the system:

ipcrm -S <semaphore key>;

ipcrm -s <semaphore id>;

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