plucky (2) shmctl.2freebsd.gz

NAME

     shmctl — shared memory control

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     int
     shmctl(int shmid, int cmd, struct shmid_ds *buf);

DESCRIPTION

     Performs the action specified by cmd on the shared memory segment identified by shmid:

     IPC_STAT     Fetch the segment's struct shmid_ds, storing it in the memory pointed to by buf.

     IPC_SET      Changes the shm_perm.uid, shm_perm.gid, and shm_perm.mode members of the segment's struct
                  shmid_ds to match those of the struct pointed to by buf.  The calling process's effective uid
                  must match either shm_perm.uid or shm_perm.cuid, or it must have superuser privileges.

     IPC_RMID     Removes the segment from the system.  The removal will not take effect until all processes
                  having attached the segment have exited.  For the operation to succeed, the calling process's
                  effective uid must match shm_perm.uid or shm_perm.cuid, or the process must have superuser
                  privileges.  If the kern.ipc.shm_allow_removed sysctl(3) variable is set to 0, once the
                  IPC_RMID operation has taken place, no further processes will be allowed to attach the
                  segment.

     The shmid_ds structure is defined as follows:

     struct shmid_ds {
         struct ipc_perm shm_perm;   /* operation permission structure */
         size_t          shm_segsz;  /* size of segment in bytes */
         pid_t           shm_lpid;   /* process ID of last shared memory op */
         pid_t           shm_cpid;   /* process ID of creator */
         int             shm_nattch; /* number of current attaches */
         time_t          shm_atime;  /* time of last shmat() */
         time_t          shm_dtime;  /* time of last shmdt() */
         time_t          shm_ctime;  /* time of last change by shmctl() */
     };

RETURN VALUES

     The shmctl() function returns the value 0 if successful; otherwise the value -1 is returned and the global
     variable errno is set to indicate the error.

ERRORS

     The shmctl() system call will fail if:

     [EINVAL]           Invalid operation, or no shared memory segment was found corresponding to shmid.

     [EPERM]            The calling process's effective uid does not match the uid of the shared memory
                        segment's owner or creator.

     [EACCES]           Permission denied due to mismatch between operation and mode of shared memory segment.

SEE ALSO

     shmat(2), shmdt(2), shmget(2), ftok(3)