SHMGET(2) BSD System Calls Manual SHMGET(2)NAMEshmget — get shared memory area identifier
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
int
shmget(key_t key, int size, int shmflg);
DESCRIPTIONshmget() returns the shared memory identifier associated with the key
key.
A shared memory segment is created if either key is equal to IPC_PRIVATE,
or key does not have a shared memory segment identifier associated with
it, and the IPC_CREAT bit is set in shmflg.
If a new shared memory segment is created, the data structure associated
with it (the shmid_ds structure, see shmctl(2)) is initialized as fol‐
lows:
· shm_perm.cuid and shm_perm.uid are set to the effective uid of the
calling process.
· shm_perm.gid and shm_perm.cgid are set to the effective gid of the
calling process.
· shm_perm.mode is set to the lower 9 bits of shmflg.
· shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0
· shm_ctime is set to the current time.
· shm_segsz is set to the value of size.
RETURN VALUES
Upon successful completion a positive shared memory segment identifier is
returned. Otherwise, -1 is returned and the global variable errno is set
to indicate the error.
ERRORS
[EACESS] A shared memory segment is already associated with key
and the caller has no permission to access it.
[EEXIST] Both IPC_CREAT and IPC_EXCL are set in shmflg, and a
shared memory segment is already associated with key.
[ENOSPC] A new shared memory indentifier could not be created
because the system limit for the number of shared mem‐
ory identifiers has been reached.
[ENOENT] IPC_CREAT was not set in shmflg and no shared memory
segment associated with key was found.
[ENOMEM] There is not enough memory left to created a shared
memory segment of the requested size.
SEE ALSOshmctl(2), shmat(2), shmdt(2)BSD August 17, 1995 BSD
