SHMGET(2) INTERACTIVE UNIX System SHMGET(2)
NAME
shmget - get shared memory segment identifier
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
int shmget (key, size, shmflg)
key_t key;
int size, shmflg;
DESCRIPTION
The shmget system call returns the shared memory identifier
associated with key.
A shared memory identifier and associated data structure and
shared memory segment of at least size bytes [see intro(2)]
are created for key if one of the following is true:
Key is equal to IPC_PRIVATE.
Key does not already have a shared memory identifier
associated with it, and (shmflg & IPC_CREAT) is
``true''.
Upon creation, the data structure associated with the new
shared memory identifier is initialized as follows:
Shm_perm.cuid, shm_perm.uid, shm_perm.cgid, and
shm_perm.gid are set equal to the effective user ID and
effective group ID, respectively, of the calling pro-
cess.
The low-order 9 bits of shm_perm.mode are set equal to
the low-order 9 bits of shmflg. Shm_segsz is set equal
to the value of size.
Shm_lpid, shm_nattch, shm_atime, and shm_dtime are set
equal to 0.
Shm_ctime is set equal to the current time.
The shmget system call will fail if one or more of the fol-
lowing is true:
[EINVAL] Size is less than the system-imposed minimum
or greater than the system-imposed maximum.
[EACCES] A shared memory identifier exists for key,
but operation permission [see intro(2)] as
specified by the low-order 9 bits of shmflg
would not be granted.
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SHMGET(2) INTERACTIVE UNIX System SHMGET(2)
[EINVAL] A shared memory identifier exists for key,
but the size of the segment associated with
it is less than size, and size is not equal
to zero.
[ENOENT] A shared memory identifier does not exist for
key, and (shmflg & IPC_CREAT) is ``false''.
[ENOSPC] A shared memory identifier is to be created,
but the system-imposed limit on the maximum
number of allowed shared memory identifiers
system wide would be exceeded.
[ENOMEM] A shared memory identifier and associated
shared memory segment are to be created, but
the amount of available memory is not suffi-
cient to fill the request.
[EEXIST] A shared memory identifier exists for key but
[(shmflg & IPC_CREAT) and (shmflg& IPC_EXCL)]
are ``true''.
SEE ALSO
intro(2), shmctl(2), shmop(2).
DIAGNOSTICS
Upon successful completion, a non-negative integer, namely a
shared memory identifier is returned. Otherwise, a value of
-1 is returned, and errno is set to indicate the error.
NOTES
The user must explicitly remove shared memory segments after
the last reference to them has been removed.
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