SHMGET(S) XENIX System V SHMGET(S)
Name
shmget - Gets a shared memory segment.
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
int shmget (key, size, shmflg)
key_t key;
int size, shmflg;
Description
shmget returns the shared memory identifier associated with
key.
A shared memory identifier and an associated data structure
and shared memory segment of size size bytes (see intro(S))
are created for key if one of the following are 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
process.
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.
shmget will fail if one or more of the following are true:
size is less than the system-imposed minimum or greater
than the system-imposed maximum. The minimum for 286
processes is 1 byte, and the maximum is 64K or 65535
bytes. The minimum and maximum for 386 processes are
configurable. [EINVAL]
A shared memory identifier exists for key but operation
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SHMGET(S) XENIX System V SHMGET(S)
permission (see intro(S)) as specified by the low-order
9 bits of shmflg would not be granted. [EACCES]
A shared memory identifier exists for key but the size
of the segment associated with it is less than size,
which cannot be equal to zero. [EINVAL]
A shared memory identifier does not exist for key and
(shmflg & IPC_CREAT) is ``false''. [ENOENT]
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. [ENOSPC]
A shared memory identifier and associated shared memory
segment are to be created but the amount of available
physical memory is not sufficient to fill the request.
[ENOMEM]
A shared memory identifier exists for key but ( (shmflg
& IPC_CREAT) and (shmflg & IPC_EXCL) ) is ``true''. -
[EEXIST]
Return Value
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.
See Also
intro(S), shmctl(S), shmop(S)
Notes
Programs using this function must be compiled with -Me
compiler option.
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