table of contents
other sections
SHMGET(2) | System Calls Manual | SHMGET(2) |
NAME¶
shmget
—
obtain a shared memory identifier
LIBRARY¶
Standard C Library (libc, -lc)SYNOPSIS¶
#include
<sys/types.h>
#include
<sys/ipc.h>
#include
<sys/shm.h>
int
shmget
(key_t
key, size_t
size, int
flag);
DESCRIPTION¶
Based on the values of key and flag,shmget
() returns the identifier of a newly
created or previously existing shared memory segment. The key is analogous to
a filename: it provides a handle that names an IPC object. There are three
ways to specify a key:
- IPC_PRIVATE may be specified, in which case a new IPC object will be created.
- An integer constant may be specified. If no IPC object corresponding to key is specified and the IPC_CREAT bit is set in flag, a new one will be created.
- The ftok(3) may be used to generate a key from a pathname.
S_IRUSR
- Read access for owner.
S_IWUSR
- Write access for owner.
S_IRGRP
- Read access for group.
S_IWGRP
- Write access for group.
S_IROTH
- Read access for other.
S_IWOTH
- Write access for other.
RETURN VALUES¶
Upon successful completion,shmget
() returns
the positive integer identifier of a shared memory segment. Otherwise, -1 is
returned and errno set to indicate the error.
ERRORS¶
Theshmget
() system call will fail if:
- [
EINVAL
] - Size specified is greater than the size of the previously existing segment. Size specified is less than the system imposed minimum, or greater than the system imposed maximum.
- [
ENOENT
] - No shared memory segment was found matching key, and IPC_CREAT was not specified.
- [
ENOSPC
] - The kernel was unable to allocate enough memory to satisfy the request.
- [
EEXIST
] - IPC_CREAT and IPC_EXCL were specified, and a shared memory segment corresponding to key already exists.
SEE ALSO¶
shmat(2), shmctl(2), shmdt(2), stat(2), ftok(3)December 17, 2010 | Debian |