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shmget(2) [freebsd man page]

SHMGET(2)						      BSD System Calls Manual							 SHMGET(2)

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: o IPC_PRIVATE may be specified, in which case a new IPC object will be created. o 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. o The ftok(3) may be used to generate a key from a pathname. The mode of a newly created IPC object is determined by OR'ing the following constants into the flag argument: 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. When creating a new shared memory segment, size indicates the desired size of the new segment in bytes. The size of the segment may be rounded up to a multiple convenient to the kernel (i.e., the page size). 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
The shmget() 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) BSD
December 17, 2010 BSD

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SHMGET(2)						      BSD System Calls Manual							 SHMGET(2)

shmget -- 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); DESCRIPTION
shmget() 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 follows: o shm_perm.cuid and shm_perm.uid are set to the effective uid of the calling process. o shm_perm.gid and shm_perm.cgid are set to the effective gid of the calling process. o shm_perm.mode is set to the lower 9 bits of shmflg. o shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0 o shm_ctime is set to the current time. o 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 memory 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 ALSO
shmctl(2), shmat(2), shmdt(2) BSD
August 17, 1995 BSD

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