SHMGET

Section: System Calls (2)
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BSD mandoc
NetBSD

NAME

shmget - get shared memory area identifier

SYNOPSIS

Fd #include <sys/types.h> Fd #include <sys/ipc.h> Fd #include <sys/shm.h> Ft int Fn shmget key_t key int size int shmflg

DESCRIPTION

Fn shmget returns the shared memory identifier associated with the key Fa key .

A shared memory segment is created if either Fa key is equal to IPC_PRIVATE, or Fa key does not have a shared memory segment identifier associated with it, and the IPC_CREAT bit is set in Fa 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:

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 Fa 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 Fa 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

Bq Er EACESS: A shared memory segment is already associated with Fa key and the caller has no permission to access it.
Bq Er EEXIST: Both IPC_CREAT and IPC_EXCL are set in Fa shmflg , and a shared memory segment is already associated with Fa key .
Bq Er ENOSPC: A new shared memory indentifier could not be created because the system limit for the number of shared memory identifiers has been reached.
Bq Er ENOENT: IPC_CREAT was not set in Fa shmflg and no shared memory segment associated with Fa key was found.
Bq Er ENOMEM: There is not enough memory left to created a shared memory segment of the requested size.

This document was created by man2html, using the manual pages.
Time: 16:28:59 GMT, April 18, 2022