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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
sys/shm.h — XSI shared memory facility
SYNOPSIS
#include <sys/shm.h>
DESCRIPTION
The <sys/shm.h> header shall define the following symbolic constants:
SHM_RDONLY Attach read-only (else read-write).
SHM_RND Round attach address to SHMLBA.
SHMLBA Segment low boundary address multiple.
The <sys/shm.h> header shall define the following data types through typedef:
shmatt_t Unsigned integer used for the number of current attaches that must be able to store values at
least as large as a type unsigned short.
The <sys/shm.h> header shall define the shmid_ds structure, which shall include the following members:
struct ipc_perm shm_perm Operation permission structure.
size_t shm_segsz Size of segment in bytes.
pid_t shm_lpid Process ID of last shared memory operation.
pid_t shm_cpid Process ID of creator.
shmatt_t shm_nattch Number of current attaches.
time_t shm_atime Time of last shmat().
time_t shm_dtime Time of last shmdt().
time_t shm_ctime Time of last change by shmctl().
The <sys/shm.h> header shall define the pid_t, size_t, and time_t types as described in <sys/types.h>.
The following shall be declared as functions and may also be defined as macros. Function prototypes shall
be provided.
void *shmat(int, const void *, int);
int shmctl(int, int, struct shmid_ds *);
int shmdt(const void *);
int shmget(key_t, size_t, int);
In addition, the <sys/shm.h> header shall include the <sys/ipc.h> header.
The following sections are informative.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
<sys_ipc.h>, <sys_types.h>
The System Interfaces volume of POSIX.1‐2017, shmat(), shmctl(), shmdt(), shmget()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .