sys_shm.h - Man Page

XSI shared memory facility


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.


#include <sys/shm.h>


The <sys/shm.h> header shall define the following symbolic constants:


Attach read-only (else read-write).


Round attach address to SHMLBA.


Segment low boundary address multiple.

The <sys/shm.h> header shall define the following data types through typedef:


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




Future Directions


See Also

<sys_ipc.h>, <sys_types.h>

The System Interfaces volume of POSIX.1-2017, shmat(), shmctl(), shmdt(), shmget()

Referenced By

shmat(3p), shmctl(3p), shmdt(3p), shmget(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual