PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

SHMCTL(3P)                POSIX Programmer's Manual               SHMCTL(3P)

PROLOG         top

       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         top

       shmctl — XSI shared memory control operations

SYNOPSIS         top

       #include <sys/shm.h>

       int shmctl(int shmid, int cmd, struct shmid_ds *buf);

DESCRIPTION         top

       The shmctl() function operates on XSI shared memory (see the Base
       Definitions volume of POSIX.1‐2008, Section 3.342, Shared Memory
       Object).  It is unspecified whether this function interoperates with
       the realtime interprocess communication facilities defined in Section
       2.8, Realtime.

       The shmctl() function provides a variety of shared memory control
       operations as specified by cmd.  The following values for cmd are
       available:

       IPC_STAT    Place the current value of each member of the shmid_ds
                   data structure associated with shmid into the structure
                   pointed to by buf.  The contents of the structure are
                   defined in <sys/shm.h>.

       IPC_SET     Set the value of the following members of the shmid_ds
                   data structure associated with shmid to the corresponding
                   value found in the structure pointed to by buf:

                       shm_perm.uid
                       shm_perm.gid
                       shm_perm.mode    Low-order nine bits.

                   Also, the shm_ctime timestamp shall be set to the current
                   time, as described in Section 2.7.1, IPC General
                   Description.

                   IPC_SET can only be executed by a process that has an
                   effective user ID equal to either that of a process with
                   appropriate privileges or to the value of shm_perm.cuid
                   or shm_perm.uid in the shmid_ds data structure associated
                   with shmid.

       IPC_RMID    Remove the shared memory identifier specified by shmid
                   from the system and destroy the shared memory segment and
                   shmid_ds data structure associated with it. IPC_RMID can
                   only be executed by a process that has an effective user
                   ID equal to either that of a process with appropriate
                   privileges or to the value of shm_perm.cuid or
                   shm_perm.uid in the shmid_ds data structure associated
                   with shmid.

RETURN VALUE         top

       Upon successful completion, shmctl() shall return 0; otherwise, it
       shall return −1 and set errno to indicate the error.

ERRORS         top

       The shmctl() function shall fail if:

       EACCES The argument cmd is equal to IPC_STAT and the calling process
              does not have read permission; see Section 2.7, XSI
              Interprocess Communication.

       EINVAL The value of shmid is not a valid shared memory identifier, or
              the value of cmd is not a valid command.

       EPERM  The argument cmd is equal to IPC_RMID or IPC_SET and the
              effective user ID of the calling process is not equal to that
              of a process with appropriate privileges and it is not equal
              to the value of shm_perm.cuid or shm_perm.uid in the data
              structure associated with shmid.

       The shmctl() function may fail if:

       EOVERFLOW
              The cmd argument is IPC_STAT and the gid or uid value is too
              large to be stored in the structure pointed to by the buf
              argument.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       The POSIX Realtime Extension defines alternative interfaces for
       interprocess communication. Application developers who need to use
       IPC should design their applications so that modules using the IPC
       routines described in Section 2.7, XSI Interprocess Communication can
       be easily modified to use the alternative interfaces.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.7, XSI Interprocess Communication, Section 2.8, Realtime,
       shmat(3p), shmdt(3p), shmget(3p), shm_open(3p), shm_unlink(3p)

       The Base Definitions volume of POSIX.1‐2008, Section 3.342, Shared
       Memory Object, sys_shm.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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 .

IEEE/The Open Group                 2013                          SHMCTL(3P)

Pages that refer to this page: sys_shm.h(0p)ipcrm(1p)shmat(3p)shmdt(3p)shmget(3p)shm_open(3p)shm_unlink(3p)