shmctl(3p) — Linux manual page

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

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

       shmctl — XSI shared memory control operations

SYNOPSIS

       #include <sys/shm.h>

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

DESCRIPTION

       The shmctl() function operates on XSI shared memory (see the Base
       Definitions volume of POSIX.1‐2017, Section 3.346, 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

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

ERRORS

       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

       None.

APPLICATION USAGE

       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

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       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.1‐2017, Section 3.346,
       Shared Memory Object, sys_shm.h(0p)

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 .

IEEE/The Open Group               2017                        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)

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