This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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 Section2.7, XSIInterprocessCommunication can be easily modified to  use  the  alternative
       interfaces.

       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(3POSIX)

       The  shmctl()  function  operates  on XSI shared memory (see the Base Definitions volume of POSIX.1‐2017,
       Section3.346, SharedMemoryObject).  It is unspecified whether this  function  interoperates  with  the
       realtime interprocess communication facilities defined in Section2.8, 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 Section2.7.1, IPCGeneralDescription.

                   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.

       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
              Section2.7, XSIInterprocessCommunication.

       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.

       Thefollowingsectionsareinformative.

       None.

       None.

       shmctl — XSI shared memory control operations

       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.

       None.

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

Section2.7,  XSIInterprocessCommunication,  Section2.8,  Realtime,  shmat(),  shmdt(),  shmget(),
       shm_open(), shm_unlink()

       The Base Definitions volume of POSIX.1‐2017, Section3.346, SharedMemoryObject, <sys_shm.h>

       #include <sys/shm.h>

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