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shmctl(3p) — Linux manual page

SHMCTL(3P)              POSIX Programmer's ManualSHMCTL(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(intshmid, intcmd, struct shmid_ds *buf);

DESCRIPTION        top

       Theshmctl() function operates on XSI shared memory (see the Base       Definitions volume of POSIX.1‐2017,Section 3.346,Shared MemoryObject).  It is unspecified whether this function interoperates       with the realtime interprocess communication facilities defined inSection 2.8,Realtime.       Theshmctl() function provides a variety of shared memory control       operations as specified bycmd.  The following values forcmd are       available:       IPC_STAT    Place the current value of each member of theshmid_ds                   data structure associated withshmid into the                   structure pointed to bybuf.  The contents of the                   structure are defined in<sys/shm.h>.       IPC_SET     Set the value of the following members of theshmid_ds                   data structure associated withshmid to the                   corresponding value found in the structure pointed to                   bybuf:                       shm_perm.uid                       shm_perm.gid                       shm_perm.mode    Low-order nine bits.                   Also, theshm_ctime timestamp shall be set to the                   current time, as described inSection 2.7.1,IPCGeneral 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 ofshm_perm.cuid orshm_perm.uid in theshmid_dsdata                   structure associated withshmid.       IPC_RMID    Remove the shared memory identifier specified byshmid                   from the system and destroy the shared memory segment                   andshmid_dsdata 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 ofshm_perm.cuid orshm_perm.uid in theshmid_dsdata                   structure associated withshmid.

RETURN VALUE        top

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

ERRORS        top

       Theshmctl() function shall fail if:EACCESThe argumentcmd is equal to IPC_STAT and the calling              process does not have read permission; seeSection 2.7,XSIInterprocess Communication.EINVALThe value ofshmid is not a valid shared memory identifier,              or the value ofcmd is not a valid command.EPERMThe argumentcmd 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 ofshm_perm.cuid orshm_perm.uid in the              data structure associated withshmid.       Theshmctl() function may fail if:EOVERFLOW              Thecmd argument is IPC_STAT and thegid oruid value is              too large to be stored in the structure pointed to by thebuf 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 inSection 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.1‐2017,Section 3.346,SharedMemory Object,sys_shm.h(0p)

COPYRIGHT        top

       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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017SHMCTL(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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