1SHMCTL(3P)                 POSIX Programmer's Manual                SHMCTL(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       shmctl - XSI shared memory control operations
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SYNOPSIS

15       #include <sys/shm.h>
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17       int shmctl(int shmid, int cmd, struct shmid_ds *buf);
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DESCRIPTION

21       The shmctl() function operates on XSI shared memory (see the Base Defi‐
22       nitions  volume  of  IEEE Std 1003.1-2001, Section 3.340, Shared Memory
23       Object). It is unspecified whether this function interoperates with the
24       realtime interprocess communication facilities defined in Realtime .
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26       The shmctl() function provides a variety of shared memory control oper‐
27       ations as specified by cmd. The following values for cmd are available:
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29       IPC_STAT
30              Place the current value of each  member  of  the  shmid_ds  data
31              structure associated with shmid into the structure pointed to by
32              buf. The contents of the structure are defined in <sys/shm.h>.
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34       IPC_SET
35              Set the value of the following  members  of  the  shmid_ds  data
36              structure associated with shmid to the corresponding value found
37              in the structure pointed to by buf:
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40              shm_perm.uid
41              shm_perm.gid
42              shm_perm.mode    Low-order nine bits.
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44       IPC_SET can only be executed by a process that has an effective user ID
45       equal to either that of a process with appropriate privileges or to the
46       value of shm_perm.cuid or shm_perm.uid in the shmid_ds  data  structure
47       associated with shmid.
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49       IPC_RMID
50              Remove  the shared memory identifier specified by shmid from the
51              system and destroy the shared memory segment and  shmid_ds  data
52              structure associated with it. IPC_RMID can only be executed by a
53              process that has an effective user ID equal to either that of  a
54              process   with   appropriate  privileges  or  to  the  value  of
55              shm_perm.cuid or shm_perm.uid in  the  shmid_ds  data  structure
56              associated with shmid.
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RETURN VALUE

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

64       The shmctl() function shall fail if:
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66       EACCES The argument cmd is equal to IPC_STAT and  the  calling  process
67              does  not  have read permission; see XSI Interprocess Communica‐
68              tion .
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70       EINVAL The value of shmid is not a valid shared memory  identifier,  or
71              the value of cmd is not a valid command.
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73       EPERM  The  argument cmd is equal to IPC_RMID or IPC_SET and the effec‐
74              tive user ID of the calling process is not equal to  that  of  a
75              process  with  appropriate privileges and it is not equal to the
76              value of shm_perm.cuid or shm_perm.uid  in  the  data  structure
77              associated with shmid.
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80       The shmctl() function may fail if:
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82       EOVERFLOW
83              The  cmd  argument  is  IPC_STAT and the gid or uid value is too
84              large to be stored in the structure pointed to by the buf  argu‐
85              ment.
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88       The following sections are informative.
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EXAMPLES

91       None.
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APPLICATION USAGE

94       The  POSIX Realtime Extension defines alternative interfaces for inter‐
95       process communication. Application  developers  who  need  to  use  IPC
96       should design their applications so that modules using the IPC routines
97       described in XSI Interprocess Communication can be easily  modified  to
98       use the alternative interfaces.
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RATIONALE

101       None.
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FUTURE DIRECTIONS

104       None.
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SEE ALSO

107       XSI  Interprocess  Communication, Realtime, shmat(), shmdt(), shmget(),
108       shm_open(),   shm_unlink(),   the   Base    Definitions    volume    of
109       IEEE Std 1003.1-2001, <sys/shm.h>
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112       Portions  of  this text are reprinted and reproduced in electronic form
113       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
114       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
115       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
116       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
117       event of any discrepancy between this version and the original IEEE and
118       The  Open Group Standard, the original IEEE and The Open Group Standard
119       is the referee document. The original Standard can be  obtained  online
120       at http://www.opengroup.org/unix/online.html .
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124IEEE/The Open Group                  2003                           SHMCTL(3P)
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