1SHMCTL(3P) POSIX Programmer's Manual SHMCTL(3P)
2
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.
10
12 shmctl — XSI shared memory control operations
13
15 #include <sys/shm.h>
16 int shmctl(int shmid, int cmd, struct shmid_ds *buf);
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20 The shmctl() function operates on XSI shared memory (see the Base Defi‐
21 nitions volume of POSIX.1‐2017, Section 3.346, Shared Memory Object).
22 It is unspecified whether this function interoperates with the realtime
23 interprocess communication facilities defined in Section 2.8, Realtime.
24 The shmctl() function provides a variety of shared memory control oper‐
26 ations as specified by cmd. The following values for cmd are avail‐
27 able:
28 IPC_STAT Place the current value of each member of the shmid_ds data
30 structure associated with shmid into the structure pointed
31 to by buf. The contents of the structure are defined in
32 <sys/shm.h>.
33 IPC_SET Set the value of the following members of the shmid_ds data
35 structure associated with shmid to the corresponding value
36 found in the structure pointed to by buf:
37 shm_perm.uid
40 shm_perm.gid
41 shm_perm.mode Low-order nine bits.
42 Also, the shm_ctime timestamp shall be set to the current
44 time, as described in Section 2.7.1, IPC General Descrip‐
45 tion.
46 IPC_SET can only be executed by a process that has an
48 effective user ID equal to either that of a process with
49 appropriate privileges or to the value of shm_perm.cuid or
50 shm_perm.uid in the shmid_ds data structure associated with
51 shmid.
52 IPC_RMID Remove the shared memory identifier specified by shmid from
54 the system and destroy the shared memory segment and
55 shmid_ds data structure associated with it. IPC_RMID can
56 only be executed by a process that has an effective user ID
57 equal to either that of a process with appropriate privi‐
58 leges or to the value of shm_perm.cuid or shm_perm.uid in
59 the shmid_ds data structure associated with shmid.
60
62 Upon successful completion, shmctl() shall return 0; otherwise, it
63 shall return -1 and set errno to indicate the error.
64
66 The shmctl() function shall fail if:
67 EACCES The argument cmd is equal to IPC_STAT and the calling process
69 does not have read permission; see Section 2.7, XSI Interprocess
70 Communication.
71 EINVAL The value of shmid is not a valid shared memory identifier, or
73 the value of cmd is not a valid command.
74 EPERM The argument cmd is equal to IPC_RMID or IPC_SET and the effec‐
76 tive user ID of the calling process is not equal to that of a
77 process with appropriate privileges and it is not equal to the
78 value of shm_perm.cuid or shm_perm.uid in the data structure
79 associated with shmid.
80 The shmctl() function may fail if:
82 EOVERFLOW
84 The cmd argument is IPC_STAT and the gid or uid value is too
85 large to be stored in the structure pointed to by the buf argu‐
86 ment.
87 The following sections are informative.
89
91 None.
92
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 Section 2.7, XSI Interprocess Communication can be easily
98 modified to use the alternative interfaces.
99
101 None.
102
104 None.
105
107 Section 2.7, XSI Interprocess Communication, Section 2.8, Realtime,
108 shmat(), shmdt(), shmget(), shm_open(), shm_unlink()
109 The Base Definitions volume of POSIX.1‐2017, Section 3.346, Shared Mem‐
111 ory Object, <sys_shm.h>
112
114 Portions of this text are reprinted and reproduced in electronic form
115 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
116 table Operating System Interface (POSIX), The Open Group Base Specifi‐
117 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
118 Electrical and Electronics Engineers, Inc and The Open Group. In the
119 event of any discrepancy between this version and the original IEEE and
120 The Open Group Standard, the original IEEE and The Open Group Standard
121 is the referee document. The original Standard can be obtained online
122 at http://www.opengroup.org/unix/online.html .
123 Any typographical or formatting errors that appear in this page are
125 most likely to have been introduced during the conversion of the source
126 files to man page format. To report such errors, see https://www.ker‐
127 nel.org/doc/man-pages/reporting_bugs.html .
128IEEE/The Open Group 2017 SHMCTL(3P)