2 .\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
4 .\" All rights reserved.
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31 .Nd obtain a shared memory identifier
37 .Fn shmget "key_t key" "size_t size" "int flag"
39 Based on the values of
44 returns the identifier of a newly created or previously existing shared
47 .\" The following bit about keys and modes also applies to semaphores
48 .\" and message queues.
51 is analogous to a filename: it provides a handle that names an
53 There are three ways to specify a key:
56 IPC_PRIVATE may be specified, in which case a new IPC object
59 An integer constant may be specified.
60 If no IPC object corresponding
63 is specified and the IPC_CREAT bit is set in
65 a new one will be created.
69 may be used to generate a key from a pathname.
72 The mode of a newly created IPC object is determined by
73 which are set by ORing these constants into the
78 Read access for owner.
80 Write access for owner.
82 Read access for group.
84 Write access for group.
86 Read access for other.
88 Write access for other.
91 .\" XXX - we should also mention how uid, euid, and gid affect ownership
94 .\" end section about keys and modes
97 When creating a new shared memory segment,
99 indicates the desired size of the new segment in bytes.
101 of the segment may be rounded up to a multiple convenient to the
102 kernel (i.e., the page size).
104 Upon successful completion,
106 returns the positive integer identifier of a shared memory segment.
107 Otherwise, -1 is returned and
109 set to indicate the error.
117 .\" XXX What about ipcperm failing?
120 Size specified is greater than the size of the previously existing segment.
121 Size specified is less than the system imposed minimum, or greater than
122 the system imposed maximum.
124 No shared memory segment was found matching
126 and IPC_CREAT was not specified.
128 The kernel was unable to allocate enough memory to
131 IPC_CREAT and IPC_EXCL were specified, and a shared memory segment