2 .\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
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33 .Nd obtain a shared memory identifier
39 .Fn shmget "key_t key" "size_t size" "int flag"
41 Based on the values of
46 returns the identifier of a newly created or previously existing shared
49 .\" The following bit about keys and modes also applies to semaphores
50 .\" and message queues.
53 is analogous to a filename: it provides a handle that names an
55 There are three ways to specify a key:
58 IPC_PRIVATE may be specified, in which case a new IPC object
61 An integer constant may be specified.
62 If no IPC object corresponding
65 is specified and the IPC_CREAT bit is set in
67 a new one will be created.
71 may be used to generate a key from a pathname.
74 The mode of a newly created IPC object is determined by
75 which are set by ORing these constants into the
80 Read access for owner.
82 Write access for owner.
84 Read access for group.
86 Write access for group.
88 Read access for other.
90 Write access for other.
93 .\" XXX - we should also mention how uid, euid, and gid affect ownership
96 .\" end section about keys and modes
99 When creating a new shared memory segment,
101 indicates the desired size of the new segment in bytes.
103 of the segment may be rounded up to a multiple convenient to the
104 kernel (i.e., the page size).
106 Upon successful completion,
108 returns the positive integer identifier of a shared memory segment.
109 Otherwise, -1 is returned and
111 set to indicate the error.
119 .\" XXX What about ipcperm failing?
122 Size specified is greater than the size of the previously existing segment.
123 Size specified is less than the system imposed minimum, or greater than
124 the system imposed maximum.
126 No shared memory segment was found matching
128 and IPC_CREAT was not specified.
130 The kernel was unable to allocate enough memory to
133 IPC_CREAT and IPC_EXCL were specified, and a shared memory segment