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7 .TH SHMGET 2 "Aug 14, 2006"
8 .SH NAME
9 shmget \- get shared memory segment identifier
10 .SH SYNOPSIS
11 .LP
12 .nf
13 #include <sys/types.h>
14 #include <sys/ipc.h>
15 #include <sys/shm.h>
17 \fBint\fR \fBshmget\fR(\fBkey_t\fR \fIkey\fR, \fBsize_t\fR \fIsize\fR, \fBint\fR \fIshmflg\fR);
18 .fi
20 .SH DESCRIPTION
21 .sp
22 .LP
23 The \fBshmget()\fR function returns the shared memory identifier associated
24 with \fIkey\fR.
25 .sp
26 .LP
27 A shared memory identifier and associated data structure and shared memory
28 segment of at least \fIsize\fR bytes (see \fBIntro\fR(2)) are created for
29 \fIkey\fR if one of the following are true:
30 .RS +4
31 .TP
32 .ie t \(bu
33 .el o
34 The \fIkey\fR argument is equal to \fBIPC_PRIVATE\fR.
35 .RE
36 .RS +4
37 .TP
38 .ie t \(bu
39 .el o
40 The \fIkey\fR argument does not already have a shared memory identifier
41 associated with it, and (\fIshmflg\fR\fB&IPC_CREAT\fR) is true.
42 .RE
43 .sp
44 .LP
45 Upon creation, the data structure associated with the new shared memory
46 identifier is initialized as follows:
47 .RS +4
48 .TP
49 .ie t \(bu
50 .el o
51 The values of \fBshm_perm.cuid\fR, \fBshm_perm.uid\fR, \fBshm_perm.cgid\fR, and
52 \fBshm_perm.gid\fR are set equal to the effective user \fBID\fR and effective
53 group ID, respectively, of the calling process.
54 .RE
55 .RS +4
56 .TP
57 .ie t \(bu
58 .el o
59 The access permission bits of \fBshm_perm.mode\fR are set equal to the access
60 permission bits of \fIshmflg\fR. \fBshm_segsz\fR is set equal to the value of
61 \fIsize\fR.
62 .RE
63 .RS +4
64 .TP
65 .ie t \(bu
66 .el o
67 The values of \fBshm_lpid\fR, \fBshm_nattch\fR \fBshm_atime\fR, and
68 \fBshm_dtime\fR are set equal to 0.
69 .RE
70 .RS +4
71 .TP
72 .ie t \(bu
73 .el o
74 The \fBshm_ctime\fR is set equal to the current time.
75 .RE
76 .sp
77 .LP
78 Shared memory segments must be explicitly removed after the last reference to
79 them has been removed.
80 .SH RETURN VALUES
81 .sp
82 .LP
83 Upon successful completion, a non-negative integer representing a shared memory
84 identifier is returned. Otherwise, \fB\(mi1\fR is returned and \fBerrno\fR is
85 set to indicate the error.
86 .SH ERRORS
87 .sp
88 .LP
89 The \fBshmget()\fR function will fail if:
90 .sp
91 .ne 2
92 .na
93 \fB\fBEACCES\fR\fR
94 .ad
95 .RS 10n
96 A shared memory identifier exists for \fIkey\fR but operation permission (see
97 \fBIntro\fR(2)) as specified by the low-order 9 bits of \fIshmflg\fR would not
98 be granted.
99 .RE
101 .sp
102 .ne 2
103 .na
104 \fB\fBEEXIST\fR\fR
105 .ad
106 .RS 10n
107 A shared memory identifier exists for \fIkey\fR but both
108 (\fIshmflg\fR\fB&IPC_CREAT\fR) and (\fIshmflg\fR\fB&IPC_EXCL\fR) are true.
109 .RE
111 .sp
112 .ne 2
113 .na
114 \fB\fBEINVAL\fR\fR
115 .ad
116 .RS 10n
117 The \fIsize\fR argument is less than the system-imposed minimum or greater than
118 the system-imposed maximum. See NOTES.
119 .sp
120 A shared memory identifier exists for \fIkey\fR but the size of the segment
121 associated with it is less than \fIsize\fR and \fIsize\fR is not equal to 0.
122 .RE
124 .sp
125 .ne 2
126 .na
127 \fB\fBENOENT\fR\fR
128 .ad
129 .RS 10n
130 A shared memory identifier does not exist for \fIkey\fR and
131 (\fIshmflg\fR\fB&IPC_CREAT\fR) is false.
132 .RE
134 .sp
135 .ne 2
136 .na
137 \fB\fBENOMEM\fR\fR
138 .ad
139 .RS 10n
140 A shared memory identifier and associated shared memory segment are to be
141 created but the amount of available memory is not sufficient to fill the
142 request.
143 .RE
145 .sp
146 .ne 2
147 .na
148 \fB\fBENOSPC\fR\fR
149 .ad
150 .RS 10n
151 A shared memory identifier is to be created but the system-imposed limit on the
152 maximum number of allowed shared memory identifiers system-wide would be
153 exceeded. See NOTES.
154 .RE
156 .SH ATTRIBUTES
157 .sp
158 .LP
159 See \fBattributes\fR(5) for descriptions of the following attributes:
160 .sp
162 .sp
163 .TS
164 box;
165 c | c
166 l | l .
167 ATTRIBUTE TYPE ATTRIBUTE VALUE
168 _
169 Interface Stability Standard
170 .TE
172 .SH SEE ALSO
173 .sp
174 .LP
175 \fBrctladm\fR(1M), \fBIntro\fR(2), \fBsetrctl\fR(2), \fBshmctl\fR(2),
176 \fBshmop\fR(2), \fBftok\fR(3C), \fBgetpagesize\fR(3C), \fBattributes\fR(5),
177 \fBstandards\fR(5)
178 .SH NOTES
179 .sp
180 .LP
181 The \fBproject.max-shm-memory\fR resource control restricts the total amount of
182 shared memory a project can allocate. The \fBzone.max-shm-memory\fR resource
183 control restricts the total amount of shared memory that can be allocated by a
184 zone. The system-imposed maximum on the size of a shared memory segment is
185 therefore a function of the sizes of any other shared memory segments the
186 calling project might have allocated that are still in use, as well as any
187 other shared memory segments allocated and still in use by processes in the
188 zone. For accounting purposes, segment sizes are rounded up to the nearest
189 multiple of the system page size. See \fBgetpagesize\fR(3C).
190 .sp
191 .LP
192 The system-imposed limit on the number of shared memory identifiers is
193 maintained on a per-project basis using the \fBproject.max-shm-ids\fR resource
194 control. The \fBzone.max-shm-ids\fR resource control restricts the total number
195 of shared memory identifiers that can be allocated by a zone.
196 .sp
197 .LP
198 See \fBrctladm\fR(1M) and \fBsetrctl\fR(2) for information about using resource
199 controls.