1 .\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
3 .\" Permission is granted to make and distribute verbatim copies of this
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7 .\" Permission is granted to copy and distribute modified versions of this
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9 .\" entire resulting derived work is distributed under the terms of a
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12 .\" Since the Linux kernel and libraries are constantly changing, this
13 .\" manual page may be incorrect or out-of-date. The author(s) assume no
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17 .\" which is licensed free of charge, as they might when working
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23 .\" FIXME There is now duplication of some of the information
24 .\" below in semctl.2, msgctl.2, and shmctl.2 -- MTK, Nov 04
25 .TH SVIPC 7 2009-01-26 "Linux" "Linux Programmer's Manual"
27 svipc \- System V interprocess communication mechanisms
30 .B #include <sys/types.h>
31 .B #include <sys/ipc.h>
32 .B #include <sys/msg.h>
33 .B #include <sys/sem.h>
34 .B #include <sys/shm.h>
37 This manual page refers to the Linux implementation of the System V
38 interprocess communication (IPC) mechanisms:
39 message queues, semaphore sets, and shared memory segments.
40 In the following, the word
42 means an instantiation of one among such mechanisms.
43 .SS Resource Access Permissions
44 For each resource, the system uses a common structure of type
46 to store information needed in determining permissions to perform an
50 structure includes the following members:
55 uid_t cuid; /* creator user ID */
56 gid_t cgid; /* creator group ID */
57 uid_t uid; /* owner user ID */
58 gid_t gid; /* owner group ID */
59 unsigned short mode; /* r/w permissions */
68 structure defines, with its lower 9 bits, the access permissions to the
69 resource for a process executing an IPC system call.
70 The permissions are interpreted as follows:
83 Bits 0100, 0010, and 0001 (the execute bits) are unused by the system.
90 The same system header file also defines the following symbolic
94 Create entry if key doesn't exist.
100 Error if request must wait.
109 Set resource options.
112 Get resource options.
118 type, while all the other symbolic constants are flag fields and can
123 A message queue is uniquely identified by a positive integer
125 and has an associated data structure of type
126 .IR "struct msqid_ds" ,
129 containing the following members:
134 struct ipc_perm msg_perm;
135 msgqnum_t msg_qnum; /* no of messages on queue */
136 msglen_t msg_qbytes; /* bytes max on a queue */
137 pid_t msg_lspid; /* PID of last msgsnd(2) call */
138 pid_t msg_lrpid; /* PID of last msgrcv(2) call */
139 time_t msg_stime; /* last msgsnd(2) time */
140 time_t msg_rtime; /* last msgrcv(2) time */
141 time_t msg_ctime; /* last change time */
148 structure that specifies the access permissions on the message
152 Number of messages currently on the message queue.
155 Maximum number of bytes of message text allowed on the message
159 ID of the process that performed the last
164 ID of the process that performed the last
180 system call that changed a member of the
184 A semaphore set is uniquely identified by a positive integer
186 and has an associated data structure of type
187 .IR "struct semid_ds" ,
190 containing the following members:
195 struct ipc_perm sem_perm;
196 time_t sem_otime; /* last operation time */
197 time_t sem_ctime; /* last change time */
198 unsigned long sem_nsems; /* count of sems in set */
205 structure that specifies the access permissions on the semaphore
216 system call that changed a member of the above structure or of one
217 semaphore belonging to the set.
220 Number of semaphores in the set.
221 Each semaphore of the set is referenced by a nonnegative integer
227 A semaphore is a data structure of type
229 containing the following members:
234 int semval; /* semaphore value */
235 int sempid; /* PID for last operation */
236 .\" unsigned short semncnt; /* nr awaiting semval to increase */
237 .\" unsigned short semzcnt; /* nr awaiting semval = 0 */
243 Semaphore value: a nonnegative integer.
246 ID of the last process that performed a semaphore operation
250 .\"Number of processes suspended awaiting for
255 .\"Number of processes suspended awaiting for
258 .SS Shared Memory Segments
259 A shared memory segment is uniquely identified by a positive integer
261 and has an associated data structure of type
262 .IR "struct shmid_ds" ,
265 containing the following members:
270 struct ipc_perm shm_perm;
271 size_t shm_segsz; /* size of segment */
272 pid_t shm_cpid; /* PID of creator */
273 pid_t shm_lpid; /* PID, last operation */
274 shmatt_t shm_nattch; /* no. of current attaches */
275 time_t shm_atime; /* time of last attach */
276 time_t shm_dtime; /* time of last detach */
277 time_t shm_ctime; /* time of last change */
284 structure that specifies the access permissions on the shared memory
288 Size in bytes of the shared memory segment.
291 ID of the process that created the shared memory segment.
294 ID of the last process that executed a
301 Number of current alive attaches for this shared memory segment.
316 system call that changed