+++ /dev/null
-.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
-.\"
-.\" %%%LICENSE_START(VERBATIM)
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.\" FIXME . There is now duplication of some of the information
-.\" below in semctl.2, msgctl.2, and shmctl.2 -- MTK, Nov 04
-.\"
-.\" FIXME . Ultimately, there should probably be
-.\" svmq_overview(7), svshm_overview(7), and sem_overview(7)
-.\" that provide an overview of each System V IPC mechanism.
-.\" In that case:
-.\" * Those files should add a discussion of the /proc/sysvipc
-.\" interfaces.
-.\" * Documentation of the various /proc interfaces should move into
-.\" those files (from proc(5)), and references in the various *.2
-.\" pages that refer to the /proc files should be adjusted.
-.\" * The only part that uniquely belongs in svipc(7) is perphaps
-.\" the discussion of ipc_perm.
-.\"
-.TH SVIPC 7 2014-09-21 "Linux" "Linux Programmer's Manual"
-.SH NAME
-svipc \- System V interprocess communication mechanisms
-.SH SYNOPSIS
-.nf
-.B #include <sys/msg.h>
-.B #include <sys/sem.h>
-.B #include <sys/shm.h>
-.fi
-.SH DESCRIPTION
-This manual page refers to the Linux implementation of the System V
-interprocess communication (IPC) mechanisms:
-message queues, semaphore sets, and shared memory segments.
-In the following, the word
-.I resource
-means an instantiation of one among such mechanisms.
-.SS Resource access permissions
-For each resource, the system uses a common structure of type
-.I "struct ipc_perm"
-to store information needed in determining permissions to perform an
-IPC operation.
-The
-.I ipc_perm
-structure includes the following members:
-.in +4n
-.nf
-
-struct ipc_perm {
- uid_t cuid; /* creator user ID */
- gid_t cgid; /* creator group ID */
- uid_t uid; /* owner user ID */
- gid_t gid; /* owner group ID */
- unsigned short mode; /* r/w permissions */
-};
-.fi
-.in
-.PP
-The
-.I mode
-member of the
-.I ipc_perm
-structure defines, with its lower 9 bits, the access permissions to the
-resource for a process executing an IPC system call.
-The permissions are interpreted as follows:
-.sp
-.nf
- 0400 Read by user.
- 0200 Write by user.
-.sp .5
- 0040 Read by group.
- 0020 Write by group.
-.sp .5
- 0004 Read by others.
- 0002 Write by others.
-.fi
-.PP
-Bits 0100, 0010, and 0001 (the execute bits) are unused by the system.
-Furthermore,
-"write"
-effectively means
-"alter"
-for a semaphore set.
-.PP
-The same system header file also defines the following symbolic
-constants:
-.TP 14
-.B IPC_CREAT
-Create entry if key doesn't exist.
-.TP
-.B IPC_EXCL
-Fail if key exists.
-.TP
-.B IPC_NOWAIT
-Error if request must wait.
-.TP
-.B IPC_PRIVATE
-Private key.
-.TP
-.B IPC_RMID
-Remove resource.
-.TP
-.B IPC_SET
-Set resource options.
-.TP
-.B IPC_STAT
-Get resource options.
-.PP
-Note that
-.B IPC_PRIVATE
-is a
-.I key_t
-type, while all the other symbolic constants are flag fields and can
-be OR'ed into an
-.I int
-type variable.
-.SS Message queues
-A message queue is uniquely identified by a positive integer
-.RI "(its " msqid )
-and has an associated data structure of type
-.IR "struct msqid_ds" ,
-defined in
-.IR <sys/msg.h> ,
-containing the following members:
-.in +4n
-.nf
-
-struct msqid_ds {
- struct ipc_perm msg_perm;
- msgqnum_t msg_qnum; /* no of messages on queue */
- msglen_t msg_qbytes; /* bytes max on a queue */
- pid_t msg_lspid; /* PID of last msgsnd(2) call */
- pid_t msg_lrpid; /* PID of last msgrcv(2) call */
- time_t msg_stime; /* last msgsnd(2) time */
- time_t msg_rtime; /* last msgrcv(2) time */
- time_t msg_ctime; /* last change time */
-};
-.fi
-.in
-.TP 11
-.I msg_perm
-.I ipc_perm
-structure that specifies the access permissions on the message
-queue.
-.TP
-.I msg_qnum
-Number of messages currently on the message queue.
-.TP
-.I msg_qbytes
-Maximum number of bytes of message text allowed on the message
-queue.
-.TP
-.I msg_lspid
-ID of the process that performed the last
-.BR msgsnd (2)
-system call.
-.TP
-.I msg_lrpid
-ID of the process that performed the last
-.BR msgrcv (2)
-system call.
-.TP
-.I msg_stime
-Time of the last
-.BR msgsnd (2)
-system call.
-.TP
-.I msg_rtime
-Time of the last
-.BR msgrcv (2)
-system call.
-.TP
-.I msg_ctime
-Time of the last
-system call that changed a member of the
-.I msqid_ds
-structure.
-.SS Semaphore sets
-A semaphore set is uniquely identified by a positive integer
-.RI "(its " semid )
-and has an associated data structure of type
-.IR "struct semid_ds" ,
-defined in
-.IR <sys/sem.h> ,
-containing the following members:
-.in +4n
-.nf
-
-struct semid_ds {
- struct ipc_perm sem_perm;
- time_t sem_otime; /* last operation time */
- time_t sem_ctime; /* last change time */
- unsigned long sem_nsems; /* count of sems in set */
-};
-.fi
-.in
-.TP 11
-.I sem_perm
-.I ipc_perm
-structure that specifies the access permissions on the semaphore
-set.
-.TP
-.I sem_otime
-Time of last
-.BR semop (2)
-system call.
-.TP
-.I sem_ctime
-Time of last
-.BR semctl (2)
-system call that changed a member of the above structure or of one
-semaphore belonging to the set.
-.TP
-.I sem_nsems
-Number of semaphores in the set.
-Each semaphore of the set is referenced by a nonnegative integer
-ranging from
-.B 0
-to
-.IR sem_nsems\-1 .
-.PP
-A semaphore is a data structure of type
-.I "struct sem"
-containing the following members:
-.in +4n
-.nf
-
-struct sem {
- int semval; /* semaphore value */
- int sempid; /* PID for last operation */
-.\" unsigned short semncnt; /* nr awaiting semval to increase */
-.\" unsigned short semzcnt; /* nr awaiting semval = 0 */
-};
-.fi
-.in
-.TP 11
-.I semval
-Semaphore value: a nonnegative integer.
-.TP
-.I sempid
-ID of the last process that performed a semaphore operation
-on this semaphore.
-.\".TP
-.\".I semncnt
-.\"Number of processes suspended awaiting for
-.\".I semval
-.\"to increase.
-.\".TP
-.\".I semznt
-.\"Number of processes suspended awaiting for
-.\".I semval
-.\"to become zero.
-.SS Shared memory segments
-A shared memory segment is uniquely identified by a positive integer
-.RI "(its " shmid )
-and has an associated data structure of type
-.IR "struct shmid_ds" ,
-defined in
-.IR <sys/shm.h> ,
-containing the following members:
-.in +4n
-.nf
-
-struct shmid_ds {
- struct ipc_perm shm_perm;
- size_t shm_segsz; /* size of segment */
- pid_t shm_cpid; /* PID of creator */
- pid_t shm_lpid; /* PID, last operation */
- shmatt_t shm_nattch; /* no. of current attaches */
- time_t shm_atime; /* time of last attach */
- time_t shm_dtime; /* time of last detach */
- time_t shm_ctime; /* time of last change */
-};
-.fi
-.in
-.TP 11
-.I shm_perm
-.I ipc_perm
-structure that specifies the access permissions on the shared memory
-segment.
-.TP
-.I shm_segsz
-Size in bytes of the shared memory segment.
-.TP
-.I shm_cpid
-ID of the process that created the shared memory segment.
-.TP
-.I shm_lpid
-ID of the last process that executed a
-.BR shmat (2)
-or
-.BR shmdt (2)
-system call.
-.TP
-.I shm_nattch
-Number of current alive attaches for this shared memory segment.
-.TP
-.I shm_atime
-Time of the last
-.BR shmat (2)
-system call.
-.TP
-.I shm_dtime
-Time of the last
-.BR shmdt (2)
-system call.
-.TP
-.I shm_ctime
-Time of the last
-.BR shmctl (2)
-system call that changed
-.IR shmid_ds .
-.SS IPC namespaces
-For a discussion of the interaction of System V IPC objects and
-IPC namespaces, see
-.BR namespaces (7).
-.SH SEE ALSO
-.BR ipcmk (1),
-.BR ipcrm (1),
-.BR ipcs (1),
-.BR ipc (2),
-.BR msgctl (2),
-.BR msgget (2),
-.BR msgrcv (2),
-.BR msgsnd (2),
-.BR semctl (2),
-.BR semget (2),
-.BR semop (2),
-.BR shmat (2),
-.BR shmctl (2),
-.BR shmdt (2),
-.BR shmget (2),
-.BR ftok (3),
-.BR namespaces (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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