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ipcs - show information on IPC facilities
ipcs shows information on System V inter-process communication
facilities. By default it shows information about all three resources: shared
memory segments, message queues, and semaphore arrays.
- -i, --id id
- Show full details on just the one resource element identified by
id. This option needs to be combined with one of the three resource
options: -m, -q or -s.
- -h, --help
- Display help text and exit.
- -V, --version
- Display version information and exit.
- -m, --shmems
- Write information about active shared memory segments.
- -q, --queues
- Write information about active message queues.
- -s, --semaphores
- Write information about active semaphore sets.
- -a, --all
- Write information about all three resources (default).
Of these options only one takes effect: the last one specified.
- -c, --creator
- Show creator and owner.
- -l, --limits
- Show resource limits.
- -p, --pid
- Show PIDs of creator and last operator.
- -t, --time
- Write time information. The time of the last control operation that
changed the access permissions for all facilities, the time of the last
msgsnd(2) and msgrcv(2) operations on message queues, the
time of the last shmat(2) and shmdt(2) operations on shared
memory, and the time of the last semop(2) operation on
- -u, --summary
- Show status summary.
These affect only the -l (--limits) option.
- -b, --bytes
- Print sizes in bytes.
- Print sizes in human-readable format.
The Linux ipcs utility is not fully compatible to the POSIX ipcs utility. The
Linux version does not support the POSIX -a, -b and -o
options, but does support the -l and -u options not defined by
POSIX. A portable application shall not use the -a, -b,
-o, -l, and -u options.
The current implementation of ipcs obtains information about available
IPC resources by parsing the files in /proc/sysvipc. Before util-linux
version v2.23, an alternate mechanism was used: the IPC_STAT command of
msgctl(2), semctl(2), and shmctl(2). This mechanism is
also used in later util-linux versions in the case where /proc is
unavailable. A limitation of the IPC_STAT mechanism is that it can only
be used to retrieve information about IPC resources for which the user has
The ipcs command is part of the util-linux package and is available from