ipcs — report
System V interprocess communication facilities status
The ipcs program provides information on
System V interprocess communication (IPC) facilities on the system.
The options are as follows:
-a- Show the maximum amount of information possible when displaying active
message queues, shared memory segments, and semaphores. This is shorthand
for specifying the
-b, -c,
-o, -p, and
-t options.
-b- Show the maximum allowed sizes for active message queues, shared memory
segments, and semaphores. The “maximum allowed size” is the
maximum number of bytes in a message on a message queue, the size of a
shared memory segment, or the number of semaphores in a set of
semaphores.
-c- Show the creator's name and group for active message queues, shared memory
segments, and semaphores.
-M- Display system information about shared memory.
-m- Display information about active shared memory segments.
-o- Show outstanding usage for active message queues, and shared memory
segments. The “outstanding usage” is the number of messages
in a message queue, or the number of processes attached to a shared memory
segment.
-p- Show the PID information for active message queues, shared memory
segments, and semaphores. The “PID
information” is the last process to send a
message to or receive a message from a message queue, the last process to
attach to or detach a shared memory segment, or the process that created a
semaphore.
-Q- Display system information about messages queues.
-q- Display information about active message queues.
-S- Display system information about semaphores.
-s- Display information about active semaphores.
-T- Display system information about message queues, shared memory segments,
and semaphores. This is shorthand for specifying the
-M, -Q, and
-S options.
-t- Show access times for active message queues, shared memory segments, and
semaphores. The access times is the time of the last control operation on
an IPC object, the last send or receive of a message, the last attach or
detach of a shared memory segment, or the last operation on a
semaphore.
If none of the -M,
-m, -Q,
-q, -S,
-s, or -T options are
specified, information about all active IPC facilities is listed.
The output generated by ipcs if passed the
-M, -Q, and
-S options is self-explanatory. For the other
options, the output consists of a series of columns depending on the
facility in question as well as which of the various supported flags were
given.
The meaning of each column as identified by the column heading is
as follows:
- T
- The type of facility, identified as:
- m
- shared memory segment
- s
- semaphore
- q
- message queue
- ID
- The identifier, suitable to be passed to, e.g.,
ipcrm(1).
- KEY
- The key passed to, e.g.,
msgget(2),
semget(2), or
shmget(2); often created
using ftok(3).
- MODE
- A string of 11 characters representing the access mode and flags for the
facility.
On NetBSD, the first two characters
are always ‘-’.
The remaining 9 characters are similar to typical file
permissions in that three characters each refer to owner-, group-, and
other permissions of the facility entry with the following meaning:
- r
- read permission
- w
- write permission
- a
- alter permission (the ability to change control information such as
the owner or permissions)
- OWNER
- The user name (or, if no user name can be found, UID) of the owner of the
facility entry.
- GROUP
- The group name (or, if no group name can be found, GID) of the group owner
of the facility entry.
- CREATOR
- The user name (or, if no user name can be found, UID) of the creator of
the facility entry.
- CGROUP
- The group name (or, if no group name can be found, GID) of the creator
group owner of the facility entry.
Following this, the columns printed will differ for each of the
facilities.
Times are displayed as if with
strftime(3)
‘%k:%M:%S’ format (no leading zero for
the hours value) in the time zone described by the
TZ environment variable or
/etc/localtime. If no time is available for the
given event, the string ‘no-entry’ is
used instead.
- CBYTES
- The total number of bytes left in the message queue.
- QNUM
- The number of messages left in the message queue.
- QBYTES
- The maximum number of bytes in the message queue.
- LSPID
- The PID of the last process to send a message.
- LRPID
- The PID of the last process to receive a message.
- STIME
- The time of last
msgsend(2).
- RTIME
- The time of last
msgrcv(2).
- CTIME
- The time the message queue was created or last modified.
- NATTCH
- The number of current attaches.
- SEGSZ
- The size of the shared memory segment in bytes.
- CPID
- The PID of the process that created the shared memory segment.
- LPID
- The PID of the last shm operation.
- ATIME
- The time of last
shmat(2).
- DTIME
- The time of last
shmdt(2).
- CTIME
- The time the shared memory segment was created or last modified.
- NSEMS
- The number of semaphores in the set.
- OTIME
- The time of last
semop(2).
- CTIME
- The time the semaphore set was created or last modified.
System data structures may change while
ipcs is running; the output of
ipcs is not guaranteed to be consistent.
ipcrm(1),
msgctl(2),
msgget(2),
msgrcv(2),
msgsnd(2),
semctl(2),
semget(2),
semop(2),
shmat(2),
shmctl(2),
shmdt(2),
shmget(2),
ftok(3)
The first two characters of the MODE are always
set to ‘-’ on
NetBSD. On other platforms, these characters may
indicate additional state information about the given facility.