The ipcs utility prints information about active inter-process communication facilities. The information that is displayed is controlled by the options supplied. Without options, information is printed in short format for message queues, shared memory, and semaphores that are currently active in the system.

The following options are supported:

-m

Prints information about active shared memory segments.

-q

Prints information about active message queues.

-s

Prints information about active semaphores.

If -m, -q, or -s are specified, information about only those indicated is printed. If none of these three is specified, information about all three is printed subject to these options:

-a

Uses all XCU5 print options. (This is a shorthand notation for -b, -c, -o, -p, and -t.)

-A

Uses all print options. (This is a shorthand notation for -b, -c, -i, -o, -p, and -t.)

-b

Prints information on biggest allowable size: maximum number of bytes in messages on queue for message queues, size of segments for shared memory, and number of semaphores in each set for semaphores. See below for meaning of columns in a listing.

-c

Prints creator's login name and group name. See below.

-D mtype

Displays, in hexadecimal and ASCII, the contents of all messages of type mtype found on any message queue that the user invoking ipcs has permission to read. If mtype is 0, all messages are displayed. If mtype is negative, all messages with type less than or equal to the absolute value of mtype are displayed. (See msgrcv(2) and msgsnap(2)).

-i

Prints number of ISM attaches to shared memory segments.

-o

Prints information on outstanding usage: number of messages on queue and total number of bytes in messages on queue for message queues and number of processes attached to shared memory segments.

-p

Prints process number information: process ID of last process to send a message, process ID of last process to receive a message on message queues, process ID of creating process, and process ID of last process to attach or detach on shared memory segments. See below.

-t

Prints time information: time of the last control operation that changed the access permissions for all facilities, time of last msgsnd(2) and last msgrcv(2) on message queues, time of last shmat(2) and last shmdt(2 ) on shared memory (see shmop(2)), time of last semop(2) on semaphores. See below.

The column headings and the meaning of the columns in an ipcs listing are given below. The letters in parentheses indicate the options that cause the corresponding heading to appear. "all" means that the heading always appears. Note: These options only determine what information is provided for each facility; they do not determine which facilities are listed.

T (all)

Type of the facility:

q

message queue

m

shared memory segment

s

semaphore

ID (all)

The identifier for the facility entry.

KEY (all)

The key used as an argument to msgget(2), semget(2), or shmget(2) to create the facility entry. (Note: The key of a shared memory segment is changed to IPC_PRIVATE when the segment has been removed until all processes attached to the segment detach it.)

MODE (all)

The facility access modes and flags: The mode consists of 11 characters that are interpreted as follows. The first two characters are:

R

A process is waiting on a msgrcv(2).

S

A process is waiting on a msgsnd(2).

D

The associated shared memory segment has been removed. It will disappear when the last process attached to the segment detaches it. (Note: If the shared memory segment identifier is removed via an IPC_RMID call to shmctl(2) before the process has detached from the segment with shmdt(2), the segment is no longer visible to ipcs and it will not appear in the ipcs output.)

C

The associated shared memory segment is to be cleared when the first attach is executed.

-

The corresponding special flag is not set.

The next nine characters are interpreted as three sets of three bits each. The first set refers to the owner's permissions; the next to permissions of others in the user-group of the facility entry; and the last to all others. Within each set, the first character indicates permission to read, the second character indicates permission to write or alter the facility entry, and the last character is currently unused.

The permissions are indicated as follows:

r

Read permission is granted.

w

Write permission is granted.

a

Alter permission is granted.

-

The indicated permission is not granted.

OWNER (all)

The login name of the owner of the facility entry.

GROUP (all)

The group name of the group of the owner of the facility entry.

CREATOR (a,A,c)

The login name of the creator of the facility entry.

CGROUP (a,A,c)

The group name of the group of the creator of the facility entry.

CBYTES (a,A,o)

The number of bytes in messages currently outstanding on the associated message queue.

QNUM (a,A,o)

The number of messages currently outstanding on the associated message queue.

QBYTES (a,A,b)

The maximum number of bytes allowed in messages outstanding on the associated message queue.

LSPID (a,A,p)

The process ID of the last process to send a message to the associated queue.

LRPID (a,A,p)

The process ID of the last process to receive a message from the associated queue.

STIME (a,A,t)

The time the last message was sent to the associated queue.

RTIME (a,A,t)

The time the last message was received from the associated queue.

CTIME (a,A,t)

The time when the associated entry was created or changed.

ISMATTCH (a,i)

The number of ISM attaches to the associated shared memory segments.

NATTCH (a,A,o)

The number of processes attached to the associated shared memory segment.

SEGSZ (a,A,b)

The size of the associated shared memory segment.

CPID (a,A,p)

The process ID of the creator of the shared memory entry.

LPID (a,A,p)

The process ID of the last process to attach or detach the shared memory segment.

ATIME (a,A,t)

The time the last attach was completed to the associated shared memory segment.

DTIME (a,A,t)

The time the last detach was completed on the associated shared memory segment.

NSEMS (a,A,b)

The number of semaphores in the set associated with the semaphore entry.

OTIME (a,A,t)

The time the last semaphore operation was completed on the set associated with the semaphore entry.

See environ(5) for descriptions of the following environment variables that affect the execution of ipcs: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.

TZ

Determine the timezone for the time strings written by ipcs.

/etc/group

group names

/etc/passwd

user names

See attributes(5) for descriptions of the following attributes:

ipcrm(1), msgget(2), msgids(2), msgrcv(2), msgsnap(2), msgsnd(2), semget(2), semids(2), semop(2), shmctl(2), shmget(2), shmids(2), shmop(2), attributes(5), environ( 5)

Things can change while ipcs is running. The information it gives is guaranteed to be accurate only when it was retrieved.