msgtql(5)msgtql(5)NAMEmsgtql - maximum number of System V IPC messages in the system at any
time
VALUES
Default
Failsafe
Allowed values
Recommended values
The largest number of messages expected.
DESCRIPTION
The tunable specifies the maximum total system-wide individual messages
across all message queues. Every message has a header to specify mes‐
sage type and location and the total number of headers is limited by
Note that if a system call attempts to exceed the limit imposed by it
will block until message space becomes available or return if is set.
Other kernel tunables may limit the maximum number of messages sup‐
ported. Limiting factors can be the maximum number of bytes in a
queue, and the maximum allowable total combined size, in bytes, in the
system.
For more information about System V message queues, refer to the sec‐
tion of the mesg(5) manpage.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
This tunable is dynamic. Changes to to this tunable take effect imme‐
diately.
When Should the Value of This Tunable Be Raised?
Raise this tunable if applications block too frequently in requiring
more total messages be held in the kernel message queues.
What are the Side Effects of Raising the Value?
Raising this value increases the possible number of messages which may
be queued at any point in time. This can result in msgsnd(2) having to
block less frequently. Since message queue headers are stored in ker‐
nel memory, that memory is unavailable for use by other system ser‐
vices.
When Should the Value of This Tunable Be Lowered?
Lower this tunable when applications no longer require as many total
messages.
What are the Side Effects of Lowering the Value?
Lowering the value increases the risk of application failure due to the
inability to send more messages. Lowering the tunable has no effect on
any queued messages, even if the new tunable value is less than the
number of queued messages. However, no new messages may be queued
until the number of messages falls below the setting of
What Other Tunable Values Should Be Changed at the Same Time?
All the System V message queue tunables are interrelated and should be
treated as independent variables. The set must be evaluated as a sys‐
tem to ensure the tunables reflect the application requirements. The
message tunables include and Specifically, the and tunables may need to
be adjusted along with the tunable.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parame‐
ter may be removed or have its meaning changed in future releases of
HP-UX.
System resource limits (such as, memory) may limit the number and/or
total size of queued messages. These system limits may be encountered
before the limit values of the msgtql and msgmbs tunables.
Installation of optional kernel software, from HP or other vendors, may
cause changes to tunable parameter values. After installation, some
tunable parameters may no longer be at the default or recommended val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
AUTHOR
was developed by AT&T.
SEE ALSOmsgsnd(2), mesg(5), msgmnb(5), msgmni(5), msgmbs(5).
Tunable Kernel Parameters msgtql(5)
