NAME
mesg — enable or disable System V IPC messages at boot time
VALUES
Allowed values
1 (on)
or
0 (off)
DESCRIPTION
The
mesg
tunable is a "switch" designed to enable the entire System V IPC message subsystem.
It not only allows user access, but when disabled, memory space will
not
be reserved on system boot, and the System V messaging system will be totally removed.
However, the default state is enabled so the system exists after the first
cold install.
Considering the minimal impact for the default tunable values, a disabled message
system will be the exception.
Overview
A System V message is just a sequence of bytes that can be passed
between cooperating processes via a message queue.
Messages can be of any length (up to a kernel-tunable maximum) and
can be "typed" with a process-specified number.
Each message queue has a unique ID but can contain any mixture of
message types.
The process receiving a message can get the "first" message (FIFO),
the first of a specified type, the first of a group of types or
even wait for a specific type to appear.
Message passing between processes is supported by shared memory and
globally defined data structures which each process must use.
Message queues are implemented as linked lists in shared memory.
Each message in a queue consists of an ID, a header (links, type,
size and address) and one or more contiguous "segments" of reserved
memory space.
As messages are added and removed, the message resource map
tracks available free space.
The size of the resource map will help determine the potential
fragmentation of the reserved shared memory.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
What Are the Side Effects of Turning the Tunable Off?
Memory space will
not
be reserved on system boot, and the System V messaging system will
be totally removed.
What Other Tunable Values Should Be Changed at the Same Time?
All the System V IPC Message subsystem tunables are interrelated
and should
not
be treated as independent variables.
The set of eight tunables must be evaluated as a system to ensure they
reflect the application requirements.
The
mesg
tunables include
msgmap,
msgmax,
msgmnb,
msgmni,
msgseg,
msgssz,
and
msgtql.
WARNINGS
All HP-UX kernel tunable parameters are release specific.
This parameter may be removed or have its meaning changed in
future releases of HP-UX.
AUTHOR
mesg
was developed by AT&T.
SEE ALSO
msgmap(5),
msgmax(5),
msgmnb(5),
msgmni(5),
msgseg(5),
msgssz(5),
msgtql(5).
Printable version
