HP-UX Reference (11i v2 03/08) - 5 Miscellaneous Topics, 7 Device (Special) Files, 9 General Information, Index (vol 9)

n
nclist(5) nclist(5)
(Tunable Kernel Parameters)
NAME
nclist - number of cblocks for pty and tty data transfers
VALUES
Default
8292
Allowed Values
Minimum 132 and maximum limited by available memory.
DESCRIPTION
nclist specifies how many cblocks are allocated in the system. Data traffic is stored in
cblocks as
it passes through tty and pty devices.
The default value for
nclist, 8292, is based on a formula of 100
cblocks for system use in handling
traffic to the console, etc., plus an average of 16
cblocks per user session, assuming 512 user sessions.
cblocks are also used for serial connections other than login sessions, such as as SLIP connections,
UUCP transfers, terminal emulators, and such. If your system is using these other kinds of connections,
nclist should be increased accordingly.
If the
cblock pool is exhausted, data being passed through a tty or pty device might be lost because a
cblock was not available when it was needed. If this occurs, the WARNING: cblock exhaustion
has occurred n times (see termio(7)). message is placed in the system message buffer.
Who is expected to change this tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
When the kernel sends the error message
WARNING: cblock exhaustion has occurred n
times (see termio(7))., the system is running out of cblocks. This indicates that nclist
needs to be increased.
The minimum value for
nclist is 132. There is no maximum, but each cblock consumes 32 bytes of
resident (non-swappable) machine memory, so the value should be selected with this in mind.
What Are the Side Effects of Raising the Value of This Tunable?
More resident (non-swappable) machine memory is used.
When Should the Value of This Tunable Be Lowered?
This value should be lowered when a minimal system is being created.
What Are the Side Effects of Lowering the Value of This Tunable?
The system may run out of
cblocks.
What Other Tunables Should Be Changed at the Same Time?
None.
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
nclist was developed by HP.
SEE ALSO
termio(7).
Section 5−−190 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: August 2003