nclist(5)                                                         nclist(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      nclist - number of cblocks for pty and tty data transfers

 VALUES    [Toc]    [Back]
    Default
      8292

    Allowed Values    [Toc]    [Back]
      Minimum 132 and maximum limited by available memory.

 DESCRIPTION    [Toc]    [Back]
      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?
      Super users.

    Restrictions on Changing    [Toc]    [Back]
      Changes to this tunable take effect at the next reboot.

    When Should the Value of This Tunable Be Raised?
      The tunable value can be increased in the follwing instances:

           +  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 system may run slow for terminal I/O resulting in some
              data loss, without displaying a warning message.  Increasing
              the nclist value may solve this problem.

      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.





 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004






 nclist(5)                                                         nclist(5)
                          Tunable Kernel Parameters



    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    [Toc]    [Back]
      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.

      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
      values.  For information about the effects of installation on tunable
      values, consult the documentation for the kernel software being
      installed. For information about optional kernel software that was
      factory installed on your system, see HP-UX Release Notes at
      http://docs.hp.com.

 AUTHOR    [Toc]    [Back]
      nclist was developed by HP.

 SEE ALSO    [Toc]    [Back]
      kctune(1M), termio(7).


 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004