maxfiles_lim(5)                                             maxfiles_lim(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      maxfiles_lim - hard maximum number of file descriptors per process

 VALUES    [Toc]    [Back]
    Failsafe
      1024

    Default    [Toc]    [Back]
      4096

    Allowed values    [Toc]    [Back]
      The minimum value allowed is 32.  The maximum value allowed is
      1048576, or 1M.  The value is further constrained in that it must be
      equal or greater than the soft limit, maxfiles, and it should be less
      than or equal to half the value of the maximum system-wide number of
      file descriptors:

           nfile (maxfiles <= maxfiles_lim <= nfile/2).

      Specify a positive integer value.

    Recommended values    [Toc]    [Back]
      At runtime, a warning will be issued if the tunable is set to a value
      greater than 409600, or 400K.  This is beyond the tested limit.

      At runtime, a warning will be issued if the value is not a multiple of
      the file descriptor chunk (multiple of 8) size.  This is not a serious
      warning, just an information message for the administrator.

 DESCRIPTION    [Toc]    [Back]
      maxfiles_lim specifies the system hard limit for the number of file
      descriptors that a process is allowed to have for open files at any
      given time.  It is possible for a nonsuperuser process to increase its
      soft limit up to this hard limit.

    Who Is Expected to Change This Tunable?
      Anyone expecting to run applications using large numbers of file
      descriptors.

    Restrictions on Changing    [Toc]    [Back]
      The maxfiles_lim tunable is dynamic (tuning will take effect
      immediately on the running system).

      Dynamic changes affect all existing processes in the system except:

      +  Processes that have more file descriptors allocated than allowed by
         the new limit,

      +  Processes that have specifically set their limits through a call to
         setrlimit() or ulimit().




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






 maxfiles_lim(5)                                             maxfiles_lim(5)
                          Tunable Kernel Parameters



    When Should the Value of This Tunable Be Raised?
      The tunable should be increased when large numbers of file descriptors
      are expected to be open by several processes.

    What are the Side Effects of Raising the Value?
      There is no immediate effect of raising the value of maxfiles_lim.
      However, doing so allows any process to allocate more file
      descriptors, potentially consuming more system memory.

    When Should the Value of This Tunable Be Lowered?
      The value should be lowered to limit the number of open file
      descriptors per process on a system and reduce system memory
      consumption.

    What are the Side Effects of Lowering the Value?
      Lowering the value of maxfiles_lim bounds memory consumption due to
      file descriptors for processes that are not already over the new
      limit.

    What Other Tunable Values Should Be Changed at the Same Time?
      The value assigned to maxfiles must be less than or equal to the value
      of maxfiles_lim.

      The value of nfile must be equal to or greater than two times the
      value of maxfiles_lim.

      Kernel checks during tunable setting ensure these restrictions.

 WARNINGS    [Toc]    [Back]
      For values greater than 65535, compatibility for the obsolescent
      pstat_getfile() will be affected.  For correct operation, all
      applications must use pstat_getfile2() instead of pstat_getfile().  If
      the system still has applications using pstat_getfile(), setting
      maxfiles_lim to 65535 or less will maintain compatibility, unless the
      process being queried has used setrlimit() to change its maximum limit
      of open files to a value greater than 65535.

      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.





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






 maxfiles_lim(5)                                             maxfiles_lim(5)
                          Tunable Kernel Parameters



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

 SEE ALSO    [Toc]    [Back]
      kctune(1M), sam(1M), setrlimit(2), gettune(2), settune(2), pstat(2),
      ulimit(2), maxfiles(5), nfile(5).


 Hewlett-Packard Company            - 3 -      HP-UX 11i Version 2: Sep 2004