maxfiles_lim.5 (2010 09)

m
maxfiles_lim(5) maxfiles_lim(5)
(Tunable Kernel Parameters)
NAME
maxfiles_lim - hard maximum number of file descriptors per process
VALUES
Failsafe
1024
Default
4096
Allowed values
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.
Specify a positive integer value.
Recommended values
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
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
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().
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 pro-
cess 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.
Kernel checks during tunable setting ensure these restrictions.
WARNINGS
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
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1