HP-UX 11.x Operating Systems - Changing the POSIX Shell's ulimit -n (File Descriptor) Setting.

Overview

HP-UX 11.x Operating Systems - Changing the POSIX Shell's ulimit -n (File Descriptor) Setting.

Procedures

HP-UX 11.x Operating Systems - Changing the POSIX Shell's ulimit -n (File Descriptor) Setting Issue This document provides information and examples on how to change the POSIX shell's ulimit -n parameter (the resource limit for the number of per-process file descriptors allowed in that shell's environment). Solution ulimit usage will be shell-specific. For use with the POSIX shell, refer to the sh-posix(1) manual page and search for ulimit . To display the current value of the file descriptor setting in ulimit : # ulimit -n 4096 To display the hard limit of the file descriptor setting: # ulimit -Hn 4096 To change the soft limit of the file descriptor setting: # ulimit -n 2048 To confirm the new value following the change: # ulimit -n 2048 To change the hard limit of the file descriptor setting: # ulimit -Hn 2048 To confirm the new value following the change: # ulimit -Hn 2048 We were able to decrease the value of the file descriptor setting. But, if we attempt to increase it to greater than 4096 , then an error would be returned: # ulimit -n 8192 sh: ulimit: The specified value exceeds the user's allowable limit. This is because our hard limit is also not set to unlimited. Thus, will try to increase that to unlimited: # ulimit -Ha n 8192 sh: ulimit: The specified value exceeds the user's allowable limit. Again, we saw the error. This is because soft limit of file descriptor setting depends upon the maxfiles kernel tunable, and the hard limit of the file descriptor setting depends upon the maxfiles_lim kernel tunable: maxfiles < or = maxfiles_lim softlimit < or = hard limit # kctune -q maxfiles Tunable   Value  Expression   maxfiles   4096  Default # kctune -q maxfiles _lim Tunable       Value  Expression  Changes maxfiles_lim   4096  Default     Immed The maxfiles kernel tunable is presently 4096 and maxfiles_lim = 4096 . Thus, if we want to set the ulimit file descriptor setting to more than 4096 , we first need to increase the values of the maxfiles and maxfiles_lim kernel tunables: # kctune maxfiles=8192 NOTE:    The configuration being loaded contains the following change(s)          that cannot be applied immediately and which will be held for          the next boot:       -- The tunable maxfiles cannot be changed in a dynamic fashion.        * The automatic 'backup' configuration has been updated.        * The requested changes have been saved, and will take effect at          next boot. Tunable                Value  Expression   maxfiles  (now)         2048  Default                (next boot)   8192  8192   NOTE : changing the maxfiles tunable requires a restart of system. # kctune maxfiles _lim=8192 WARNING: The automatic 'backup' configuration currently contains the          configuration that was in use before the last reboot of this          system.      ==> Do you wish to update it to contain the current configuration          before making the requested change? y        * The automatic 'backup' configuration has been updated.        * The requested changes have been applied to the currently          running system. Tunable                 Value  Expression  Changes maxfiles_lim  (before)   4096  Default     Immed               (now)      8192  8192         Now, the nofiles descriptor value may be changed in ulimit after a restart of system. Before setting the soft limit, we would need to increase the hard limit: # ulimit -Hd 8192 Confirm the hard limit change: # ulimit - Hn 8292 Now, we will be able to change the soft limit of the file descriptor setting with ulimit : # ulimit -n 8192 Confirm the changes: # ulimit - n 8192 NOTE: Changing the maxfiles and maxfiles_lim kernel parameters also confirms that the value of soft limit and the hard limit for the file descriptor setting in ulimit is defaulted to the new values of maxfiles and maxfiles_lim after a system restart. If we need to set the specific value for all users, we can set this in /etc/profile . If we want to do this for a particular user, then we can edit their .profile , adding a line that has the following format: ulimit -n new_value

Keywords.

ulimit.