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rhel7-system-parameters-overview.md

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RHEL system parameters overview

This section provides some background on how system parameters are managed.

RHEL system parameters can be configured in several places with a well-defined precedence. The /etc/sysctl.conf file is intended for use by the "local" system administrator. Parameter settings in /etc/sysctl.conf have the highest precedence with respect to the value settings. Other locations where system configuration parameters are read in order of precedence are: /etc/sysctl.d/*.conf, /run/sysctl.d/*.conf and /usr/lib/sysctl.d/*.conf. There are other locations for system configuration parameters as well. See the man pages for sysctl and sysctl.d for more details.

NOTE: It is recommended that configuration parameter file names have a leading 2-digit number followed by a dash in order to clearly indicate the ordering in which the files should be processed at the time the machine is booted. (The files are processed in the lexical ordering of their names.)

The following observations apply to a default RHEL image. The specific VM you are using may be configured differently.

  • On a default RHEL image, the /etc/sysctl.conf file has nothing in it, and comments in /etc/sysctl.conf refer to using files in /usr/lib/sysctl.d.

  • On a default RHEL image, /usr/lib/sysctl.d has three files:

      ls /usr/lib/sysctl.d/
  00-system.conf  50-default.conf  60-libvirtd.conf

  • On a default RHEL image, none of the above files has anything in it having to do with vm.max_map_count.

  • On a default RHEL image, there is nothing in /run/sysctl.d/ (The sysctl.d directory does not exist.) The /etc/sysctl.d has only the file, 99-sysctl.conf, but that file has nothing in it except the preface comments.