tunables.conf(5)              File Formats Manual             tunables.conf(5)

NAME
       tunables.conf - tunables configuration file

SYNOPSIS
       /etc/tunables.conf

DESCRIPTION
       Tunables are a feature in the GNU C Library that allows application
       authors and distribution maintainers to alter the runtime library
       behavior to match their workload.

       The file is parsed by ldconfig(8) and the results stored in
       /etc/ld.so.cache.  The resulting data is read when the program starts
       execution.

       Each line in the file /etc/tunables.conf specifies a tunable, a
       directive, or a filter.

   Tunables
       A tunable is specified with a string of the form name=value.

       For a list of supported tunables, please consult the glibc manual that
       corresponds to your installed version of glibc, or run the following
       command:

           $ ld.so --list-tunables;

   Directives
       include path
              The syntax allows lines to start with the keyword include
              followed by a glob(7) pattern.  Files matching that pattern will
              be processed as if their contents were included at that point.

   Modifiers
       Each line may include zero or more keywords or symbols at the
       beginning, which affect how each tunable affects each processes.  The
       keywords must be separated by whitespace, but the symbols need not be.

       overridable
       +      Allow the tunable to be overridden by the GLIBC_TUNABLES
              environment variable when the process runs (this is the
              default).

       nonoverridable
       -      Do not allow the tunable to be overridden by the environment
              variable.

       onlysecure
       @      The tunable applies only to AT_SECURE processes, such as one
              started from a set-user-ID program, or one with elevated
              capabilities.

       nonsecure
       $      The tunable applies only to non-AT_SECURE processes (this is the
              default).

       anysecure
       *      The tunable applies to both AT_SECURE and non-AT_SECURE
              processes.

   Filters
       Filters limit the tunables following it.  The effects of a filter are
       terminated by any of the following:

       o  The end of the file.
       o  The end of an included file.
       o  An include directive.
       o  A new (possibly empty) filter.

       The syntax is:

           [filter:pattern]

       proc   The proc filter limits the following tunables to processes whose
              name matches the pattern.  The pattern may be an absolute path
              or just the base name.

       A filter can also be empty: [].  Such a filter has no effects.

FILES
       /etc/tunables.conf

       /etc/ld.so.cache
              Cached copy of tunables.

EXAMPLES
       Example configuration file:

           glibc.malloc.arenas_max=5
           onlysecure glibc.malloc.arenas_max=1
           -glibc.pthread.rseq=1
           [proc:/bin/bad.program]
           -glibc.pthread.rseq=0
           [proc:some.program]
           -glibc.malloc.mmap_threshold=65536

SEE ALSO
       ld.so(8), ldconfig(8)

Linux man-pages 6.19              2026-08-25                  tunables.conf(5)