.TH tunables.conf 5 2026-08-25 "Linux man-pages 6.20"
.SH NAME
tunables.conf \- tunables configuration file
.SH SYNOPSIS
.nf
.B /etc/tunables.conf
.fi
.SH 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.
.P
The file is parsed by
.BR \%ldconfig (8)
and the results stored in
.IR /etc/ld.so.cache .
The resulting data is read when the program starts execution.
.P
Each line in the file
.I /etc/tunables.conf
specifies
a tunable,
a directive,
or a filter.
.SS Tunables
A tunable is specified with a string of the form
.IB name = value \f[R].\f[]
.P
For a list of supported tunables,
please consult the glibc manual
that corresponds to your installed version of glibc,
or run the following command:
.P
.in +4n
.EX
.RB $ \~ld.so\~\-\-list\-tunables ;
.EE
.SS Directives
.TP
.BI include\~ path
The syntax allows lines to start with the keyword
.B include
followed by a
.BR \%glob (7)
pattern.
Files matching that pattern will be processed
as if their contents were included at that point.
.SS 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.
.TP
.B overridable
.TQ
.B +
Allow the tunable to be overridden by the
.B GLIBC_TUNABLES
environment variable when the process runs
(this is the default).
.TP
.B nonoverridable
.TQ
.B \-
Do not allow the tunable to be overridden by the environment variable.
.TP
.B onlysecure
.TQ
.B @
The tunable applies only to
.B AT_SECURE
processes,
such as one started from a set-user-ID program,
or one with elevated capabilities.
.TP
.B nonsecure
.TQ
.B $
The tunable applies only to
.RB non- AT_SECURE
processes (this is the default).
.TP
.B anysecure
.TQ
.B *
The tunable applies to both
.B AT_SECURE
and
.RB non- AT_SECURE
processes.
.SS Filters
Filters limit the tunables following it.
The effects of a filter are terminated by
any of the following:
.IP \[bu] 3
The end of the file.
.PD 0
.IP \[bu]
The end of an included file.
.IP \[bu]
An
.B include
directive.
.IP \[bu]
A new (possibly empty) filter.
.PD
.P
The syntax is:
.P
.in +4n
.EX
.BI [ filter : pattern ]
.EE
.in
.TP
.B proc
The
.B 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.
.P
A filter can also be empty:
.BR [] .
Such a filter has no effects.
.SH FILES
.TP
.I /etc/tunables.conf
.TP
.I /etc/ld.so.cache
Cached copy of tunables.
.SH EXAMPLES
Example configuration file:
.P
.in +4n
.EX
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
.EE
.in
.SH SEE ALSO
.BR ld.so (8),
.BR ldconfig (8)