tunables.conf(5)

💖 tunables.conf — the vibes manual 💖

okay bestie, welcome to tunables.conf(5), straight out of the File Formats Manual section of your local man-pages situation. this is the file that tells your runtime library how to act, and honestly? it's giving quiet power. let's get into it 🎀

✨ NAME ✨

tunables.conf — the tunables configuration file. that's it, that's the name, she's simple and she knows it 💅

✨ SYNOPSIS ✨

/etc/tunables.conf

✨ DESCRIPTION ✨

so Tunables are a feature in the GNU C Library that lets application authors and distribution maintainers change how the runtime library behaves, so it actually matches their workload. customizable queen behavior, we love to see it 💜

this file gets parsed by ldconfig(8), and the results get stored in /etc/ld.so.cache. then, when a program starts executing, that resulting data gets read. so it's like... the file whispers, ldconfig writes it down, and every program reads the notes later. iconic pipeline honestly 🦋

every single line in /etc/tunables.conf is one of three things: a tunable, a directive, or a filter. no cap.

🌸 Tunables 🌸

a tunable is written as a string shaped like name=value. that's the whole format, that's the assignment, periodt.

for the list of supported tunables? bestie, pls consult the glibc manual that matches your installed version of glibc, or just run this:

$ ld.so --list-tunables;

(yes the semicolon is in there, she's part of the command, leave her alone 💀)

🌸 Directives 🌸

• include path — the syntax lets a line start with the keyword include followed by a glob(7) pattern. every file matching that pattern gets processed as if its contents were included right at that point. it's copy-paste energy without the copy-paste 💫

🌸 Modifiers 🌸

each line can have zero or more keywords or symbols at the beginning, and those change how each tunable affects each process. the keywords must be separated by whitespace — but the symbols do not need to be. rude little asymmetry but okay, we adapt ✨

• overridable, + — lets the tunable be overridden by the GLIBC_TUNABLES environment variable when the process runs. this is the default, btw 👑
• nonoverridable, - — do not let the environment variable override this one. hands off, she said what she said 🚫
• onlysecure, @ — the tunable applies only to AT_SECURE processes, like one started from a set-user-ID program, or one with elevated capabilities. exclusive club, velvet rope, iykyk 🎀
• nonsecure, $ — the tunable applies only to non-AT_SECURE processes. this is the default too 💅
• anysecure, * — the tunable applies to both AT_SECURE and non-AT_SECURE processes. everybody's invited, she's inclusive 🌈

🌸 Filters 🌸

filters limit the tunables that come after them. and the effects of a filter get terminated by any one of these:

• the end of the file.
• the end of an included file.
• an include directive.
• 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 can be an absolute path, or just the base name. either way bestie, she'll figure it out 🧚

a filter can also be totally empty: []. such a filter has no effects. it's just standing there. existing. being decorative 🫶

✨ FILES ✨

• /etc/tunables.conf
• /etc/ld.so.cache — cached copy of tunables.

✨ EXAMPLES ✨

example configuration file, and yes we're looking at it together, come closer:

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 how the modifiers and filters are just vibing up there doing their little jobs? obsessed 😭✨

✨ SEE ALSO ✨

ld.so(8), ldconfig(8)

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and that's the whole thing, bestie 💖

little sign-off moment: this page comes to you from Linux man-pages 6.20, dated 2026-08-25. slay, and remember — always check the manpage for your glibc version, because the tunables list is a whole moving target 🌸💅🦋