SYSCTL.CONF(5)

💖 SYSCTL.CONF 💖

okay bestie, so this is a file formats manual page — the SYSCTL.CONF(5) one — and it's literally the blueprint for how you tell your Linux kernel what it should be doing. no cap.

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✨ NAME ✨

sysctl.conf — Linux kernel configuration parameters 🎀

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🌸 DESCRIPTION 🌸

sysctl.conf is a whole set of configuration files, and they contain Linux kernel configuration parameters — the ones that get read and set by sysctl(8). it's giving "kernel settings, but make it a text file". 💅

This man page is specifically about the configuration files for procps sysctl. So if you're out here using systemd-sysctl(8) instead, go read sysctl.d(5) — and heads up, queen, it won't use the file /etc/sysctl.conf. different implementation, different rules. 🦋

📝 Configuration Format

Each line of a file that procps sysctl reads describes a kernel parameter, and it looks like this:

token = value

and no — you do not need quotation marks around value, even when value is a whole list of items. the file just gets it. iconic. ✨

Blank lines? ignored. Lines that start with # or ;? also ignored. those are your comment lines, bestie. 💜

and here's a lil trick: if a line begins with a single -, then a failing attempt to set the value is ignored. so it's like "try it, but don't be dramatic if it doesn't work". 🙈

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🗂️ FILES 🗂️

procps sysctl, when you run it with the --system option, reads files from these directories — in this exact order, no skipping, no shuffling:

/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf

and finally, procps sysctl reads /etc/sysctl.conf. 👑

⚠️ that last file is not used by systemd-sysctl — which means some kernel parameters are just not set, depending on which implementation of sysctl you have installed. so like, know which one you're running, fr fr. 😭

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💀 BUGS 💀

The maximum supported length of value is 4096 characters, because of a limitation on /proc entry length in the Linux kernel. so don't go writing a whole novel in there, bestie. 4096 and that's it. periodt.

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🌈 EXAMPLES 🌈

#
#
kernel.domainname = example.com
; A value containing a space is written to the sysctl.
kernel.modprobe = /sbin/mod probe
# A list of items for the value
net.ipv4.ip_local_reserved_ports=8080,9148

look at that — comments, a value with a space in it, and a whole comma-separated list. all three vibes, one file. ate. 🔥

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👀 SEE ALSO 👀

sysctl.d(5), sysctl(8), systemd-sysctl(8)

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and that's the whole page, bestie 🫶 this was procps-ng, dated 2025-05-29, and you're officially a SYSCTL.CONF(5) girlie now. go set some kernel parameters. slay. 💖✨🎀