Documentation for /proc/sys

Copyright (c) 1998, 1999, Rik van Riel <>

'Why', I hear you ask, 'would anyone even _want_ documentation for them sysctl files? If anybody really needs it, it's all in the source...'

Well, this documentation is written because some people either don't know they need to tweak something, or because they don't have the time or knowledge to read the source code.

Furthermore, the programmers who built sysctl have built it to be actually used, not just for the fun of programming it :-)

Legal blurb:

As usual, there are two main things to consider:

  1. you get what you pay for

  2. it's free

The consequences are that I won't guarantee the correctness of this document, and if you come to me complaining about how you screwed up your system because of wrong documentation, I won't feel sorry for you. I might even laugh at you...

But of course, if you _do_ manage to screw up your system using only the sysctl options used in this file, I'd like to hear of it. Not only to have a great laugh, but also to make sure that you're the last RTFMing person to screw up.

In short, e-mail your suggestions, corrections and / or horror stories to: <>

Rik van Riel.


Sysctl is a means of configuring certain aspects of the kernel at run-time, and the /proc/sys/ directory is there so that you don't even need special tools to do it! In fact, there are only four things needed to use these config facilities:

  • a running Linux system

  • root access

  • common sense (this is especially hard to come by these days)

  • knowledge of what all those values mean

As a quick 'ls /proc/sys' will show, the directory consists of several (arch-dependent?) subdirs. Each subdir is mainly about one part of the kernel, so you can do configuration on a piece by piece basis, or just some 'thematic frobbing'.

This documentation is about:


execution domains & personalities




device specific information (eg dev/cdrom/info)


specific filesystems filehandle, inode, dentry and quota tuning binfmt_misc <Kernel Support for miscellaneous Binary Formats (binfmt_misc)>


global kernel info / tuning miscellaneous stuff


networking stuff, for documentation look in: <Documentation/networking/>




SUN Remote Procedure Call (NFS)


memory management tuning buffer and cache management


Per user per user namespace limits

These are the subdirs I have on my system. There might be more or other subdirs in another setup. If you see another dir, I'd really like to hear about it :-)