06-B.7: Kernel Modules - Kernel Parameters
- Page ID
- 32791
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Kernel Parameters
The /proc/sys directory contains a lot of useful and interesting files and directories. Many kernel settings can be manipulated by writing to files in the proc filesystem. A lot of important information can be retrieved from these files. This is especially useful when you are troubleshooting or fine tuning your Linux system.
The /proc/sys directory is divided into subdirectories:
| Subdirectory | What it is |
|---|---|
| abi/ | Execution domains & personalities |
| debug/ | <empty> |
| dev/ | Device specific information (eg dev/cdrom/info) |
| fs/ | Specific filesystems filehandle, inode, dentry and quota tuning binfmt_misc <Documentation/admin-guide/binfmt-misc.rst> |
| kernel/ | Global kernel info / tuning miscellaneous stuff |
| net/ | Networking stuff, for documentation look in: <Documentation/networking/> |
| vm/ | Memory management tuning buffer and cache management |
| user/ | Per user per user namespace limits |
The sysctl Command
The sysctl is a software utility that reads and modifies the attributes of the system kernel such as its version number, maximum limits, and security settings. It is available both as a system call for compiled programs, and an administrator command for interactive use and scripting.
Syntax:
sysctl [ OPTIONS ]
| Options | Options Meaning |
|---|---|
| -a, --all | Display all values currently available. |
| -e, --ignore | Use this option to ignore errors about unknown keys. |
| -p [FILENAME}, --load[=FILENAME] | Load in sysctl settings from the file specified or /etc/sysctl.conf if none given. |
| -r, --pattern pattern | Only apply settings that match pattern. |
| -w, --write | Use this option when you want to change a sysctl setting. |
To see what the attributes look like use the -a option and the command will output ALL of the currently configured parameters. There are many more than the few shown in the example - the system that this was run on had a total of 936 parameters.
pbmac@pbmac-server $ sysctl -a
abi.vsyscall32 = 1
debug.exception-trace = 1
debug.kprobes-optimization = 1
dev.cdrom.autoclose = 1
dev.cdrom.autoeject = 0
dev.cdrom.check_media = 0
dev.cdrom.debug = 0
dev.cdrom.info = CD-ROM information, Id: cdrom.c 3.20 2003/12/17
The sysctl.conf File
The sysctl preload/configuration file can be created at /etc/sysctl.d/99-sysctl.conf. Current Linux distributions no longer maintain the /etc/sysctl.conf file. All of the configurations are contained in individual files in the /etc/sysctl.d/ directory.
Settings can be changed through file manipulation or using the sysctl utility. ForThis will change the current value of the parameter until the system is rebooted.
pbmac@pbmac-server $ sysctl kernel.sysrq=1
To preserve changes between reboots, add or modify the appropriate lines in /etc/sysctl.d/99-sysctl.conf or create an applicable parameter file in /etc/sysctl.d/.
Adapted from:
"Sysctl" by Multiple contributors, ArchWiki is licensed under CC BY-SA 4.0