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06-B.7: Kernel Modules - Kernel Parameters

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    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:

    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.


    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 = 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

    06-B.7: Kernel Modules - Kernel Parameters is shared under a CC BY-NC license and was authored, remixed, and/or curated by LibreTexts.

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