kernel-command-line(7) — Linux manual page


KERNEL-COMMAND-LINE(7)     kernel-command-line    KERNEL-COMMAND-LINE(7)

NAME         top

       kernel-command-line - Kernel command line parameters

SYNOPSIS         top


DESCRIPTION         top

       The kernel, the initial RAM disk (initrd) and basic userspace
       functionality may be configured at boot via kernel command line
       arguments. In addition, various systemd tools look at the EFI
       variable "SystemdOptions" (if available). Both sources are
       combined, but the kernel command line has higher priority. Please
       note that the EFI variable is only used by systemd tools, and is
       ignored by the kernel and other user space tools, so it is not a
       replacement for the kernel command line.

       For command line parameters understood by the kernel, please see
       kernel-parameters.html[1] and bootparam(7).

       For command line parameters understood by the initial RAM disk,
       please see dracut.cmdline(7), or the documentation of the
       specific initrd implementation of your installation.


       systemd.unit=, rd.systemd.unit=, systemd.dump_core,
       systemd.early_core_pattern=, systemd.crash_chvt,
       systemd.crash_shell, systemd.crash_reboot, systemd.confirm_spawn,
       systemd.service_watchdogs, systemd.show_status,
       systemd.status_unit_format=, systemd.log_target=,
       systemd.log_level=, systemd.log_location=, systemd.log_color,
       systemd.default_standard_error=, systemd.setenv=,
       systemd.machine_id=, systemd.unified_cgroup_hierarchy,
           Parameters understood by the system and service manager to
           control system behavior. For details, see systemd(1).

       systemd.mask=, systemd.wants=, systemd.debug_shell
           Additional parameters understood by
           systemd-debug-generator(8), to mask or start specific units
           at boot, or invoke a debug shell on tty9., systemd.run_success_action=,
           Additional parameters understood by systemd-run-generator(8),
           to run a command line specified on the kernel command line as
           system service after booting up.

           During early boot, the generation of core dump files is
           disabled until a core dump handler (if any) takes over. This
           parameter allows specifying an absolute path where core dump
           files should be stored until a handler is installed. The path
           should be absolute and may contain specifiers, see core(5)
           for details.

           This parameter is understood by several system tools to
           control whether or not they should restore system state from
           the previous boot. For details, see
           systemd-backlight@.service(8) and systemd-rfkill.service(8).

           This parameter controls whether the system shall boot up in
           volatile mode. Takes a boolean argument, or the special value
           "state". If false (the default), normal boot mode is
           selected, the root directory and /var/ are mounted as
           specified on the kernel command line or /etc/fstab, or
           otherwise configured. If true, full state-less boot mode is
           selected. In this case the root directory is mounted as
           volatile memory file system ("tmpfs"), and only /usr/ is
           mounted from the file system configured as root device, in
           read-only mode. This enables fully state-less boots were the
           vendor-supplied OS is used as shipped, with only default
           configuration and no stored state in effect, as /etc/ and
           /var/ (as well as all other resources shipped in the root
           file system) are reset at boot and lost on shutdown. If this
           setting is set to "state" the root file system is mounted
           read-only, however /var/ is mounted as a volatile memory file
           system ("tmpfs"), so that the system boots up with the normal
           configuration applied, but all state reset at boot and lost
           at shutdown. If this setting is set to "overlay" the root
           file system is set up as "overlayfs" mount combining the
           read-only root directory with a writable "tmpfs", so that no
           modifications are made to disk, but the file system may be
           modified nonetheless with all changes being lost at reboot.
           For details, see systemd-volatile-root.service(8) and

           Parameter understood by both the kernel and the system and
           service manager to control console log verbosity. For
           details, see systemd(1).

           Parameter understood by both the kernel and the system and
           service manager to control console log verbosity. For
           details, see systemd(1).

       -b, rd.emergency, emergency, rd.rescue, rescue, single, s, S, 1,
       2, 3, 4, 5
           Parameters understood by the system and service manager, as
           compatibility and convenience options. For details, see

       locale.LANG=, locale.LANGUAGE=, locale.LC_CTYPE=,
       locale.LC_NUMERIC=, locale.LC_TIME=, locale.LC_COLLATE=,
       locale.LC_MONETARY=, locale.LC_MESSAGES=, locale.LC_PAPER=,
       locale.LC_NAME=, locale.LC_ADDRESS=, locale.LC_TELEPHONE=,
           Parameters understood by the system and service manager to
           control locale and language settings. For details, see

           Parameters understood by the file system checker services.
           For details, see systemd-fsck@.service(8).

           Parameter understood by the file quota checker service. For
           details, see systemd-quotacheck.service(8).

           Parameters understood by the journal service. For details,
           see systemd-journald.service(8).

       vconsole.keymap=, vconsole.keymap_toggle=, vconsole.font=,
       vconsole.font_map=, vconsole.font_unimap=
           Parameters understood by the virtual console setup logic. For
           details, see vconsole.conf(5).

       udev.log_level=, rd.udev.log_level=, udev.children_max=,
       rd.udev.children_max=, udev.exec_delay=, rd.udev.exec_delay=,
       udev.event_timeout=, rd.udev.event_timeout=,
       udev.timeout_signal=, rd.udev.timeout_signal=,
       udev.blockdev_read_only, rd.udev.blockdev_read_only,
       net.ifnames=, net.naming-scheme=
           Parameters understood by the device event managing daemon.
           For details, see systemd-udevd.service(8).

           May be used to disable the Plymouth boot splash. For details,
           see plymouth(8).

       luks=, rd.luks=, luks.crypttab=, rd.luks.crypttab=,,, luks.uuid=, rd.luks.uuid=, luks.options=,
       rd.luks.options=, luks.key=, rd.luks.key=
           Configures the LUKS full-disk encryption logic at boot. For
           details, see systemd-cryptsetup-generator(8).

       fstab=, rd.fstab=
           Configures the /etc/fstab logic at boot. For details, see

       root=, rootfstype=, rootflags=, ro, rw
           Configures the root file system and its file system type and
           mount options, as well as whether it shall be mounted
           read-only or read-write initially. For details, see

       mount.usr=, mount.usrfstype=, mount.usrflags=
           Configures the /usr file system (if required) and its file
           system type and mount options. For details, see

       veritytab=, rd.veritytab=, roothash=, systemd.verity=,
       rd.systemd.verity=, systemd.verity_root_data=,
       systemd.verity_root_hash=, systemd.verity.root_options=
           Configures the integrity protection root hash for the root
           file system, and other related parameters. For details, see

       systemd.gpt_auto=, rd.systemd.gpt_auto=
           Configures whether GPT based partition auto-discovery shall
           be attempted. For details, see systemd-gpt-auto-generator(8).

           Overwrites the default start job timeout
           DefaultTimeoutStartSec= at boot. For details, see

           Overwrites the watchdog device path WatchdogDevice=. For
           details, see systemd-system.conf(5).

           Overrides the CPU affinity mask for the service manager and
           the default for all child processes it forks. This takes
           precedence over CPUAffinity=, see systemd-system.conf(5) for

       modules_load=, rd.modules_load=
           Load a specific kernel module early at boot. For details, see

       resume=, resumeflags=
           Enables resume from hibernation using the specified device
           and mount options. All fstab(5)-like paths are supported. For
           details, see systemd-hibernate-resume-generator(8).

           Takes a boolean argument, defaults to on. If off,
           systemd-firstboot.service(8) will not query the user for
           basic system settings, even if the system boots up for the
           first time and the relevant settings are not initialized yet.
           Not to be confused with systemd.condition-first-boot= (see
           below), which overrides the result of the ConditionFirstBoot=
           unit file condition, and thus controls more than just
           systemd-firstboot.service behaviour.

           Takes a boolean argument. If specified, overrides the result
           of ConditionNeedsUpdate= unit condition checks. See
           systemd.unit(5) for details.

           Takes a boolean argument. If specified, overrides the result
           of ConditionFirstBoot= unit condition checks. See
           systemd.unit(5) for details. Not to be confused with
           systemd.firstboot= which only controls behaviour of the
           systemd-firstboot.service system service but has no effect on
           the condition check (see above).

           Takes a decimal, numeric timestamp in µs since January 1st
           1970, 00:00am, to set the system clock to. The system time is
           set to the specified timestamp early during boot. It is not
           propagated to the hardware clock (RTC).

           Takes a base64 encoded random seed value to credit with full
           entropy to the kernel's random pool during early service
           manager initialization. This option is useful in testing
           environments where delays due to random pool initialization
           in entropy starved virtual machines shall be avoided.

           Note that if this option is used the seed is accessible to
           unprivileged programs from /proc/cmdline. This option is
           hence a security risk when used outside of test systems,
           since the (possibly) only seed used for initialization of the
           kernel's entropy pool might be easily acquired by
           unprivileged programs.

           It is recommended to pass 512 bytes of randomized data (as
           that matches the Linux kernel pool size), which may be
           generated with a command like the following:

               dd if=/dev/urandom bs=512 count=1 status=none | base64 -w 0

           Again: do not use this option outside of testing
           environments, it's a security risk elsewhere, as secret key
           material derived from the entropy pool can possibly be
           reconstructed by unprivileged programs.

           Accepts a hostname to set during early boot. If specified
           takes precedence over what is set in /etc/hostname. Note that
           this does not bar later runtime changes to the hostname, it
           simply controls the initial hostname set during early boot.

SEE ALSO         top

       systemd(1), systemd-system.conf(5), bootparam(7),
       dracut.cmdline(7), systemd-debug-generator(8),
       systemd-fsck@.service(8), systemd-quotacheck.service(8),
       systemd-journald.service(8), systemd-vconsole-setup.service(8),
       systemd-udevd.service(8), plymouth(8),
       systemd-veritysetup-generator(8), systemd-fstab-generator(8),
       systemd-gpt-auto-generator(8), systemd-volatile-root.service(8),
       systemd-modules-load.service(8), systemd-backlight@.service(8),
       systemd-rfkill.service(8), systemd-hibernate-resume-generator(8),
       systemd-firstboot.service(8), bootctl(1)

NOTES         top

        1. kernel-parameters.html

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-27.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 249                                       KERNEL-COMMAND-LINE(7)

Pages that refer to this page: systemd(1)systemd-nspawn(1)hostname(5)systemd.exec(5)systemd-debug-generator(8)systemd-fstab-generator(8)systemd-hibernate-resume-generator(8)systemd-run-generator(8)systemd-volatile-root.service(8)