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_output=, systemd.default_standard_error=,
       systemd.setenv=, systemd.machine_id=,
           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

           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 systemd-fstab-generator(8).

           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=, locale.LC_MEASUREMENT=,
           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

       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

       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

       roothash=, systemd.verity=, rd.systemd.verity=,
       systemd.verity_root_data=, systemd.verity_root_hash=
           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 systemd-system.conf(5).

           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 details.

       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-cryptsetup-generator(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 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-11-01.)  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 im‐
       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to

systemd 247                                           KERNEL-COMMAND-LINE(7)

Pages that refer to this page: init(1)systemd(1)systemd-nspawn(1)systemd.exec(5)30-systemd-environment-d-generator(7)systemd.directives(7)systemd.index(7)systemd-debug-generator(8)systemd-fstab-generator(8)systemd-hibernate-resume-generator(8)systemd-run-generator(8)systemd-volatile-root(8)systemd-volatile-root.service(8)