man > kernel-command-line(7)

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

NAME
       kernel-command-line - Kernel command line parameters

SYNOPSIS
       /proc/cmdline

DESCRIPTION
       The kernel, the programs running in the initrd and in the host system 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 initrd, see dracut.cmdline(7), or the
       documentation of the specific initrd implementation of your installation.

CORE OS COMMAND LINE ARGUMENTS
       systemd.unit=, rd.systemd.unit=, systemd.dump_core, 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.log_ratelimit_kmsg, systemd.default_standard_output=,
       systemd.default_standard_error=, systemd.setenv=, systemd.machine_id=,
       systemd.set_credential=, systemd.set_credential_binary=, systemd.import_credentials=,
       systemd.reload_limit_interval_sec=, systemd.reload_limit_burst=
           Parameters understood by the system and service manager to control system behavior. For
           details, see systemd(1).

           Added in version 186.

       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.

           Added in version 215.

       systemd.run=, systemd.run_success_action=, systemd.run_failure_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.

           Added in version 240.

       systemd.early_core_pattern=
           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.

           Added in version 240.

       systemd.restore_state=
           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).

           Added in version 209.

       systemd.volatile=
           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).

           Added in version 233.

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

           Added in version 186.

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

           Added in version 205.

       -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 systemd(1).

           Added in version 186.

       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=,
       locale.LC_IDENTIFICATION=
           Parameters understood by the system and service manager to control locale and language
           settings. For details, see systemd(1).

           Added in version 186.

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

           Added in version 186.

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

           Added in version 186.

       systemd.journald.forward_to_syslog=, systemd.journald.forward_to_kmsg=,
       systemd.journald.forward_to_console=, systemd.journald.forward_to_wall=
           Parameters understood by the journal service. For details, see systemd-
           journald.service(8).

           Added in version 186.

       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).

           Added in version 186.

       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).

           Added in version 186.

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

           Added in version 186.

       luks=, rd.luks=, luks.crypttab=, rd.luks.crypttab=, luks.name=, rd.luks.name=, 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).

           Added in version 186.

       fstab=, rd.fstab=
           Configures the /etc/fstab logic at boot. For details, see systemd-fstab-generator(8).

           Added in version 186.

       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 systemd-
           fstab-generator(8).

           If root= is not set (or set to "gpt-auto") the automatic root partition discovery
           implemented by systemd-gpt-auto-generator(8) will be in effect. In this case rootfstype=,
           rootflags=, ro, rw will be interpreted by systemd-gpt-auto-generator.

           Added in version 215.

       mount.usr=, mount.usrfstype=, mount.usrflags=
           Configures the /usr file system (if required) and its file system type and mount options.
           For details, see systemd-fstab-generator(8).

           Added in version 235.

       veritytab=, rd.veritytab=, roothash=, systemd.verity=, rd.systemd.verity=,
       systemd.verity_root_data=, systemd.verity_root_hash=, systemd.verity.root_options=, usrhash=,
       systemd.verity_usr_data=, systemd.verity_usr_hash=, systemd.verity_usr_options=
           Configures the integrity protection root hash for the root and /usr file systems, and
           other related parameters. For details, see systemd-veritysetup-generator(8).

           Added in version 233.

       systemd.getty_auto=
           Configures whether the serial-getty@.service will run. For details, see systemd-getty-
           generator(8).

           Added in version 250.

       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).

           Added in version 215.

       systemd.image_policy=, rd.systemd.image_policy=
           When GPT-based partition auto-discovery is used, configures the image dissection policy
           string to apply, as per systemd.image-policy(7). For details see systemd-gpt-auto-
           generator(8).

           Added in version 254.

       systemd.default_timeout_start_sec=
           Overrides the default start job timeout DefaultTimeoutStartSec= at boot. For details, see
           systemd-system.conf(5).

           Added in version 230.

       systemd.default_device_timeout_sec=
           Overrides the default device timeout DefaultDeviceTimeoutSec= at boot. For details, see
           systemd-system.conf(5).

           Added in version 254.

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

           Added in version 236.

       systemd.watchdog_sec=
           Overrides the watchdog timeout settings otherwise configured with RuntimeWatchdog=,
           RebootWatchdog= and KExecWatchdogSec=. Takes a time value (if no unit is specified,
           seconds is the implicitly assumed time unit) or the special strings "off" or "default".
           For details, see systemd-system.conf(5).

           Added in version 250.

       systemd.watchdog_pre_sec=
           Overrides the watchdog pre-timeout settings otherwise configured with
           RuntimeWatchdogPreSec=. Takes a time value (if no unit is specified, seconds is the
           implicitly assumed time unit) or the special strings "off" or "default". For details, see
           systemd-system.conf(5).

           Added in version 251.

       systemd.watchdog_pretimeout_governor=
           Overrides the watchdog pre-timeout settings otherwise configured with
           RuntimeWatchdogPreGovernor=. Takes a string value. For details, see systemd-
           system.conf(5).

           Added in version 251.

       systemd.cpu_affinity=
           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.

           Added in version 245.

       modules_load=, rd.modules_load=
           Load a specific kernel module early at boot. For details, see systemd-modules-
           load.service(8).

           Added in version 187.

       nameserver=, domain=
           Configures DNS server information and search domains, see systemd-resolved.service(8) for
           details.

           Added in version 253.

       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).

           Added in version 217.

       systemd.firstboot=
           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.

           Added in version 233.

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

           Added in version 246.

       systemd.condition-first-boot=
           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).

           Added in version 246.

       systemd.clock-usec=
           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).

           Added in version 246.

       systemd.random-seed=
           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.

           Added in version 246.

       systemd.hostname=
           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.

           Added in version 246.

       systemd.tty.term.tty=, systemd.tty.rows.tty=, systemd.tty.columns.tty=
           These arguments allow configuring default values for $TERM, TTYRows=, and TTYColumns= for
           tty tty. Additionally, systemd.tty.term.console will configure the $TERM value used by
           systemd if not set explicitly using TERM on the kernel command line. The tty name should
           be specified without the /dev/ prefix (e.g.  "systemd.tty.rows.ttyS0=80").

           Added in version 254.

HISTORY
       systemd 252
           Kernel command-line arguments systemd.unified_cgroup_hierarchy and
           systemd.legacy_systemd_cgroup_controller were deprecated. Please switch to the unified
           cgroup hierarchy.

           Added in version 252.

SEE ALSO
       systemd(1), systemd-system.conf(5), bootparam(7), systemd.system-credentials(7) smbios-
       type-11(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-getty-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
        1. kernel-parameters.html
           https://docs.kernel.org/admin-guide/kernel-parameters.html

systemd 255                                                                   KERNEL-COMMAND-LINE(7)