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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 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.
CORE OS COMMAND LINE ARGUMENTS
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=, systemd.unified_cgroup_hierarchy,
systemd.legacy_systemd_cgroup_controller
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=, 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.
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.
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).
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).
quiet
Parameter understood by both the kernel and the system and service manager to control
console log verbosity. For details, see systemd(1).
debug
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 systemd(1).
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).
fsck.mode=, fsck.repair=
Parameters understood by the file system checker services. For details, see systemd-
fsck@.service(8).
quotacheck.mode=
Parameter understood by the file quota checker service. For details, see systemd-
quotacheck.service(8).
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).
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).
plymouth.enable=
May be used to disable the Plymouth boot splash. For details, see plymouth(8).
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).
fstab=, rd.fstab=
Configures the /etc/fstab logic at boot. For details, see systemd-fstab-generator(8).
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).
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).
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-veritysetup-generator(8).
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).
systemd.default_timeout_start_sec=
Overwrites the default start job timeout DefaultTimeoutStartSec= at boot. For details,
see systemd-system.conf(5).
systemd.watchdog_device=
Overwrites the watchdog device path WatchdogDevice=. For details, see systemd-
system.conf(5).
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.
modules_load=, rd.modules_load=
Load a specific kernel module early at boot. For details, see systemd-modules-
load.service(8).
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).
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.
systemd.condition-needs-update=
Takes a boolean argument. If specified, overrides the result of ConditionNeedsUpdate=
unit condition checks. See systemd.unit(5) for details.
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).
systemd.clock-usec=
Takes a decimal, numeric timestamp in <micro>s 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).
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.
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.
SEE ALSO
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
1. kernel-parameters.html
https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
systemd 249 KERNEL-COMMAND-LINE(7)
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