systemd-boot(7) — Linux manual page


SYSTEMD-BOOT(7)               systemd-boot               SYSTEMD-BOOT(7)

NAME         top

       systemd-boot, sd-boot - A simple UEFI boot manager

DESCRIPTION         top

       systemd-boot (short: sd-boot) is a simple UEFI boot manager. It
       provides a textual menu to select the entry to boot and an editor
       for the kernel command line.  systemd-boot supports systems with
       UEFI firmware only.

       systemd-boot loads boot entry information from the EFI system
       partition (ESP), usually mounted at /efi/, /boot/, or /boot/efi/
       during OS runtime, as well as from the Extended Boot Loader
       partition (XBOOTLDR) if it exists (usually mounted to /boot/).
       Configuration file fragments, kernels, initrds and other EFI
       images to boot generally need to reside on the ESP or the
       Extended Boot Loader partition. Linux kernels must be built with
       CONFIG_EFI_STUB to be able to be directly executed as an EFI
       image. During boot systemd-boot automatically assembles a list of
       boot entries from the following sources:

       •   Boot entries defined with Boot Loader Specification[1] Type
           #1 description files located in /loader/entries/ on the ESP
           and the Extended Boot Loader Partition. These usually
           describe Linux kernel images with associated initrd images,
           but alternatively may also describe other arbitrary EFI

       •   Unified kernel images, Boot Loader Specification[1] Type #2,
           which are executable EFI binaries in /EFI/Linux/ on the ESP
           and the Extended Boot Loader Partition.

       •   The Microsoft Windows EFI boot manager, if installed.

       •   The Apple macOS boot manager, if installed.

       •   The EFI Shell binary, if installed.

       •   A "Reboot Into Firmware Interface option", if supported by
           the UEFI firmware.

       •   Secure Boot variables enrollment if the UEFI firmware is in
           setup-mode and files are provided on the ESP.

       systemd-boot supports the following features:

       •   Basic boot manager configuration changes (such as timeout
           configuration, default boot entry selection, ...) may be made
           directly from the boot loader UI at boot-time, as well as
           during system runtime with EFI variables.

       •   The boot manager integrates with the systemctl command to
           implement features such as systemctl reboot
           --boot-loader-entry=...  (for rebooting into a specific boot
           menu entry, i.e. "reboot into Windows") and systemctl reboot
           --boot-loader-menu=...  (for rebooting into the boot loader
           menu), by implementing the Boot Loader Interface[2]. See
           systemctl(1) for details.

       •   An EFI variable set by the boot loader informs the OS about
           the EFI System Partition used during boot. This is then used
           to automatically mount the correct EFI System Partition to
           /efi/ or /boot/ during OS runtime. See
           systemd-gpt-auto-generator(8) for details.

       •   The boot manager provides information about the boot time
           spent in UEFI firmware using the Boot Loader Interface[2].
           This information can be displayed using systemd-analyze(1).

       •   The boot manager implements boot counting and automatic
           fallback to older, working boot entries on failure. See
           Automatic Boot Assessment[3].

       •   The boot manager optionally reads a random seed from the ESP
           partition, combines it with a 'system token' stored in a
           persistent EFI variable and derives a random seed to use by
           the OS as entropy pool initialization, providing a full
           entropy pool during early boot.

       •   The boot manager allows for Secure Boot variables to be
           enrolled if the UEFI firmware is in setup-mode. Additionally,
           variables can be automatically enrolled if configured.

       bootctl(1) may be used from a running system to locate the ESP
       and the Extended Boot Loader Partition, list available entries,
       and install systemd-boot itself.

       kernel-install(8) may be used to copy kernel images onto the ESP
       or the Extended Boot Loader Partition and to generate description
       files compliant with the Boot Loader Specification.

       systemd-stub(7) may be used as UEFI boot stub for executed
       kernels, which is useful to show graphical boot splashes before
       transitioning into the Linux world. It is also capable of
       automatically picking up auxiliary credential files (for boot
       parameterization) and system extension images, as companion files
       to the booted kernel images.

KEY BINDINGS         top

       The following keys may be used in the boot menu:

       ↑ (Up), ↓ (Down), j, k, PageUp, PageDown, Home, End
           Navigate up/down in the entry list

           Added in version 239.

       ↵ (Enter), → (Right)
           Boot selected entry

           Added in version 239.

           Make selected entry the default

           Added in version 239.

           Edit the kernel command line for selected entry

           Added in version 239.

       +, t
           Increase the timeout before default entry is booted

           Added in version 239.

       -, T
           Decrease the timeout

           Added in version 239.

           Change screen resolution, skipping any unsupported modes.

           Added in version 250.

           Reset screen resolution to firmware or configuration file

           Added in version 250.

           Print status

           Added in version 250.

       h, ?, F1
           Show a help screen

           Added in version 239.

           Reboot into firmware interface.

           For compatibility with the keybindings of several firmware
           implementations this operation may also be reached with F2,
           F10, Del and Esc.

           Added in version 250.

           Power off the system.

           Added in version 255.

           Reboot the system.

           Added in version 255.

       The following keys may be pressed during bootup or in the boot
       menu to directly boot a specific entry:


           Added in version 239.


           Added in version 239.


           Added in version 239.

           EFI shell

           Added in version 239.

       1, 2, 3, 4, 5, 6, 7, 8, 9
           Boot entry number 1 ... 9

           Added in version 239.

       The boot menu is shown when a non-zero menu timeout has been
       configured. If the menu timeout has been set to zero, it is
       sufficient to press any key — before the boot loader initializes
       — to bring up the boot menu, except for the keys listed
       immediately above as they directly boot into the selected boot
       menu item. Note that depending on the firmware implementation the
       time window where key presses are accepted before the boot loader
       initializes might be short. If the window is missed, reboot and
       try again, possibly pressing a suitable key (e.g. the space bar)
       continuously; on most systems it should be possible to hit the
       time window after a few attempts. To avoid this problem, consider
       setting a non-zero timeout, thus showing the boot menu
       unconditionally. Some desktop environments might offer an option
       to directly boot into the boot menu, to avoid the problem
       altogether. Alternatively, use the command line systemctl reboot
       --boot-loader-menu=0 from the shell.

       In the editor, most keys simply insert themselves, but the
       following keys may be used to perform additional actions:

       ← (Left), → (Right), Home, End
           Navigate left/right

           Added in version 239.

       Esc, Ctrl+c
           Abort the edit and quit the editor

           Added in version 239.

           Clear the command line forwards

           Added in version 239.

       Ctrl+w, Alt+Backspace
           Delete word backwards

           Added in version 239.

       Ctrl+Del, Alt+d
           Delete word forwards

           Added in version 239.

       ↵ (Enter)
           Boot entry with the edited command line

           Added in version 239.

       Note that unless configured otherwise in the UEFI firmware,
       systemd-boot will use the US keyboard layout, so key labels might
       not match for keys like +/-.

FILES         top

       The files systemd-boot processes generally reside on the UEFI ESP
       which is usually mounted to /efi/, /boot/ or /boot/efi/ during OS
       runtime. It also processes files on the Extended Boot Loader
       partition which is typically mounted to /boot/, if it exists.

       systemd-boot reads runtime configuration such as the boot timeout
       and default entry from /loader/loader.conf on the ESP (in
       combination with data read from EFI variables). See

       Boot entry description files following the Boot Loader
       Specification[1] are read from /loader/entries/ on the ESP and
       the Extended Boot Loader partition.

       Unified kernel boot entries following the Boot Loader
       Specification[1] are read from /EFI/Linux/ on the ESP and the
       Extended Boot Loader partition.

       Optionally, a random seed for early boot entropy pool
       provisioning is stored in /loader/random-seed in the ESP.

       During initialization, sd-boot automatically loads all driver
       files placed in the /EFI/systemd/drivers/ directory of the ESP.
       The files placed there must have an extension of the EFI
       architecture ID followed by .efi (e.g. for x86-64 this means a
       suffix of x64.efi). This may be used to automatically load file
       system drivers and similar, to extend the native firmware

       Enrollment of Secure Boot variables can be performed manually or
       automatically if files are available under
       /loader/keys/NAME/{db,dbx,KEK,PK}.auth, NAME being the display
       name for the set of variables in the menu. If one of the sets is
       named auto then it might be enrolled automatically depending on
       whether "secure-boot-enroll" is set to force or not.

EFI VARIABLES         top

       The following EFI variables are defined, set and read by
       systemd-boot, under the vendor UUID
       "4a67b082-0a4c-41cf-b6c7-440b29bb8c4f", for communication between
       the boot loader and the OS:

           If boot counting is enabled, contains the path to the file in
           whose name the boot counters are encoded. Set by the boot
           loader.  systemd-bless-boot.service(8) uses this information
           to mark a boot as successful as determined by the successful
           activation of the target unit.

           Added in version 240.

       LoaderConfigTimeout, LoaderConfigTimeoutOneShot
           The menu timeout in seconds. Read by the boot loader.
           LoaderConfigTimeout is maintained persistently, while
           LoaderConfigTimeoutOneShot is a one-time override which is
           read once (in which case it takes precedence over
           LoaderConfigTimeout) and then removed.  LoaderConfigTimeout
           may be manipulated with the t/T keys, see above.

           Added in version 240.

           The numerical menu console mode. Read by the boot loader.
           LoaderConfigConsoleMode is maintained persistently.
           LoaderConfigConsoleMode may be manipulated with the r/R keys,
           see above.

           Added in version 250.

           Contains the partition UUID of the EFI System Partition the
           boot loader was run from. Set by the boot loader.
           systemd-gpt-auto-generator(8) uses this information to
           automatically find the disk booted from, in order to discover
           various other partitions on the same disk automatically.

           Added in version 240.

           A list of the identifiers of all discovered boot loader
           entries. Set by the boot loader.

           Added in version 240.

       LoaderEntryDefault, LoaderEntryOneShot
           The identifier of the default boot loader entry. Set
           primarily by the OS and read by the boot loader.
           LoaderEntryOneShot sets the default entry for the next boot
           only, while LoaderEntryDefault sets it persistently for all
           future boots.  bootctl(1)'s set-default and set-oneshot
           commands make use of these variables. The boot loader
           modifies LoaderEntryDefault on request, when the d key is
           used, see above.

           Added in version 240.

           The identifier of the boot loader entry last attempted. Set
           and read by the boot loader, only when /loader/loader.conf
           has default set to "@saved". See loader.conf(5).

           The boot loader will ensure LoaderEntryLastBooted is up-to
           date for every boot, updating it as needed and will omit
           changing it all together when LoaderEntryOneShot is set.

           The boot loader reads the variable, which takes higher
           priority than LoaderEntryDefault. The variable is ignored
           when LoaderEntryOneShot is set.

           LoaderEntryLastBooted cannot be used as indication that the
           last boot was successful or not.

           Added in version 250.

           The identifier of the boot loader entry currently being
           booted. Set by the boot loader.

           Added in version 240.

           A set of flags indicating the features the boot loader
           supports. Set by the boot loader. Use bootctl(1) to view this

           Added in version 240.

       LoaderFirmwareInfo, LoaderFirmwareType
           Brief firmware information. Set by the boot loader. Use
           bootctl(1) to view this data.

           Added in version 240.

           The path of executable of the boot loader used for the
           current boot, relative to the EFI System Partition's root
           directory. Set by the boot loader. Use bootctl(1) to view
           this data.

           Added in version 240.

           Brief information about the boot loader. Set by the boot
           loader. Use bootctl(1) to view this data.

           Added in version 240.

       LoaderTimeExecUSec, LoaderTimeInitUSec, LoaderTimeMenuUsec
           Information about the time spent in various parts of the boot
           loader. Set by the boot loader. Use systemd-analyze(1) to
           view this data.

           Added in version 240.

           A binary random data field, that is used for generating the
           random seed to pass to the OS (see above). Note that this
           random data is generally only generated once, during OS
           installation, and is then never updated again.

           Added in version 243.

       Many of these variables are defined by the Boot Loader

SMBIOS TYPE 11 STRINGS         top

       systemd-boot can be configured using SMBIOS Type 11 strings.
       Applicable strings consist of a name, followed by "=", followed
       by the value. Unless systemd-boot detects it is running inside a
       confidential computing environment, systemd-boot will search the
       table for a string with a specific name, and if found, use its
       value. The following strings are read:

           If set, the value of this string is added to the list of
           kernel command line arguments for Boot Loader Specification
           Type 1 entries that are measured in PCR12 and passed to the

           Added in version 256.

BOOT COUNTING         top

       systemd-boot implements a simple boot counting mechanism on top
       of the Boot Loader Specification[1], for automatic and unattended
       fallback to older kernel versions/boot loader entries when a
       specific entry continuously fails. Any boot loader entry file and
       unified kernel image file that contains a "+" followed by one or
       two numbers (if two they need to be separated by a "-"), before
       the .conf or .efi suffix is subject to boot counting: the first
       of the two numbers ('tries left') is decreased by one on every
       boot attempt, the second of the two numbers ('tries done') is
       increased by one (if 'tries done' is absent it is considered
       equivalent to 0). Depending on the current value of these two
       counters the boot entry is considered to be in one of three

        1. If the 'tries left' counter of an entry is greater than zero
           the entry is considered to be in 'indeterminate' state. This
           means the entry has not completed booting successfully yet,
           but also hasn't been determined not to work.

        2. If the 'tries left' counter of an entry is zero it is
           considered to be in 'bad' state. This means no further
           attempts to boot this item will be made (that is, unless all
           other boot entries are also in 'bad' state), as all attempts
           to boot this entry have not completed successfully.

        3. If the 'tries left' and 'tries done' counters of an entry are
           absent it is considered to be in 'good' state. This means
           further boot counting for the entry is turned off, as it
           successfully booted at least once. The
           systemd-bless-boot.service(8) service moves the currently
           booted entry from 'indeterminate' into 'good' state when a
           boot attempt completed successfully.

       Generally, when new entries are added to the boot loader, they
       first start out in 'indeterminate' state, i.e. with a 'tries
       left' counter greater than zero. The boot entry remains in this
       state until either it managed to complete a full boot
       successfully at least once (in which case it will be in 'good'
       state) — or the 'tries left' counter reaches zero (in which case
       it will be in 'bad' state).

       Example: let's say a boot loader entry file foo.conf is set up
       for 3 boot tries. The installer will hence create it under the
       name foo+3.conf. On first boot, the boot loader will rename it to
       foo+2-1.conf. If that boot does not complete successfully, the
       boot loader will rename it to foo+1-2.conf on the following boot.
       If that fails too, it will finally be renamed foo+0-3.conf by the
       boot loader on next boot, after which it will be considered
       'bad'. If the boot succeeds however the entry file will be
       renamed to foo.conf by the OS, so that it is considered 'good'
       from then on.

       The boot menu takes the 'tries left' counter into account when
       sorting the menu entries: entries in 'bad' state are ordered at
       the beginning of the list, and entries in 'good' or
       'indeterminate' at the end. The user can freely choose to boot
       any entry of the menu, including those already marked 'bad'. If
       the menu entry to boot is automatically determined, this means
       that 'good' or 'indeterminate' entries are generally preferred
       (as the bottom item of the menu is the one booted by default),
       and 'bad' entries will only be considered if there are no 'good'
       or 'indeterminate' entries left.

       The kernel-install(8) kernel install framework optionally sets
       the initial 'tries left' counter to the value specified in
       /etc/kernel/tries when a boot loader entry is first created.


       When using qemu with OVMF (UEFI Firmware for virtual machines)
       the -kernel switch works not only for linux kernels, but for any
       EFI binary, including sd-boot and unified linux kernels. Example
       command line for loading systemd-boot on x64:

       qemu-system-x86_64 [ ... ] -kernel

       systemd-boot will detect that it was started directly instead of
       being loaded from ESP and will search for the ESP in that case,
       taking into account boot order information from the hypervisor
       (if available).

SEE ALSO         top

       bootctl(1), loader.conf(5), systemd-bless-boot.service(8),
       systemd-boot-random-seed.service(8), kernel-install(8),
       systemd-stub(7), Boot Loader Specification[1], Boot Loader
       Interface[2], TPM2 PCR Measurements Made by systemd[4]

NOTES         top

        1. Boot Loader Specification

        2. Boot Loader Interface

        3. Automatic Boot Assessment

        4. TPM2 PCR Measurements Made by systemd

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 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  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 257~devel                                        SYSTEMD-BOOT(7)

Pages that refer to this page: bootctl(1)systemd-cryptenroll(1)ukify(1)loader.conf(5)org.freedesktop.login1(5)bootup(7)systemd.directives(7)systemd.index(7)systemd-stub(7)kernel-install(8)systemd-bless-boot-generator(8)systemd-bless-boot.service(8)systemd-boot-random-seed.service(8)systemd-random-seed.service(8)