простой менеджер загрузки UEFI (A simple UEFI boot manager)
Имя (Name)
systemd-boot, sd-boot - A simple UEFI boot manager
Описание (Description)
systemd-boot (short: sd-boot) is a simple UEFI boot manager. It
provides a graphical 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 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
• Unified kernel images following the Boot Loader
Specification
• The Microsoft Windows EFI boot manager, if installed
• The Apple macOS boot manager, if installed
• The EFI Shell binary, if installed
• A reboot into the UEFI firmware setup option, if supported by
the firmware
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
• 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
• The boot manager implements boot counting and automatic
fallback to older, working boot entries on failure. See
Automatic Boot Assessment
• 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.
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.
Ключи (Keys)
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
↵ (Enter), → (Right)
Boot selected entry
d
Make selected entry the default
e
Edit the kernel command line for selected entry
+, t
Increase the timeout before default entry is booted
-, T
Decrease the timeout
p
Print status
h, ?, F1
Show a help screen
The following keys may be pressed during bootup or in the boot
menu to directly boot a specific entry:
l
Linux
w
Windows
a
macOS
s
EFI shell
1, 2, 3, 4, 5, 6, 7, 8, 9
Boot entry number 1 ... 9
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
Esc
Abort the edit and quit the editor
Ctrl+k
Clear the command line
Ctrl+w, Alt+Backspace
Delete word backwards
Alt+d
Delete word forwards
↵ (Enter)
Boot entry with the edited command line
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 +/-.
Файлы (Files)
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
loader.conf(5). Boot entry description files following the Boot
Loader SpecificationBoot Loader Specification
Переменные EFI (EFI variables)
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 OS and the boot loader:
LoaderBootCountPath
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 boot-complete.target target unit.
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.
LoaderDevicePartUUID
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.
LoaderEntries
A list of the identifiers of all discovered boot loader
entries. Set by the boot loader.
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.
LoaderEntrySelected
The identifier of the boot loader entry currently being
booted. Set by the boot loader.
LoaderFeatures
A set of flags indicating the features the boot loader
supports. Set by the boot loader. Use bootctl(1) to view this
data.
LoaderFirmwareInfo, LoaderFirmwareType
Brief firmware information. Set by the boot loader. Use
bootctl(1) to view this data.
LoaderImageIdentifier
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.
LoaderInfo
Brief information about the boot loader. Set by the boot
loader. Use bootctl(1) to view this data.
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.
LoaderRandomSeed
A binary random seed systemd-boot may optionally pass to the
OS. This is a volatile EFI variable that is hashed at boot
from the combination of a random seed stored in the ESP (in
/loader/random-seed) and a "system token" persistently stored
in the EFI variable LoaderSystemToken (see below). During
early OS boot the system manager reads this variable and
passes it to the OS kernel's random pool, crediting the full
entropy it contains. This is an efficient way to ensure the
system starts up with a fully initialized kernel random pool
— as early as the initial RAM disk phase. systemd-boot reads
the random seed from the ESP, combines it with the "system
token", and both derives a new random seed to update in-place
the seed stored in the ESP, and the random seed to pass to
the OS from it via SHA256 hashing in counter mode. This
ensures that different physical systems that boot the same
"golden" OS image — i.e. containing the same random seed file
in the ESP — will still pass a different random seed to the
OS. It is made sure the random seed stored in the ESP is
fully overwritten before the OS is booted, to ensure
different random seed data is used between subsequent boots.
See Random Seeds
LoaderSystemToken
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.
Many of these variables are defined by the Boot Loader
Interface
BOOT COUNTING
systemd-boot implements a simple boot counting mechanism on top
of the Boot Loader Specification
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.
Смотри также (See also)
bootctl(1), loader.conf(5), systemd-bless-boot.service(8),
systemd-boot-system-token.service(8), kernel-install(8), Boot
Loader SpecificationBoot Loader Interface
Примечание (Note)
1. Boot Loader Specification
https://systemd.io/BOOT_LOADER_SPECIFICATION
2. Boot Loader Interface
https://systemd.io/BOOT_LOADER_INTERFACE
3. Automatic Boot Assessment
https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT
4. Random Seeds
https://systemd.io/RANDOM_SEEDS
