460 lines
14 KiB
Plaintext
460 lines
14 KiB
Plaintext
15 GRUB environment variables
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*****************************
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GRUB supports environment variables which are rather like those offered
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by all Unix-like systems. Environment variables have a name, which is
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unique and is usually a short identifier, and a value, which is an
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arbitrary string of characters. They may be set (*note set::), unset
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(*note unset::), or looked up (*note Shell-like scripting::) by name.
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A number of environment variables have special meanings to various
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parts of GRUB. Others may be used freely in GRUB configuration files.
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15.1 Special environment variables
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==================================
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These variables have special meaning to GRUB.
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15.1.1 biosnum
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--------------
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When chain-loading another boot loader (*note Chain-loading::), GRUB may
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need to know what BIOS drive number corresponds to the root device
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(*note root::) so that it can set up registers properly. If the BIOSNUM
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variable is set, it overrides GRUB's own means of guessing this.
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For an alternative approach which also changes BIOS drive mappings
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for the chain-loaded system, *note drivemap::.
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15.1.2 check_signatures
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-----------------------
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This variable controls whether GRUB enforces digital signature
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validation on loaded files. *Note Using digital signatures::.
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15.1.3 chosen
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-------------
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When executing a menu entry, GRUB sets the CHOSEN variable to the title
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of the entry being executed.
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If the menu entry is in one or more submenus, then CHOSEN is set to
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the titles of each of the submenus starting from the top level followed
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by the title of the menu entry itself, separated by '>'.
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15.1.4 cmdpath
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--------------
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The location from which 'core.img' was loaded as an absolute directory
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name (*note File name syntax::). This is set by GRUB at startup based
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on information returned by platform firmware. Not every platform
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provides this information and some may return only device without path
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name.
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15.1.5 color_highlight
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----------------------
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This variable contains the "highlight" foreground and background
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terminal colors, separated by a slash ('/'). Setting this variable
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changes those colors. For the available color names, *note
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color_normal::.
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The default is 'black/light-gray'.
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15.1.6 color_normal
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-------------------
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This variable contains the "normal" foreground and background terminal
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colors, separated by a slash ('/'). Setting this variable changes those
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colors. Each color must be a name from the following list:
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* black
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* blue
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* green
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* cyan
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* red
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* magenta
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* brown
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* light-gray
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* dark-gray
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* light-blue
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* light-green
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* light-cyan
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* light-red
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* light-magenta
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* yellow
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* white
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The default is 'light-gray/black'.
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The color support support varies from terminal to terminal.
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'morse' has no color support at all.
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'mda_text' color support is limited to highlighting by black/white
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reversal.
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'console' on ARC, EMU and IEEE1275, 'serial_*' and 'spkmodem' are
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governed by terminfo and support only 8 colors if in modes 'vt100-color'
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(default for console on emu), 'arc' (default for console on ARC),
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'ieee1275' (default for console on IEEE1275). When in mode 'vt100' then
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the color support is limited to highlighting by black/white reversal.
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When in mode 'dumb' there is no color support.
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When console supports no colors this setting is ignored. When
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console supports 8 colors, then the colors from the second half of the
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previous list are mapped to the matching colors of first half.
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'console' on EFI and BIOS and 'vga_text' support all 16 colors.
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'gfxterm' supports all 16 colors and would be theoretically
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extendable to support whole rgb24 palette but currently there is no
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compelling reason to go beyond the current 16 colors.
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15.1.7 config_directory
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-----------------------
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This variable is automatically set by GRUB to the directory part of
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current configuration file name (*note config_file::).
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15.1.8 config_file
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------------------
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This variable is automatically set by GRUB to the name of configuration
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file that is being processed by commands 'configfile' (*note
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configfile::) or 'normal' (*note normal::). It is restored to the
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previous value when command completes.
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15.1.9 debug
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------------
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This variable may be set to enable debugging output from various
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components of GRUB. The value is a list of debug facility names
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separated by whitespace or ',', or 'all' to enable all available
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debugging output. The facility names are the first argument to
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grub_dprintf. Consult source for more details.
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15.1.10 default
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---------------
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If this variable is set, it identifies a menu entry that should be
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selected by default, possibly after a timeout (*note timeout::). The
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entry may be identified by number (starting from 0 at each level of the
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hierarchy), by title, or by id.
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For example, if you have:
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menuentry 'Example GNU/Linux distribution' --class gnu-linux --id example-gnu-linux {
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...
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}
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then you can make this the default using:
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default=example-gnu-linux
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If the entry is in a submenu, then it must be identified using the
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number, title, or id of each of the submenus starting from the top
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level, followed by the number, title, or id of the menu entry itself,
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with each element separated by '>'. For example, take the following
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menu structure:
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GNU/Hurd --id gnu-hurd
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Standard Boot --id=gnu-hurd-std
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Rescue shell --id=gnu-hurd-rescue
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Other platforms --id=other
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Minix --id=minix
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Version 3.4.0 --id=minix-3.4.0
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Version 3.3.0 --id=minix-3.3.0
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GRUB Invaders --id=grub-invaders
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The more recent release of Minix would then be identified as 'Other
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platforms>Minix>Version 3.4.0', or as '1>0>0', or as
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'other>minix>minix-3.4.0'.
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This variable is often set by 'GRUB_DEFAULT' (*note Simple
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configuration::), 'grub-set-default', or 'grub-reboot'.
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15.1.11 fallback
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----------------
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If this variable is set, it identifies a menu entry that should be
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selected if the default menu entry fails to boot. Entries are
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identified in the same way as for 'default' (*note default::).
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15.1.12 gfxmode
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---------------
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If this variable is set, it sets the resolution used on the 'gfxterm'
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graphical terminal. Note that you can only use modes which your
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graphics card supports via VESA BIOS Extensions (VBE), so for example
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native LCD panel resolutions may not be available. The default is
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'auto', which selects a platform-specific default that should look
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reasonable. Supported modes can be listed by 'videoinfo' command in
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GRUB.
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The resolution may be specified as a sequence of one or more modes,
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separated by commas (',') or semicolons (';'); each will be tried in
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turn until one is found. Each mode should be either 'auto',
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'WIDTHxHEIGHT', or 'WIDTHxHEIGHTxDEPTH'.
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15.1.13 gfxpayload
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------------------
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If this variable is set, it controls the video mode in which the Linux
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kernel starts up, replacing the 'vga=' boot option (*note linux::). It
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may be set to 'text' to force the Linux kernel to boot in normal text
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mode, 'keep' to preserve the graphics mode set using 'gfxmode', or any
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of the permitted values for 'gfxmode' to set a particular graphics mode
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(*note gfxmode::).
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Depending on your kernel, your distribution, your graphics card, and
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the phase of the moon, note that using this option may cause GNU/Linux
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to suffer from various display problems, particularly during the early
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part of the boot sequence. If you have problems, set this variable to
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'text' and GRUB will tell Linux to boot in normal text mode.
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The default is platform-specific. On platforms with a native text
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mode (such as PC BIOS platforms), the default is 'text'. Otherwise the
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default may be 'auto' or a specific video mode.
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This variable is often set by 'GRUB_GFXPAYLOAD_LINUX' (*note Simple
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configuration::).
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15.1.14 gfxterm_font
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--------------------
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If this variable is set, it names a font to use for text on the
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'gfxterm' graphical terminal. Otherwise, 'gfxterm' may use any
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available font.
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15.1.15 grub_cpu
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----------------
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In normal mode (*note normal::), GRUB sets the 'grub_cpu' variable to
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the CPU type for which GRUB was built (e.g. 'i386' or 'powerpc').
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15.1.16 grub_platform
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---------------------
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In normal mode (*note normal::), GRUB sets the 'grub_platform' variable
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to the platform for which GRUB was built (e.g. 'pc' or 'efi').
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15.1.17 icondir
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---------------
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If this variable is set, it names a directory in which the GRUB
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graphical menu should look for icons after looking in the theme's
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'icons' directory. *Note Theme file format::.
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15.1.18 lang
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------------
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If this variable is set, it names the language code that the 'gettext'
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command (*note gettext::) uses to translate strings. For example,
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French would be named as 'fr', and Simplified Chinese as 'zh_CN'.
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'grub-mkconfig' (*note Simple configuration::) will try to set a
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reasonable default for this variable based on the system locale.
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15.1.19 locale_dir
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------------------
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If this variable is set, it names the directory where translation files
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may be found (*note gettext::), usually '/boot/grub/locale'. Otherwise,
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internationalization is disabled.
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'grub-mkconfig' (*note Simple configuration::) will set a reasonable
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default for this variable if internationalization is needed and any
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translation files are available.
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15.1.20 menu_color_highlight
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----------------------------
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This variable contains the foreground and background colors to be used
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for the highlighted menu entry, separated by a slash ('/'). Setting
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this variable changes those colors. For the available color names,
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*note color_normal::.
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The default is the value of 'color_highlight' (*note
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color_highlight::).
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15.1.21 menu_color_normal
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-------------------------
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This variable contains the foreground and background colors to be used
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for non-highlighted menu entries, separated by a slash ('/'). Setting
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this variable changes those colors. For the available color names,
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*note color_normal::.
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The default is the value of 'color_normal' (*note color_normal::).
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15.1.22 net_<INTERFACE>_boot_file
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---------------------------------
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*Note Network::.
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15.1.23 net_<INTERFACE>_dhcp_server_name
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----------------------------------------
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*Note Network::.
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15.1.24 net_<INTERFACE>_domain
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------------------------------
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*Note Network::.
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15.1.25 net_<INTERFACE>_extensionspath
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--------------------------------------
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*Note Network::.
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15.1.26 net_<INTERFACE>_hostname
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--------------------------------
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*Note Network::.
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15.1.27 net_<INTERFACE>_ip
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--------------------------
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*Note Network::.
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15.1.28 net_<INTERFACE>_mac
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---------------------------
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*Note Network::.
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15.1.29 net_<INTERFACE>_next_server
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-----------------------------------
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*Note Network::.
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15.1.30 net_<INTERFACE>_rootpath
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--------------------------------
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*Note Network::.
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15.1.31 net_default_interface
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-----------------------------
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*Note Network::.
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15.1.32 net_default_ip
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----------------------
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*Note Network::.
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15.1.33 net_default_mac
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-----------------------
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*Note Network::.
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15.1.34 net_default_server
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--------------------------
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*Note Network::.
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15.1.35 pager
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-------------
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If set to '1', pause output after each screenful and wait for keyboard
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input. The default is not to pause output.
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15.1.36 prefix
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--------------
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The location of the '/boot/grub' directory as an absolute file name
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(*note File name syntax::). This is normally set by GRUB at startup
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based on information provided by 'grub-install'. GRUB modules are
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dynamically loaded from this directory, so it must be set correctly in
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order for many parts of GRUB to work.
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15.1.37 pxe_blksize
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-------------------
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*Note Network::.
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15.1.38 pxe_default_gateway
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---------------------------
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*Note Network::.
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15.1.39 pxe_default_server
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--------------------------
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*Note Network::.
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15.1.40 root
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------------
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The root device name (*note Device syntax::). Any file names that do
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not specify an explicit device name are read from this device. The
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default is normally set by GRUB at startup based on the value of
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'prefix' (*note prefix::).
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For example, if GRUB was installed to the first partition of the
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first hard disk, then 'prefix' might be set to '(hd0,msdos1)/boot/grub'
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and 'root' to 'hd0,msdos1'.
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15.1.41 superusers
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------------------
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This variable may be set to a list of superuser names to enable
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authentication support. *Note Security::.
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15.1.42 theme
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-------------
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This variable may be set to a directory containing a GRUB graphical menu
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theme. *Note Theme file format::.
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This variable is often set by 'GRUB_THEME' (*note Simple
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configuration::).
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15.1.43 timeout
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---------------
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If this variable is set, it specifies the time in seconds to wait for
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keyboard input before booting the default menu entry. A timeout of '0'
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means to boot the default entry immediately without displaying the menu;
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a timeout of '-1' (or unset) means to wait indefinitely.
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If 'timeout_style' (*note timeout_style::) is set to 'countdown' or
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'hidden', the timeout is instead counted before the menu is displayed.
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This variable is often set by 'GRUB_TIMEOUT' (*note Simple
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configuration::).
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15.1.44 timeout_style
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---------------------
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This variable may be set to 'menu', 'countdown', or 'hidden' to control
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the way in which the timeout (*note timeout::) interacts with displaying
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the menu. See the documentation of 'GRUB_TIMEOUT_STYLE' (*note Simple
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configuration::) for details.
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15.2 The GRUB environment block
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===============================
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It is often useful to be able to remember a small amount of information
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from one boot to the next. For example, you might want to set the
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default menu entry based on what was selected the last time. GRUB
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deliberately does not implement support for writing files in order to
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minimise the possibility of the boot loader being responsible for file
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system corruption, so a GRUB configuration file cannot just create a
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file in the ordinary way. However, GRUB provides an "environment block"
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which can be used to save a small amount of state.
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The environment block is a preallocated 1024-byte file, which
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normally lives in '/boot/grub/grubenv' (although you should not assume
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this). At boot time, the 'load_env' command (*note load_env::) loads
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environment variables from it, and the 'save_env' (*note save_env::)
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command saves environment variables to it. From a running system, the
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'grub-editenv' utility can be used to edit the environment block.
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For safety reasons, this storage is only available when installed on
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a plain disk (no LVM or RAID), using a non-checksumming filesystem (no
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ZFS), and using BIOS or EFI functions (no ATA, USB or IEEE1275).
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'grub-mkconfig' uses this facility to implement 'GRUB_SAVEDEFAULT'
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(*note Simple configuration::).
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