Which grub is active

How can I discover which bootloader is installed where? Ask Question. Asked 9 years, 2 months ago. Active 8 years, 8 months ago.

Viewed 26k times. Improve this question. Norman Ramsey Norman Ramsey 2, 8 8 gold badges 28 28 silver badges 41 41 bronze badges. Have you pressed the "Esc" key to display Grub's boot menu before the error message appears? Just "Grub loading; Welcome to Grub;" and then the error. Normally I would expect a menu and then autoboot after a timeout of 10s. But I'm not getting that far. Hence the question about "how do I figure out what is there.

Add a comment. Active Oldest Votes. Improve this answer. That's important, otherwise you will keep overwriting your config. In case Grub2 is installed in its own boot partition, you don't need to change anything.

When it is not which would be really strange , then you could technically retain the grub. If you run mount and see something like this:. You have Grub2 installed in its own partition, as it should be. Normally, when installing a new distro, the wizzard will usually guide you through the installation process, and even figure out what partitions contain what OS-es, if applicable.

The process on Arch is a bit more tedious but very well documented. At this point I'm not sure if partitions need to be all mounted for Grub2 to detect the OS-es on them, though. If you tried to install Windows in the mean time, it might be Windows overwrote the boot loader. To fix that, simply run as root or with sudo :. Grub2 is a Stage-2 boot loader. The rest of the line is passed verbatim as the module command line.

Next: nativedisk , Previous: module , Up: Command-line and menu entry commands [ Contents ][ Index ]. Load a multiboot kernel image from file. Any module must be reloaded after using this command see module. Some kernels have known problems. GRUB prior to 0. Use this option to ignore kludge. Known affected systems: old Solaris, SkyOS. Known afftected systems: VMWare. Switch from firmware disk drivers to native ones. Really useful only on platforms where both firmware and native disk drives are available.

In normal mode, commands, filesystem modules, and cryptography modules are automatically loaded, and the full GRUB script parser is available. Other modules may be explicitly loaded using insmod see insmod. If a file is given, then commands will be read from that file. It is more usual to use configfile see configfile for this. Exit normal mode see normal.

If this instance of normal mode was not nested within another one, then return to rescue mode. On these partition tables, the following commands are available:. When enabled, this makes the selected partition be the active bootable partition on its disk, clearing the active flag on all other partitions.

This command is limited to primary partitions. Change the type of an existing partition. When enabled, this hides the selected partition by setting the hidden bit in its partition type code; when disabled, unhides the selected partition by clearing this bit.

Define a user named user with password clear-password. Define a user named user with password hash hashed-password. Use grub-mkpasswd-pbkdf2 see Invoking grub-mkpasswd-pbkdf2 to generate password hashes.

If the argument is a file name see File name syntax , play the tune recorded in it. The file format is first the tempo as an unsigned 32bit little-endian number, then pairs of unsigned 16bit little-endian numbers for pitch and duration pairs.

The tempo is the base for all note durations. Pitches are Hz. Set pitch to 0 to produce a rest. Retrieve device information. If option --set is given, assign result to variable var , otherwise print information on the screen.

Read a model-specific register at address 0xADDR. Also, if you specify a reserved or unimplemented MSR address, it will cause a general protection exception which is not currently being handled and the system will reboot.

Read a line of input from the user. If an environment variable var is given, set that environment variable to the line of input that was read, with no terminating newline.

Test if regular expression regexp matches string. If option --set is given, store number th matched subexpression in variable var. Save the named variables from the environment to the environment block file. It is possible to modify a digitally signed environment block file from within GRUB using this command, such that its signature will no longer be valid on subsequent boots.

Care should be taken in such advanced configurations to avoid rendering the system unbootable. Search devices by file -f , --file , filesystem label -l , --label , or filesystem UUID -u , --fs-uuid. If the --set option is used, the first device found is set as the value of environment variable var. Insert keystrokes into the keyboard buffer when booting. Sometimes an operating system or chainloaded boot loader requires particular keys to be pressed: for example, one might need to press a particular key to enter "safe mode", or when chainloading another boot loader one might send keystrokes to it to navigate its menu.

You may provide up to 16 keystrokes the length of the BIOS keyboard buffer. Keystroke names may be upper-case or lower-case letters, digits, or taken from the following table:. As well as keystrokes, the sendkey command takes various options that affect the BIOS keyboard status flags. The --num , --caps , --scroll , and --insert options emulate setting the corresponding mode, while the --numkey , --capskey , --scrollkey , and --insertkey options emulate pressing and holding the corresponding key.

The other status flag options are self-explanatory. If the --no-led option is given, the status flag options will have no effect on keyboard LEDs. If the sendkey command is given multiple times, then only the last invocation has any effect. Since sendkey manipulates the BIOS keyboard buffer, it may cause hangs, reboots, or other misbehaviour on some systems.

If the operating system or boot loader that runs after GRUB uses its own keyboard driver rather than the BIOS keyboard functions, then sendkey will have no effect. Set the environment variable envvar to value. If invoked with no arguments, print all environment variables with their values. Alias for hashsum --hash sha1 arg ….

Next: shasum , Previous: sha1sum , Up: Command-line and menu entry commands [ Contents ][ Index ]. Alias for hashsum --hash sha arg …. Sleep for count seconds.

With --verbose show countdown of remaining seconds. Exit code is set to 0 if timeout expired and to 1 if timeout was interrupted using any of the mentioned keys. The following options determine which structure to select. Only one of these options may be specified at a time.

The default action is to print the value of the requested field to the console, but a variable name can be specified with --set to store the value instead of printing it. Read file as a configuration file, as if its contents had been incorporated directly into the sourcing file. Unlike configfile see configfile , this executes the contents of file without changing context: any environment variable changes made by the commands in file will be preserved after source returns, and the menu will not be shown immediately.

Evaluate expression and return zero exit status if result is true, non zero status otherwise. Optionally numeric bias may be directly appended to -nt in which case it is added to the first file modification time. Optionally numeric bias may be directly appended to -ot in which case it is added to the first file modification time.

Do nothing, successfully. It is expected that --skip-sig is useful for testing and manual booting. If validation fails, it is set to a non-zero value. Load a Xen hypervisor binary from file. Any other binaries must be reloaded after using this command. This command is only available on AArch64 systems. Load a module for xen hypervisor at the booting process of xen. Modules should be loaded in the following order: - dom0 kernel image - dom0 ramdisk if present - XSM policy if present This command is only available on AArch64 systems.

Configure additional network interface with address on a network card. Add route to network with address ip as modified by prefix via either local interface or gateway. Perform configuration of card using DHCP protocol. If no card name is specified, try to configure all existing cards.

Additionally the following DHCP options are recognized and processed:. Note that only option with single route is accepted. Request DHCP option number of type via interface. If option is found, assign its value to variable var. If no card is specified, perform autoconfiguration for all existing cards.

Resolve address of name using DNS server server. If no server is given, use default list of servers. All text files including config are assumed to be encoded in UTF GRUB handles filesystem case-insensitivity however no attempt is performed at case conversion of international characters so e. On ZFS subvolumes marked as case insensitive files containing lowercase international characters are inaccessible.

On normalized ZFS subvolumes filenames out of normalisation are inaccessible. None of above mentioned is appropriate for displaying international and any unsupported character is replaced with question mark except pseudographics which we attempt to approximate with ASCII. EFI console on the other hand nominally supports UTF but actual language coverage depends on firmware and may be very limited.

When using gfxterm or gfxmenu GRUB itself is responsible for rendering the text. In this case GRUB is limited by loaded fonts. If fonts contain all required characters then bidirectional text, cursive variants and combining marks other than enclosing, half e. Notable unsupported scripts are Brahmic family and derived as well as Mongolian, Tifinagh, Korean Jamo precomposed characters have no problem and tonal writing 2ee9. GRUB also ignores deprecated as specified in Unicode characters e.

EFI specification allows for such but author is unaware of any actual implementations. Serial input is currently limited for latin1 unlikely to change. So no dead keys or advanced input method. Also there is no keymap change hotkey. In practice it makes difficult to enter any text using non-Latin alphabet. GRUB supports being translated. Regexps work on unicode characters, however no attempt at checking cannonical equivalence has been made.

GRUB always uses the decimal number format with [] as digits and. Similar behaviour is for matching OSBundleRequired. Case-sensitive identifiers are matched as raw strings, no canonical equivalence check is performed. By default, the boot loader interface is accessible to anyone with physical access to the console: anyone can select and edit any menu entry, and anyone can get direct access to a GRUB shell prompt. For most systems, this is reasonable since anyone with direct physical access has a variety of other ways to gain full access, and requiring authentication at the boot loader level would only serve to make it difficult to recover broken systems.

However, in some environments, such as kiosks, it may be appropriate to lock down the boot loader to require authentication before performing certain operations. Superusers are permitted to use the GRUB command line, edit menu entries, and execute any menu entry. If the --unrestricted option is used for a menu entry, then that entry is unrestricted. If the --users option is not used for a menu entry, then that only superusers are able to use it. The grub-mkconfig program does not yet have built-in support for generating configuration files with authentication.

If validation fails, then file foo cannot be opened. This failure may halt or otherwise impact the boot process. An initial trusted public key can be embedded within the GRUB core. A signing key can be generated as follows:. One way to accomplish this is the following after having already produced the desired grub. Note that signature checking does not prevent an attacker with serial, physical, To prevent this, password-protection see Authentication and authorisation is essential.

GRUB is at best only one link in a secure boot chain. It is built into the core. All GRUB modules not stored in the core. Additionally, the commands that can be used to subvert the UEFI secure boot mechanism, such as iorw and memrw will not be available when the UEFI secure boot is enabled.

The SBAT metadata is located in an. To add a data section containing the SBAT information into the binary, the --sbat option of grub-mkimage command should be used.

The CSV file can be stored anywhere on the file system. GRUB will not measure its own core. GRUB will also not perform any measurements until the tpm module is loaded. As such it is recommended that the tpm module be built into core. Otherwise it does not exit. GRUB2 is designed to be portable and is actually ported across platforms. We try to keep all platforms at the level. Unfortunately some platforms are better supported than others. This is detailed in current and 2 following sections.

In some cases, larger disk sizes can be used, but access will not be allowed beyond 1 EiB. They can not be created as crypto devices by cryptomount, so can not even be partially read from.

LUKS have no limitations other than those imposed by the format. EMU has similar limitation. Console charset refers only to firmware-assisted console. Loongson always uses gfxterm. CP provides additionally pseudographics. Unicode is the most versatile charset which supports many languages. However the actual console may be much more limited depending on firmware. On BIOS, network is supported only if the image is loaded through network.

On sparc64, GRUB is unable to determine which server it was booted from. AT keyboard support allows keyboard layout remapping and support for keys not available through firmware. In addition it allows USBserial. Hints allow faster disk discovery by already knowing in advance which is the disk in question.

On some platforms hints are correct unless you move the disk between boots. Note that hint failure results in just reduced performance, not a failure. Bootlocation is ability of GRUB to automatically detect where it boots from. For consistency, default install ignores partition and relies solely on disk detection. If no bootlocation discovery is available or boot and grub-root disks are different, UUID is used instead. Some platforms have features which allows to implement some commands useless or not implementable on others.

X86 support is summarised in the following table. As you have seen in previous chapter the support matrix is pretty big and some of the configurations are only rarely used. All x86 platforms have bootcheck facility except ieee Multiboot, multiboot2, BIOS chainloader, ntldr and freebsd-bootloader boot targets are tested only with a fake kernel images.

Only Linux is tested among the payloads using Linux protocols. However, any problem that leaves you in the rescue shell probably means that GRUB was not correctly installed. It may be more useful to try to reinstall it properly using grub-install device see Invoking grub-install. When doing this, there are a few things to remember:. Affected are models of year or earlier. Workaround is to zeroize the bytes to of the EFI partition, where mformat has put a partition table entry which claims partition start at block 0.

This change will not hamper bootability on other machines. The program grub-install generates a GRUB core image using grub-mkimage and installs it on your system. You must specify the device name on which you want to install GRUB, like this:. By default on x86 BIOS systems, grub-install will use some extra space in the bootloader embedding area for Reed-Solomon error-correcting codes.

This enables GRUB to still boot successfully if some blocks are corrupted. The exact amount of protection offered is dependent on available space in the embedding area. This redundancy may be cumbersome if attempting to cryptographically validate the contents of the bootloader embedding area, or in more modern systems with GPT-style partition tables see BIOS installation where GRUB does not reside in any unpartitioned space outside of the MBR.

Disable the Reed-Solomon codes with this option. Send the generated configuration file to file. The default is to send it to standard output. The program grub-mkrelpath makes a file system path relative to the root of its containing file system.

This is mainly used internally by other GRUB utilities such as grub-mkconfig see Invoking grub-mkconfig , but may occasionally also be useful for debugging. All arguments not explicitly listed as grub-mkrescue options are passed on directly to xorriso in mkisofs emulation mode. Non-option arguments specify additional source directories.

This is commonly used to add extra files to the image:. Pre-load the named GRUB modules in the image. Multiple entries in modules should be separated by whitespace so you will probably need to quote this for your shell.

This has a number of uses:. Load a ZFS encryption key. Set the GRUB root device to device. You do not normally need to set this; grub-mount will automatically set the root device to the root of the supplied file system. If device is just a number, then it will be treated as a partition number within the supplied image.

This means that, if you have an image of an entire disk in disk. Print information about the given path or device as defined by target. The available targets and their meanings are:. A string of platform search hints suitable for passing to the search command see search. A guess at a reasonable GRUB drive name for this device, which may be used as a fallback if the search command fails. The program grub-script-check takes a GRUB script file see Shell-like scripting and checks it for syntax errors, similar to commands such as sh -n.

It may take a path as a non-option argument; if none is supplied, it will read from standard input. Caution: GRUB requires binutils The file will be named grub-version. The current version is 2. Also, the latest version is available using Git. These are the guideline for how to report bugs. Take a look at this list below before you submit bugs:. The information on your hardware is also essential.

These are especially important: the geometries and the partition tables of your hard disk drives and your BIOS. When you attach a patch, make the patch in unified diff format, and write ChangeLog entries. If you follow the guideline above, submit a report to the Bug Tracking System. Alternatively, you can submit a report via electronic mail to bug-grub gnu. GRUB 2 is now quite stable and used in many production systems.

We are currently working towards a 2. If you are interested in the development of GRUB 2, take a look at the homepage. The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially.

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