||<>|| This page provides the user with information on options available for repairing GRUB 2 boot issues and specific instructions on how to use the GRUB 2 terminal. The instructions are written for GRUB 1.99, which is the version of GRUB 2 which is included on Ubuntu 11.04, Natty Narwhal, and later. Differences for version 1.98 (Ubuntu 10.4, Lucid Lynx) are noted when the procedures differ. {{attachment:g2_grub_rescue1.png}} GRUB 2's ability to fix boot problems is greatly improved over the original GRUB bootloader. In addition to an automatic fallback mode if booting from a menuentry in a submenu, GRUB 2 allows the user to edit its menu before the operating system is loaded. The ''rescue mode'' GRUB 2 terminal can help boot an operating system so that permanent repairs to system files can be made. The instructions on this page are written for a fully-installed Ubuntu operating system. WUBI boot problems are not covered in detail although they are addressed in several sections. = Overview = GRUB 2 boot problems can leave the system in several states. The user may see one of the following displays on the monitor when a boot fails. The display provides the first indication of what might be causing the failure to boot. Here are the failure prompts and displays, and the possible cause of each: * ''grub>'' prompt: GRUB 2 loaded modules but was unable to find the grub.cfg file. * ''grub rescue>'' prompt: GRUB 2 failed to find its ''grub'' folder, or failed to load the ''normal'' module. * [[#grub>|grub>:]] - The ''grub'' prompt on a blank screen. GRUB 2 has found the boot information but has been either unable to locate or unable to use an existing GRUB 2 configuration file (usually ''grub.cfg''). * [[grub rescue>|grub rescue>:]] - The rescue mode. GRUB 2 is unable to find the ''grub'' folder or its contents are missing/corrupted. The ''grub'' folder contains the GRUB 2 menu, modules and stored environmental data. * [[#GRUB|GRUB]] - a single word at the top left of the screen, with no prompt and no cursor. GRUB has failed to find even the most basic information, usually contained in the MBR or boot sector. * ''Busybox'' or ''Initramfs'': GRUB 2 began the boot process but there was a problem passing control to the operating system. Possible causes include an incorrect UUID or ''root='' designation in the 'linux' line or a corrupted kernel. * Frozen splash screen, blinking cursor with no ''grub>'' or ''grub rescue'' prompt. Possible video issues with the kernel. While these failures are not of GRUB 2's making, it may still be able to help. GRUB 2 allows pre-boot editing of its menu and the user may restore functionality by adding and/or removing kernel options in a ''menuentry'' before booting. Each of the GRUB 2 failure modes can normally be corrected either from the GRUB 2 terminal or by using an Ubuntu LiveCD. Additionally, there are compatible 3rd party bootable "rescue" CD/USB options which may also work. If using an Ubuntu LiveCD, it is recommended, but not always necessary, to use the same version CD as the system you are trying to repair. This ensures compatability of any modules and configuration files that may be loaded while attempting to repair the system. = GRUB 2 Terminal Commands = {{attachment:info.png}} Here are some useful tips and features for use with the GRUB 2 terminal: * '''Turning off the splash image'''. This may make viewing the terminal easier. Press '''c''' at the GRUB 2 menu to get to the command line and then type: `set color_normal=white/blue` or the color combination you wish to use. "black" as the second entry retains the menu's transparency and should be avoided as a selection if the user wants to work with a solid background color. * '''TAB completion'''. This feature is very handy. At any point, pressing the TAB key may complete an entry, if the element is unique, or display available options. Typing a few additional characters and pressing TAB again may allow ''tab completion'' to finish the entry. * '''set pager=1''' To prevent text from scrolling off the screen, type '''set pager=1'''. * '''Help'''. Type `help` to view a list of all the commands. Type `help x` to view help commands beginning with the letter "x". Tab completion and using the up arrow to repeat commands work the same as in a normal terminal. == Normal == When GRUB 2 is fully functional, the GRUB 2 terminal is accessed by pressing '''c'''. If the menu is not displayed during boot, hold down the SHIFT key until it appears. If it still does not appear, try pressing the ESC key repeatedly. From a GRUB 2 terminal with the ''grub>'' prompt, a wide variety of commands are available. A few of the more important commands: ||<25%>'''Command'''||'''Result / Example''' || ||boot||Initiate the boot sequence, also F10 or CTRL-x || ||cat||Display the contents of readable files; ''cat (hd0,1)/boot/grub/grub.cfg''|| ||configfile||Load a GRUB 2 configuration file such as grub.cfg; ''configfile (hd0,5)/boot/grub/grub.cfg''|| ||initrd||Loads the initrd.img, necessary for booting; ''initrd (hd0,5)/initrd.img''|| ||insmod||Loads a module; ''insmod (hd0,5)/boot/grub/normal.mod'', or ''insmod normal'' || ||linux||Loads the kernel; ''insmod /vmlinuz root=(hd0,5) ro'' || ||loop||Mount a file as a device; ''loopback loop (hd0,2)/iso/my.iso''|| ||ls||Lists the contents of a partition/folder; ''ls'', ''ls /boot/grub'', ''ls (hd0,5)/'', ''ls (hd0,5)/boot'' || ||lsmod||List loaded modules || ||normal||Activate the ''normal'' module, if loaded|| ||search||Search for a device. Type ''help search'' for the available options. || ||set||Review current settings, or ''set XXX'' to set a variable such as colors, prefix, root || ||vbeinfo||Display GRUB 2 available resolutions || To view the complete command list, type '''help'''. For details on a particular command, type '''help [command]''' == grub> == When GRUB 2 is unable to boot or display the GRUB 2 menu the system will be left at a GRUB 2 terminal if possible. If the system boots to the ''grub>'' prompt, the usual modules and commands are normally available. The user may need to manually load modules using the '''insmod [module]''' command before some commands will work. == grub rescue> == In the ''grub rescue'' mode, only a limited set of commands are available. These commands are sufficient to investigate the contents of the drives, set ''prefix'' (path to the grub folder) and ''root'' (partition), load modules and boot. The ''rescue'' mode provides fewer commands than the normal GRUB prompt line, but also provides these additional commands: ||<25%>'''Command'''||'''Result / Example''' || ||dump||Clears memory|| ||exit||Exit GRUB 2|| ||normal||Return to the standard "grub>" mode if possible.|| Among the commands which can be used in the grub rescue mode: ||<15%>boot||<15%>cat||<15%>chain||<15%>help||<15%>insmod||<15%>linux|| ||ls||multiboot||normal||search||set||unset|| = General Troubleshooting Preparation = == Boot-Repair == The majority of this guide is devoted to working with the GRUB 2 terminal, which is used to enter commands to attempt to repair a broken bootloader. {{attachment:info.png}} [[https://help.ubuntu.com/community/Boot-Repair|Boot-Repair]] is a GUI application which can automatically analyze boot problems and select the proper course of action to repair them. Its simple interface provides beginners as well as experienced Linux users an easy method of repairing the majority of GRUB 2 problems. Additionally, Boot-Repair contains an automated method to run a ''boot info'' script which performs a series of tests and provides a file containing much valuable information regarding the status of the computer's operating and boot systems. This file can be inspected by community helpers on forums or IRC channels to help diagnose boot problems. Boot-Repair can be run from a LiveCD or an operating Linux system. To download the package run the following commands: {{{ sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update sudo apt-get install -y boot-repair && boot-repair }}} Visit the [[https://help.ubuntu.com/community/Boot-Repair|Boot-Repair]] community document for more information. Boot-Repair is available from the Launchpad repositories and can be run from a CD or a working Linux OS. == Search & Set == A great many boot problems are due to incorrect paths to required files. The GRUB 2 terminal, in either 'failure' mode, provides a robust ability to search hard drive(s) and partitions and to inspect their contents. '''In order to boot successfully, the '''''root, prefix, linux and initrd''''' variables must be correct. The user must verify the paths and names of these items. If they are incorrect, use the commands below to find and fix them. GRUB 2 variable settings can be viewed with the '''set''' command. ''' In the following examples, '''X''' is a hard drive number; '''Y''' is a partition number. If a command example includes either of these replace them with the appropriate value. === How & Where to Search === In the graphic below, the text in red are commands to be entered by the user, and text in green is the output of the command ''on an operating system'' (i.e. what you would like to see if your Ubuntu installation is on ''sda1''). {{attachment:g2_grub_set_color.png}} * The first hard drive is ''0''. The first partition is ''1''. Thus sda1 becomes ''(hd0,1)'', sdb5 is ''(hd1,5)''. * Use the '''ls''' command in the follow manner * "Tab completion" may work - enter part of the filename and press the TAB key. ||<20%>'''Command'''||'''Purpose'''|| ||'''ls'''||Search the entire computer for devices and partitions: (hd0) (hd1) (hd0,1) (hd0,5) (hd1,1)|| ||'''ls /'''||Search the root directory of the device designated as root (use the '''set''' command to check root).|| ||'''ls (hdX,Y)'''||View information about a partition - format, size, UUID, etc.|| ||'''ls (hdX,Y)/'''||View the root contents of a partition. Use this command to look for the presence of ''vmlinuz'' and ''initrd.img'' symlinks|| ||'''ls (hdX,Y)/boot/'''||View the contents of a folder|| ||'''ls (hdX,Y)/boot/'''||Inspect the /boot folder. It should contain the actual kernel (linux-3.2...) and initrd image (initrd.img-3.2....)|| ||<^>'''ls (hdX,Y)/boot/grub/'''||Inspect the /boot/grub folder. It should contain ''grub.cfg'' and many *.mod files. If looking for a specific file, include the name in the search to limit the number of returns. If available, the command '''''set pager=1''''' will also limit returns to a single screen.|| ||'''What to Look For'''||'''Where It Should Be''' (Default Installation)||'''Specific / General Search Example'''|| ||grub.cfg||''(hdX,Y)/boot/grub/'' or ''/boot/grub/''||'''ls (hdX,Y)/boot/grub/grub.cfg''' or '''ls /boot/grub/'''|| ||vmlinuz||''(hdX,Y)/'' or ''/''||'''ls (hdX,Y)/vmlinuz''' or '''ls /vmlinuz''' or '''ls /'''|| ||linux-3.2.0-14*||''(hdX,Y)/boot/'' or ''/boot/''||'''ls (hdX,Y)/boot/vmlinuz-3.2.0-14'''|| ||initrd||''(hdX,Y)/'' or ''/''||'''ls (hdX,Y)/''' or '''ls /initrd'''|| ||initrd.img-3.20-14||''(hdX,Y)/'' or ''/boot/''||'''ls (hdX,Y)/boot/initrd.img-3.20-14''' or '''ls (hdX,Y)/boot/'''|| * Note: Use the full kernel name, including ''-generic'', when searching or setting a kernel variable. Using the "TAB completion" technique may eliminate some typing and be more accurate if available. Use the following commands to '''set''' these parameters (if incorrect). Substitute the correct value for '''X''' and '''Y'''. (Example: ''set root=(hdX,Y)'' becomes ''set root=(hd0,5)'' ) ||'''Task'''||'''Command'''||'''Notes'''|| ||Set the ''prefix''||'''set prefix=(hdX,Y)/boot/grub'''||Use the actual location of the ''grub'' folder|| ||Set ''root''||'''set root=(hdX,Y)'''|||| ||Set the kernel||'''linux /vmlinuz root=/dev/sda1 ro'''||Set the kernel if the symlink ''vmlinuz'' exists in /|| ||Set the kernel||'''linux (hdX,Y)/boot/vmlinuz-3.0.2-14 root=/dev/sda1 ro'''||Set the kernel itself|| ||Set the initrd image||'''initrd /initrd.img'''||Set the initrd image if the symlink exists in /|| ||Set the initrd image||'''initrd (hdX,Y)/boot/initrd.img-3.0.2-14'''||Set the initrd image itself|| = Specific Troubleshooting = Use the section below based on the type of GRUB 2 terminal prompt displayed on the monitor. {{attachment:important.png}} The commands which follow assume you have determined the proper parameters for '''prefix''', '''root''', '''linux''', and '''initrd'''. Review the [[#Search & Set|Search & Set]] section of this page for guidance . == grub> == Terminal Display: The GRUB 2 header/version information and a '''grub>''' prompt. {{attachment:g2_grub>.png}} If GRUB 2 leaves you at the ''grub>'' prompt, it has normally found the ''grub'' folder and loaded at least some basic modules. The configuration file (''grub.cfg'') may be missing, misnamed, or corrupted. '''Quick Fix:''' Use the [[#Search & Set|Search & Set]] section to confirm the correct paths are set. Inspect the contents of the ''/boot/grub'' folder. Look for the ''grub.cfg'' file. It could be misnamed or missing. If not located in ''/boot/grub'', use the ''ls'' command look for another ''.cfg'' file or look in ''/boot'' or other locations. If you locate the correct .cfg file: 1. '''configfile /boot/grub/grub.cfg''' or '''configfile (hdX,Y)/boot/grub/grub.cfg''' If a ''.cfg'' with another name is located, substitute its path/filename in the command. If the configuration file is loaded and not corrupt, when the above command is executed the GRUB 2 menu should appear and the user can make a selection to boot. Once booted into the system, correct the filename or move the configuration file to its proper location. Run `update-grub`. If the configuration file is not found, a message will be generated and the user must enter the boot commands manually. '''Extended Fix:''' The following commands should set the ''root'' and ''prefix'' paths and load the kernel and initrd image. With this information, GRUB 2 does not need a configuration file and should be able to boot the system if the only problem was a corrupted or missing menu. * Press ''~-ENTER-~'' after completing each line. Some entries will not provide feedback. This is normal. * If a "file not found" or similar error message is displayed while running these commands, ensure you are using the correct ''X,Y'' values and the correct paths are set. ||<(|2 tablewidth="95%" 30% ^>1. '''set root=(hd''X,Y'')'''||Confirm the correct X,Y values and press ''~-ENTER-~''. || ||Example: If the Ubuntu system is on sda5, enter: ''set root=(hd0,5)''|| ||<(|4 ^>2. '''linux /vmlinuz root=/dev/sd''XY'' ro'''||Example: ''linux /vmlinuz root=/dev/sda5 ro''|| ||If the ''vmlinuz'' symlink does not exist, use the full path to the kernel in /boot|| ||Example: linux /boot/vmlinuz-3.2.0-14-generic root=/dev/sda1 ro|| ||If successful, after ~-ENTER-~ there will be a slight delay and no messages.|| '''Wubi''' users only - substitute these commands in Steps 1 and 2: ||<(^ 25%>1.'''set root=(loop0)'''|| ||<(^>2. '''linux /vmlinuz root=/dev/sd''XY'' loop=/ubuntu/disks/root.disk ro'''|| ||<(|3 tablewidth="95%" 30% ^>3. '''initrd /initrd.img'''||Selects the latest initrd image.|| ||If the ''vmlinuz'' symlink does not exist, use the full path to the initrd image in /boot|| ||If successful, after ~-ENTER-~ there will be a slight delay and no messages.|| ||<(^>4. '''boot''' ||Boot to the latest kernel on the selected partition.|| If the system fails to boot: 1. Attempt to find the GRUB 2 configuration file. The normal name is ''grub.cfg'' file. If not found, look for a misnamed ''.cfg'' file or in alternate locations. The menu configuration file may contain settings required for a successful boot (such as non-standard kernel options) even if the paths/filenames are correct. 1. Use the '''set''' command to confirm the correct ''root'' and ''prefix'' settngs. Also inspect the folders' actual contents with the '''ls''' command. The ''grub'' prompt normally means the ''GRUB 2'' folder is intact but doesn't guarantee the integrity of other system files. 1. ''root='' should point to the drive and partition on which Ubuntu is installed. If you use the '''ls /''' command you should see the main Ubuntu system folders. If the system boots, please refer to the [[#Post-Boot Follow Up|Post Boot Follow Up] section If the system fails to boot, proceed to the [#grub rescue|grub rescue]] section for more detailed troubleshooting options. == grub rescue> == The GRUB 2 ''rescue'' mode is a major enhancement to the GRUB bootloader. The presence of the ''grub rescue>'' prompt signifies that GRUB 2 has failed to find the ''grub'' folder, the ''grub.cfg'' file, and/or the associated modules. The rescue prompt is presented so the user can provide the path to the ''grub'' folder, load the necessary modules, and provide the proper boot commands. {{attachment:g2_grub_rescue.png}} A common reason for the ''grub rescue>'' prompt is an incorrect path to the ''grub'' folder. Reasons for the prompt also include a failure to update GRUB 2 after certain system or partition operations, improper designation of the ''grub'' folder location, missing ''linux'' or ''initrd.img'' symlinks in /, or a failed installation. To successfully boot from the ''grub rescue>'' prompt: * The ''grub'' folder must exist and contain the necessary GRUB 2 files and modules. * The proper paths must be set via the '''set prefix''' command. Many GRUB 2 commands will not work until the correct path is set. If the path to the ''grub'' folder (normally ''/boot/grub'') is not correct, an ''unknown command'' or ''file not found'' message is likely. * The necessary modules must be loaded. The kernel cannot be loaded until the 'linux' module is loaded. * A Linux kernel and initrd.img must be located and loaded. Use the ''[[#General Troubleshooting Preparation|General Troubleshooting Preparation]]'' section to locate the correct partitions and file locations. Once the user has confirmed the paths and existence of the proper folders using the [[#Search & Set|Search & Set]] section, run the following commands: ||<(|2 tablewidth="95%" 30% ^>1. '''set prefix=(hd''X,Y'')/boot/grub'''||Use the values determined earlier.|| ||Example: If the Ubuntu system is on sda5, enter: ''set prefix=(hd0,5)/boot/grub''|| ||<(|2 tablewidth="95%" 30% ^>2.* '''set root=(hd''X,Y'')'''||Confirm the correct X,Y values and press ''~-ENTER-~''. || ||Example: If the Ubuntu system is on sda5, enter: ''set root=(hd0,5)''|| ||<(|3 ^>3. '''insmod normal'''||Load the ''normal'' module.|| ||If the module loads there will be no message.|| ||If the module fails to load, try the full path: ''insmod (hdX,Y)/boot/grub/normal.mod''|| ||<(|3 ^>4. '''normal'''||Transition to the normal GRUB 2 mode with increased functionality.|| ||If the module loads there will be no message.|| ||If the module loads, ''HELP'', TAB completion and command recall using the UP/DN keys should be available.|| ||<(^>5. '''set'''||(Optional) Review the current settings.|| ||<(^>6. '''insmod linux'''||Load the ''linux'' module. An error message usually means the path is incorrect. || ||<(|4^>7.* '''linux /vmlinuz root=/dev/sdXY ro'''||Selects the latest kernel.|| ||Example: ''linux /vmlinuz root=/dev/sda5 ro'' || ||If the ''vmlinuz'' symlink does not exist in /, use the full path to the kernel in /boot|| ||Example: linux /boot/vmlinuz-3.2.0-14-generic root=/dev/sda1 ro|| ||<(|3 ^>8. '''initrd /initrd.img'''||Selects the latest initrd image.|| ||If the ''initrd'' symlink does not exist in /, use the full path to the initrd image in /boot|| ||If successful, after ~-ENTER-~ there will be a slight delay and no messages.|| ||<(^>9. '''boot''' ||Boot to the latest kernel on the selected partition.|| '''* Wubi''' users only - substitute these commands in Steps 2 and 7: ||<(^ 25%>1.'''set root=(loop0)'''|| ||<(^>2. '''linux /vmlinuz root=/dev/sd''XY'' loop=/ubuntu/disks/root.disk ro'''|| Some additional considerations: * The current ''prefix'' and ''root'' settings may be checked at any time with the ''set'' command. To remove a setting, use the ''unset'' command. Example: '''unset prefix''' * Modules must be loaded before they can be used. If a module has not been loaded a ''unknown command'' error is displayed. If an incorrect path is specified, a ''file not found'' error message may be displayed. * The ''linux'' module must be loaded to be able to load both the kernel and the initrd image unless the ''normal'' module is loaded first. * If the modules cannot be found in the ''/boot/grub'' folder, the user may be able to load them from the ''/usr/lib/grub/i386-pc'' folder. The address if Ubuntu was installed on sda1 would be ''(hd0,1)/usr/lib/grub/i386-pc'' and the command would be: '''insmod (hd0,1)/usr/lib/grub/i386-pc/normal.mod''' Refer to the [[#Post Boot Follow Up|Post Boot Follow Up]] section if the system successfully boots. == GRUB == Presence of the word ''GRUB'' at the top left of the monitor with no blinking cursor indicates that GRUB 2 can not even find the Master Boot Record (or equivalent) information. Thus, the ''core.img'' file, the ''/boot'' and ''/grub'' folder locations and contents are completely unknown to GRUB 2. {{attachment:g2_grub_fail.png}} The seriousness of the problem cannot be assessed without the use of another operating system or an Ubuntu LiveCD or equivalent. The Ubuntu partition should be mounted for inspection and the user can then check to see if the system files are intact. If so, the user can use the [[https://help.ubuntu.com/community/Grub2/Installing#ChRoot|''ChRoot'']] procedure from the LiveCD to reinstall GRUB 2 and rewrite the information to the MBR. Details on this procedure are contained in the [[https://help.ubuntu.com/community/Grub2/Installing|Grub2/Installing]] community documentation. = Editing the GRUB 2 Menu During Boot = Following a failed boot, GRUB 2 is designed to display the GRUB 2 menu on the next boot and await user input. This will happen even if the user has set the system to boot without displaying the GRUB 2 menu. This provides the user the opportunity to select a different menu option or edit a menuentry to change boot parameters. While this can cause problems on a server, for most users it is a benefit which will prevent constant rebooting during unmonitored operations. {{attachment:g2_grub_edit_menu.png}} In addition to its troubleshooting benefits, pre-boot editing of the GRUB 2 menu also allows users to add or remove kernel options, change operating modes, and accomplish other tasks such as [[https://help.ubuntu.com/community/Grub2/Displays#Testing_Fonts_and_Splash_Images|testing fonts and splash images]]. For users who like to experiment, the settings altered via the GRUB 2 terminal are non-persistent and won't affect future boots. == Key Points About Terminal Menu Editing: == * If the menu is displayed, the automatic countdown may be stopped by pressing any key other than the ENTER key. * If the menu is not normally displayed during boot, hold down the SHIFT key as the computer attempts to boot to display the GRUB 2 menu. * In certain circumstances, if holding the SHIFT key method does not display the menu pressing the ESC key repeatedly may display the menu. * Press the 'e' key to reveal the selection's settings. * Use the UP/DN/Left/Right cursor keys to navigate to the desired point for editing. * Make a single or numerous changes at any spot in the menu. Do not use ''~-ENTER-~'' to move between lines. * TAB completion is available, which is useful in entering kernel and ''initrd'' entries. * After starting to type the kernel or initrd name, press TAB. * If additional characters are not added, look at the bottom of the menu as there may be multiple choices. Add characters until only one entry is visible at the bottom, then TAB again. * When editing is complete: * '''CTRL-x''' or '''F10''' - boot with the changed settings (highlighted for emphasis). * '''CTRL-c''' or F2 - jump to the command line to perform diagnostics, load modules, change settings, etc. * If an edit is incomplete and GRUB 2 detects an error in the kernel or ''initrd'' line it will return to the line when exiting this mode. * '''ESC''' - Discard all changes and return to the main menu. * The choices are listed at the bottom of the screen as a reminder. * Edits made to the menu in this manner are non-persistent. They remain in effect only for the current boot. * Once successfully booted, the changes can be made permanent by editing the appropriate file, saving the file, and running `update-grub` as 'root'. == Menu Editing Examples == * Change a kernel version if one is available but not listed on the GRUB 2 menu. * Use the TAB key after entering part of the kernel or ''initrd'' version to see which ones are available. * Add or remove kernel options from the ''linux'' line. * Remove ''quiet'' to display system messages during boot. * Remove existing options and add ''nomodeset'' to avoid module loading, especially if having video issues. * Boot to the recovery mode even if it is not listed on the menu. * Remove existing kernel options from the ''linux'' line and add ''single'' * Remove references to UUIDs * Remove the entire ''search'' line * On the ''linux'' line, replace "root=UUID=" with "root=/dev/sdXY" = Post Boot Follow Up = Any changes made from the GRUB 2 terminal are not permanent. After successfully booting into the system the user must take several steps to ensure the problem is permanently fixed. 1. Update the GRUB 2 configuration file {{{ sudo update-grub }}} 1. Reinstall GRUB 2 to the ''drive's'' MBR or equivalent * Install to the '''drive''', not to the partition. Example: '''''sda''''', not ''sda1'' {{{ sudo grub-install /dev/sdX }}} 1. Inspect the GRUB 2 configuration file. The default is ''/boot/grub/grub.cfg'' * For problems with booting the main linux kernel, verify the ''search, linux'', and ''initrd'' lines in the [### BEGIN /etc/grub.d/10_linux ###] section of the file. * Ensure the paths and kernel/initrd image versions are correct. * Confirm the UUID numbers. * UUIDs can be checked with the `sudo blkid` command. 1. Verify the existence and contents of the system boot folders. * ''/'' should contain the symlinks ''vmlinuz'' and ''initrd.img'' * ''/boot/'' should contain the actual kernel (vmlinuz-X.X.X-XX...) and initrd image (initrd.img-X.X.X-XX...) * ''/boot/grub'' should contain ''grub.cfg'' and numerous module files (*.mod) For a corrupted GRUB 2 installation, purging and reinstalling GRUB 2 is very easy if the user has a working Internet connection. Refer to [[https://help.ubuntu.com/community/Grub2/Installing#Purging_.26_Reinstalling_GRUB_2|Grub2/Installing#Purging & Reinstalling GRUB 2]] for guidance. = Fallback mode = It is possible to configure Grub2 to fall back to a known good menu-entry if the default menu-entry for some reason fails to boot. An example script that can be used for this is available at [[http://wiki.ubuntuusers.de/GRUB_2/Skripte#Fallback-Skript| this webpage]] (in German). = GRUB 2 Errors = GRUB 2 does not report error numbers. If a number is associated with an error, it is a problem with the transition from GRUB legacy to GRUB 2. A GRUB 2 error will leave the user at the '''grub>''' or '''grub rescue>''' prompt, the word '''GRUB''' with no cursor, or a hung boot caused by improper system path designations or a corrupted operating system. These issues are addressed earlier on this page - go to the [[#General Troubleshooting Preparation|General Troubleshooting Preparation]] section to start the recovery process. == Selected Problems and Bugs == === External Drive Installs and ''grub-pc'' Updates === [[https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/496435|Launchpad Bug 496435]] Installs of Ubuntu on external drives can cause problems as ''grub-install'' uses device names (e.g. sda, sdb) rather than UUIDs in certain circumstances. If connected to another machine when an update of grub-pc is made, the upgrade may be written to the incorrect device and make the computer unbootable. A workaround is posted on the bug link above. === External Drive Installs and MBR Selection === [[https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/414996|Launchpad Bug 414996]] When installing Ubuntu to a USB drive, the potential exists for GRUB 2 to write to the hard drive's MBR or split the installation between the hard drive and the USB drive (rather than completely on the USB device). This can render the main drive unbootable. Workaround: During the final stages of the install there is an "Advanced" button which allows the user to select the install location. See the bug report for more details. === Boot Partition is in Logical Volume whose Volume Group contains a snapshot === [[https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/563895|Launchpad Bug 563895]] When your boot partition (the one providing ''/boot'') is a LV, make sure not to have any LVM snapshots inside the containing VG. At reboot this will render your system '''unbootable''', dropping you in a "''grub rescue>''"-shell with the following message: "''error: no such disk.''" The grub-rescue-shell provided does not help you, because all modules (esp. lvm) are unreachable. You'll have to boot from a install medium and remove all snapshots that are in the same VG as your boot partition by hand. This issue is extremely annoying if your server is in a remote datacenter since the origin of the problem cannot be spotted easily and repairing the system may be hard. While this will be fixed in the upcoming Maverick Meerkat 10.10 release, the current Lucid Lynx LTS 10.04 is affected. A workaround would be to install ubuntu using a separated non-LVM partition for ''/boot'' if you are using LVM snapshots regularly. There's some kind of irony that if you're careful and take a LVM snapshot before upgrading (and possibly rebooting) your system, this will trigger the bug. === insmod fails with "error: no such disk" === Several grub2 modules, such as the ''linux''-module depends on other modules, which is attempted to be auto-loaded. For this to work, the variable ''$prefix'', must be set to where the grub2 modules can be found. Usually, this is accomplished with the command "''set prefix=/boot/grub''". = Links = [[https://help.ubuntu.com/community/Grub2|Grub2]] [[https://help.ubuntu.com/community/Grub2/Installing|Grub2/Displays]] [[https://help.ubuntu.com/community/Grub2/Installing|Grub2/Installing]] [[https://help.ubuntu.com/community/Grub2/Submenus|Grub2/Submenus]] [[https://help.ubuntu.com/community/Grub2/Upgrading|Grub2/Upgrading]] [[https://help.ubuntu.com/community/Boot-Repair|Boot-Repair]] ---- CategoryBootAndPartition