GRUB is a small program that is used to manage booting into multiple operating systems and to specify boot options for each of the operating system. GRUB could get corrupted or deleted in events like when installing Microsoft Windows, making you unable to load your other installed operating systems.
GRUB configuration is stored in other partition such as in your Ubuntu installation disk. This means if GRUB itself is corrupted or deleted, it can be re-installed and configured to read from existing configuration files.
For Ubuntu installer, click on the Try Ubuntu button.
If no Live CD mode available, press <ctrl> + <alt> + <f2> keys to get to the terminal. For Ubuntu, the default username is ubuntu and the password is empty (just press enter at the password prompt).
$ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT loop0 7:0 0 1.9G 1 loop /rofs loop1 7:1 0 89.3M 1 loop /snap/core/6673 loop2 7:2 0 53.7M 1 loop /snap/core18/941 sda 8:0 0 20G 0 disk └─sda1 8:1 0 20G 0 part sr0 11:0 1 2G 0 rom /cdrom
$ mkdir tmp
$ sudo mount /dev/sda1 tmp/
$ sudo mount --bind /dev tmp/dev $ sudo mount --bind /proc tmp/proc
$ sudo chroot tmp/ [email protected]:/#
[email protected]:/# grub-install /dev/sda Installing for i386-pc platform. Unknown device "/dev/sda1": No such device Unknown device "/dev/sda1": No such device Unknown device "/dev/sda1": No such device Unknown device "/dev/sda1": No such device Unknown device "/dev/sda1": No such device Unknown device "/dev/sda1": No such device Installation finished. No error reported.
[email protected]:/# exit exit
$ sudo poweroff
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