Ubuntu boot to initramfs

Problem:

Ubuntu cannot boot normally but drop to initramfs. The reason is some part of filesystem is broken, so we need to fix.

BusyBox v1.18.5 (Ubuntu 1:1.18.5-1ubuntu4) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs)

Solution write the command of fsck /dev/sdax like the below and give Y if the console ask for fixing something:

(initramfs) fsck /dev/sda1

or

(initramfs) fsck /dev/sdaX

X specifies mounted disk part number.

If you don't want to manually press 'y' every time it asks for a fix, you can also run the command with the -y option.

(initramfs) fsck /dev/sdaX -y