Sometimes if server is shutdown incorrect filesystem filesystem can be corrupted and loaded in “read only” mode.
To check file system status use command:
mount | grep /dev/sd
This command show filesystem status, if filesystem is read only – you will see “ro” status: /dev/sda2 on / type ext4 (ro,readonly,data=ordered)
To fix filesystem use command:
fsck /dev/sda2
This command will fix all errors on filesystem, To apply fix enter y on keybord. When fixing is complete reboot system and check filesystem again.