Remount a readonly filesystem to rw

When you want to remount a filesystem read/write because of a hardware failure or other failures, enter the following:

sudo mount -o remount,rw /partition/identifier /mount/point

Where the /partition/identifier the actual path is to the device, for example: /dev/sda2

When this fails, a system reboot can also fix readonly filesystems.

Of course you need to find out why the filesystem became readonly. Most of the time you can find this information in the dmesg.