early-ssh is a simple initramfs hook, which installs Dropbear SSH server into your initramfs, and starts it at boottime, so you will be able to do a lot of things remotely over SSH, before your root partition gets mounted, for example: * unlocking LUKS encrypted crypto devices - even your root can be an encrypted filesystem * assembling/altering RAID arrays (mdadm) * checking the root filesystem in read-write mode, taking action in case of errors * and so on...