Initramfs (wikipedia) is a temporary filesystem that can boot a Linux system. Using initramfs allows you to use complex file partition schemes for your root directory, such as storing your root on a raid array, or on an encrypted partition.
Because it is designed to do such complex tasks, it allows for a number of utilities to be installed, including a basic shell (Busybox), and an ssh server (dropbox).
In some cases, this may mean that you need to be able to set a static IP address for initramfs; for instance this would allow you to remotely decrypt an encrypted root partition.
Doing this is as simple as editing a file, and then running some commands.
Do all of the following with either sudo, or as root.
This is from Debian, but by finding the corresponding file in your distribution, you should be able to replicate the effect.
Editing the Configuration File
First, open the file
Find the line
Underneath it, add a line in this format
Where ipaddress is your desired IP address, the gateway is the IP address of your router (Finding the gateway), netmask is your netmask (almost certainly 255.255.255.0), hostname is the name of the computer, and eth# is the name of the ethernet adapter you wish to use.
Updating the initramfs Image
In order to make the change in IP address effective, you must update the initramfs image.
To do this, run the following command
Once this command completes, you should be able to reboot, and see that the changes have taken effect. If not, try updating grub. Assuming you are running Grub 2, simply run the command