How to boot from RAM on debian

boot-from-ram-debian.md

Booting Debian from a RAM disk

This guide is adapted from http://reboot.pro/topic/14547-linux-load-your-root-partition-to-ram-and-boot-it/

What you need:

• lots of RAM
• Debian based distribution or any that supports booting from initramfs
• mkinitramfs or a tool to build a new initramfs
• some linux knowledge
• no need to create an image
• no need for Grub4Dos
• no need for a "special driver"

Step 1: Choose a distribution thats supports booting from initramfs. (like ubuntu)

Step 2: Install to harddisk. Make sure you split it into multiple partitions (/, /boot, /home, swap, ...).

Step 3: Boot your new system, install updates, drivers if neccessary (this will improve performance), strip it down to the minimum. Every file will be loaded to RAM ! A fresh install uses about 2 GB auf harddisk-space.

Step 4: modify /etc/fstab :

cp /etc/fstab /etc/fstab.bak find the line specifing the root partition and change it in: none / tmpfs defaults 0 0* save

Step 5: edit the local script in your initramfs: cd /usr/share/initramfs-tools/scripts/* make a backup of /usr/share/initramfs-tools/scripts/local cp local local.bak* modify local, find this line:

# FIXME This has no error checking

# Mount root

mount ${roflag} -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} ${rootmnt}

change it to:

# FIXME This has no error checking

# Mount root

#mount ${roflag} -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} ${rootmnt}

mkdir /ramboottmp

mount ${roflag} -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} /ramboottmp

mount -t tmpfs -o size=100% none ${rootmnt}

cd ${rootmnt}

cp -rfa /ramboottmp/* ${rootmnt}

umount /ramboottmp

• save
• execute, or rebuild initramfs mkinitramfs -o /boot/initrd.img-ramboot* replace modified local with original file cp -f local.bak localStep 6:
• modify this file (needs a better solution) /boot/grub/grub.cfg* copy the first boot entry and replace the /initrd line with this: /initrd /boot/initrd.img-ramboot* label the new entry as RAMBOOT This will boot our generated initramfs instead the original one. Step 7:
• reboot
• choose standart boot (no ramdisk)
• choose RAMBOOT and all your files on the root partition will be loaded to a tmpfs

As I am about to try this, may I ask if I got it right:

We modify /usr/share/initramfs-tools/scripts/local so that the initramfs will mount a tmpfs as / and copy the content of the original rootfs there. Then we restore the original script and any initramfs built after that won't be special any more.

So we do have to repeat Step 5 (and maybe 6) after every kernel update, don't we?

In Step 7 we boot with an unmodified initramfs. Will this even work since we modified the fstab to have a tmpfs as / in Step 4?