RAMboot How-To for Debian 8 Jessie

I have refined and updated my RAMboot how-to for Debian 8. Honestly, my previous how-to's still work fine for Debian 8, regardless of the switch to systemd. I have, however, tightened things up.

The basic concept is to boot from a local hard drive or USB drive, using a modified initrd to unpack ramboot/image.tar.gz to a tmpfs ramdisk. From then on, the system runs entirely from ram - uncompressed. This is like running off an extremely fast SSD, but with some important differences:

1) Because tmpfs is purely in RAM, you lose all data on power down. A script can save the current / partition into an updated ramboot/image.tar.gz, but this is a bit slow. See addendum2 for a very fast way to save just your home directory on demand.

2) Boot time is slow due to the need to load the entire image.tar.gz file. A normal SSD just mounts and immediately continues with the boot process.

3) Because the OS partition resides entirely in RAM, less RAM is available for normal use. However, this can be compensated for by using a swapfile or partition. This swapfile may be on another computer, and may even be put on the RAM of another computer (see below).

4) Because / is not a "normal" partition, update-grub will fail when it tries to figure out the canonical path of /. To compensate, we'll rename /boot/grub/grub.cfg so kernel updates do not even attempt to run update-grub. You'll have to manually copy over updated initrd and vmlinuz files to the physical boot drive.

So why RAMboot? If you've got enough RAM, it is blazing fast compared to a normal hard drive, or a slower SSD. Combined with swap on a fast SSD, it will give you the fastest performance you can squeeze out of your computer - if you don't mind the extra boot time.

Also, it costs less to not buy an SSD, and there are situations where an SSD is not a practical option. For example, you might have a laptop with only one drive bay, and you want a spinning hard drive with lots of storage in it. Or you have a Mac Mini where the hardware is purposefully designed to make it difficult to replace the hard drive.

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Step 1) MINIMAL DEBIAN 8 INSTALL

Do a minimal Debian 8 install on /dev/sda1 (either a hard drive or USB, typically) and boot to it. Deselect all software suites, unless you're sure you want them.

Step 2) CREATE /tmp RAMDISK, PREPARE /etc/fstab

Log in as root. Edit /etc/fstab and add these lines:

The resulting fstab will look like:

Make a couple copies with:

Edit /etc/fstab.RAMBOOT to uncomment the last line and modify the old / to /mnt/sda1. The result will look like:

Now, make /ramboot, /mnt/sda1 and mount /tmp with:

Step 3) PREPARE CUSTOMIZED /usr/share/initramfs-tools/scripts/local

Make a copies of /usr/share/initramfs-tools/scripts/local with:

Edit local.RAMBOOT by replacing the root mount line from this:

to this:

Step 4) CREATE CUSTOM BOOT FILES


Step 5) CREATE THE IMAGE

We're going to temporarily move the RAMBOOT files in place of the NORMAL files, and also temporarily move grub.cfg. The reason for moving grub.cfg is to prevent the ramboot system from attempting to run update-grub on kernel updates (it would fail, because it can't find the canonical path of /). Later on, you will have to manually copy over the updated vmlinuz and initrd.img files to /mnt/sda1/boot/vmlinuz-ramboot and initrd.img-ramboot.

Reboot, and see if it works! Choose "advanced options" to choose between ramboot and normal mode.

At this point, the / folder will have about 571MB used, and image.tar.gz will be about 220MB in size.

MAINTENANCE

When you want to save a new image, based on the current state, do the following:

If the kernal has been upgraded, manually copy over the new initrd.img and vmlinuz with something like:

To move this RAMBOOT option to another computer/drive that already has a normal install, simply copy over initrd.img-ramboot and vmlinuz-ramboot to the /boot/ and image.tar.gz to /ramboot/ (create /ramboot). Then run "update-grub" and it should detect the new ramboot option. Remember to go into "advanced options" on boot, to choose between ramboot and normal mode.

INSTALLING XFCE4 GUI

Here's an example for installing a GUI. It's not the most stripped down option, but it's easy to specify without being too heavyweight.

After this, / will be about 1084MB and image.tar.gz will be about 428MB. Obviously, adding more software will increase the size of both.

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ADDENDUM - USING RAM ON ANOTHER COMPUTER FOR SWAP

RAMboot consumes a good chunk of RAM, but less used files may be offloaded to swap. Thus, RAMboot can greatly benefit from fast swap space. If you've got a local SSD, great! Put a swap partition or swapfile on it, and you can practically eliminate the RAM penalty of RAMboot.

But what if you don't have an SSD? If you have a gigabit ethernet connection, you can use another computer's RAM as a pretty fast swap space. The basic idea is to set up the other computer as an nfs server, serving up a swapfile within a tmpfs nfs share. I detail how to do this in another blog post here:

http://www.linuxquestions.org/questi...omputer-37197/

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ADDENDUM2 - "PERSISTENT" HOME ON DISK

One problem with RAMboot is that the snapshot process takes several minutes. This is okay for periodic software updates and the occasional configuration change. But it's annoying for /home, which may update frequently. To account for this, you can set up a taskbar icon to run a save script, along with a script in /etc/rc.local to load /home.

Example script /home/kuo/hsave.sh
You can add a load script to /etc/rc.local, making the end of it look something like this:
This may cause odd behavior if you have auto-login, as the login process fights with this script running like crazy. Thus, you might want to set auto-login to have a bit of a time delay.