Mandriva 2008 spring : HOWTO compress /usr

Here is a short howto compress the /usr directory in order to save space on your EEE SSD. The /usr directory is the bigest directory. You can save more than 1GB out of the 4GB available.

Introduction

Here is a short howto to compress your /usr directory in order to save more than 1Gb. On my EEE, my /usr folder was 2.3Gb and it’s now compressed to 900Mb leaving 2Gb free on the SSD. I made this tutorial especially for the EEE but it should work with any PC running mandriva 2008.1.

I assume that you already have a running and stable mandriva 2008.1 with mksquashfs tools installed and all the software you need on your EEE.

The compressed /usr is made of two elements : a compressed read only directory with squashfs combined with a writable unionfs. Any change to the /usr will be stored uncompressed in the unionfs filesystem.

You need a USB hard-drive to compress the /usr.
Log in as the super user et mount your USB disk on /mnt

Save/restore your SSD

Before going any further, you should make a full backup of the whole SSD.

This command can do the job :

# dd if=/dev/sda of=/mnt/sav_eee bs=64k

If anything goes wrong, you can restore your previous state with the following command :

# dd if=/mnt/sav_eee of=/dev/sda bs=64k

Create the compressed /usr

Compress the /usr with mksquashfs :

# cd /usr
# mksquashfs * /mnt/usr.sqfs

Create the following mount points :

Here is a short howto to compress your /usr directory in order to save more than 1Gb. On my EEE, my /usr folder was 2.3Gb and it’s now compressed to 900Mb leaving 2Gb free on the SSD.

I assume that you already have a running mandriva 2008.1 with mksquashfs tools installed.

You need a USB hard-drive to compress the /usr.

Log in as the super user et mount your USB disk on /mnt

Compress the /usr with mksquashfs :

# cd /usr
# mksquashfs * /mnt/usr.sqfs

Create the following mount points :

# mkdir /usr.sq /usr.un

Download this tgz and extract it at the root of the filesystem :

# cd /
# tar xvfz scripts_compressed_usr_2008.1.tgz

This tgz contains these system files : functions, halt and rc.sysinit modified in order to handle the compressed /usr.

Time now to remove the /usr…

# init 1
# rm -rf /usr
# mkdir /usr

Finally copy the compressed usr.sqfs at the root of the filesystem :

# cp /mnt/usr.sqfs /

In order to be sure that it’s ok, try the following commands :

# modprobe loop
# modprobe squashfs
# modprobe unionfs
# mount -o loop -t squashfs /usr.sqfs /usr.sq
# mount -o dirs=/usr.un=rw:/usr.sq=ro -t unionfs unionfs /usr

You should have your files in the /usr… Overwise, something went wrong.

BEWARE : Some system updates can crunch the “functions, halt and rc.sysinit” files. You should keep a copy of these files and check them after any upgrade.

Maintaining the compressed /usr

If your /usr.un directory is full of new files, you can move them to a new compressed /usr.

Create the /mnt/usr.sqfs with the earlier commands:

# cd /usr
# mksquashfs * /mnt/usr.sqfs

Switch to runlevel 1 and unmount the /usr :

# init 1
# umount /usr
# umount /usr.sq

Remove any files in the /usr.un directory :

# cd /usr
# rm -rf *

Replace the /usr.sqfs file with the newly created one.

# cp /mnt/usr.sqfs /

Mount the compressed /usr :
# mount -o loop -t squashfs /usr.sqfs /usr.sq
# mount -o dirs=/usr.un=rw:/usr.sq=ro -t unionfs unionfs /usr

Switch to runlevel 5

# init 5