Minimalist Raspberry Pi Server Image

The following tutorial will help you generate a 367MB Raspbian image (uncompressed).

The standard 2012-12-16 version of Raspbian “Wheezy” fills up 1.5GB (or 88%) of a 2GB SD card, which has a formatted capacity of only 1.8GB. While I have a larger capacity SDHC card for this particular RPi (I have five “pies”), one of the projects I’m considering is potentially quite data intensive, so I want to reserve as much disk space as possible.

My previous article began addressing the removal of unnecessary packages but its primary focus was on reducing I/O usage, however this article is focused on conserving disk space and reducing the operating system fingerprint. This optimizes the RPi for a server-type environment, rather than its use as a desktop workstation.

This minimalist image is different from others since it is significantly smaller than most images, yet it retains sound and touch-screen support.

Remove the GUI Modules

Let’s start by getting rid of over 325 optional packages (about 700MB) used by the graphical user interface:

sudo apt-get purge xserver.* x11.* xarchiver xauth xkb-data console-setup xinit lightdm lxde.* python-tk python3-tk scratch gtk.* libgtk.* openbox libxt.* lxpanel gnome.* libqt.* libxcb.* libxfont.* lxmenu.* gvfs.* xdg-.* desktop.* tcl.* shared-mime-info penguinspuzzle omxplayer gsfonts
sudo apt-get --yes autoremove
sudo apt-get upgrade

Remove Development Packages (Optional)

My personal minimalist RPi image retains most of the default installed development packages.

sudo apt-get purge gcc-4\.[0-5].*

However, you can optionally recover almost 150MB of space by removing the majority of compiler and development packages from your image.

sudo apt-get purge `sudo dpkg --get-selections | grep "\-dev" | sed s/install//` gcc-4\.[0-6].* python.*
sudo apt-get --yes autoremove

Disable Memory Swapping

Memory swapping allows part of the usable memory of your computer to be stored on disk, effectively allowing the system to have more RAM than it does physically. Disabling swap files helps free up valuable disk space.

sudo swapoff -a
sudo apt-get purge dphys-swapfile
sudo rm /var/swap

Delete Unnecessary Extras

A few stray files and folders slice up more than 125MB of the Raspberry Pi.

sudo rm -rf /usr/share/doc/* /opt/vc/src/hello_pi/hello_video/test.h264 /home/pi/python_games
find /usr/share/locale/* -maxdepth 0 -type d |grep -v en |xargs sudo rm -rf
find /usr/share/man/* -maxdepth 0 -type d |grep -Pv 'man\d' |xargs sudo rm -rf

Replace SSHd with Dropbear

Dropbear is a lightweight SSH v2 server which lacks backwards compatability support for SSH v1 (translation: smaller code base, uses less memory and fewer resources) and is secure enough for general use — ideal for the Raspberry Pi.

sudo apt-get install dropbear openssh-client
sudo /etc/init.d/ssh stop
sudo sed -i 's/NO_START=1/NO_START=0/' /etc/default/dropbear
sudo /etc/init.d/dropbear restart

After testing that you can still connect to your RPi via SSH, remove the default ssh server.

sudo apt-get purge openssh-server.* openssh-blacklist.*

Eliminate Rarely Used Caches

Prevent aptitude from caching package data by creating /etc/apt/apt.conf.d/02_nocache. This will slow down package updates, but will save about 35MB of disk space in the final image. You could remove the aptitude package altogether, but I find its presence more useful than not, especially when the bulky cache files are removed.

Dir::Cache {
   srcpkgcache "";
   pkgcache "";
}

Since we’re done using apt for package updating, after you reboot your Pi with sudo reboot, you can remove the orphaned cache files to recover another 35MB of disk space:

sudo rm -f /var/cache/apt/*cache.bin
sudo apt-get --yes autoclean
sudo apt-get --yes clean

Prepare for Final Imaging

Numerous files and logs are safely re-created or re-fetched as needed. Removing them will shrink the overall size of the finalized minimalist distro.

sudo find / -type f -name "*-old" |xargs sudo rm -rf
sudo rm -rf /var/backups/* /var/lib/apt/lists/* ~/.bash_history
find /var/log/ -type f |xargs sudo rm -rf
sudo cp /dev/null /etc/resolv.conf

Having also incorporated some drive-I/O-reduction techniques, running df -hlP on my Raspberry Pi shows disk usage of only 367MB, a significant reduction from the original 1.5GB. Your mileage may vary. Shutdown the Raspberry Pi with sudo halt, remove the SD card from the Raspberry Pi board and access it from a Mac or Linux computer to create the final image.

Author’s Note: If you’re just cleaning up your Raspbian installation and have no need to create a distributable image, you can stop now.

To determine which drive designation to use on a Mac, type diskutil list and locate the Identifier of the Linux disk type that ranges around 1.9 GB. On my MacBook Pro, mine is “disk1s2”.

sudo dd if=/dev/disk1s2 of=2012-12-16-wheezy-raspbian-rr-minimalist.img count=3788800

An archive image file is transferred to your Linux PC or Mac, ready for the next steps to generate a zero-byte-filled, compressed final distribution image. Since I’m using a Mac, for which the steps are not very straightforward because the Mac will not natively mount the RPi ext4 partition, I’ll cover that in a future article.

In the meantime, for native Linux users, you can generate a compressed image with the following generic steps.

mkdir mnt
sudo mount -o loop,offset=$((512*122880)) 2012-12-16-wheezy-raspbian-rr-minimalist.img mnt
sudo sfill -z -l -l -f mnt
sudo umount mnt
7z a -t7z -m0=lzma -mx=9 -mfb=64 -md=32m -ms=on 2012-12-16-wheezy-raspbian-rr-minimalist.img.7z 2012-12-16-wheezy-raspbian-rr-minimalist.img

If you’ve gotten this far, congratulations! The original Raspbian installation image uncompressed to 1.5GB, while the minimalist version is well under 600MB — or even sub-400MB, depending on the options chosen. Use your image any way you want in-house, however I wouldn’t start distributing your image quite yet; wait for a future article where we cover the final topics of security and key re-generation. And no one, not even the builders of Raspbian, seems to have properly addressed the licensing concerns of the included non-free hardware drivers.