This tutorial guides you through the process of installing the ARM flavour of Arch Linux in a RaspberryPi. This is a headless installation procedure, no monitor/tv or keyboard are required.

Get Arch Linux ARM

You can download the image using a direct download link or torrent. The latest version available (at this time) is the archlinux-hf-2013-02-11. After downloading the zip archive containing the image verify the SHA-1 checksum. First download the file in the same path as the zip archive and then run:

$ sha1sum -c archlinux-hf-2012-09-18.img.sha1

Install on SD card

The installation process is pretty straighforward. Insert the SD card in your computer and transfer the image to the card using the dd command as root. As always, pay attention to the supplied destination device. Make sure you use the one corresponding to the SD card or you could trash all your data on other devices. Also make sure that the destination device is not mounted. You can use the lsblk command to verity that. We will just use sdX as an example.

# dd bs=1M if=archlinux-hf-2013-02-11.img of=/dev/sdX

Expanding the root partition

After the image transfer is complete two partitions are created. The sdX1 partition will be mounted at /boot and the filesystem is VFAT. The other partition, sdX2 holds the root filesystem and is formatted as ext4.

The root filesystem is a little smaller than 2GB. If the SD card is bigger (it should be) we need to expand this partition to fill the remaining space. Alternatively we could create a second filesystem and mounted at a mount point of our choice. The creation of a new filesystem is really simple, so it is not covered here.

In order to utilize the remaining free space, first we expand the partition and then we expand the filesystem. As always make sure that the partitions are not mounted and that you are altering the proper ones. The following examples assume that the SD card is the device /dev/sdb and the root partition the /dev/sdb2.

Start fdisk. The p command lists the partitions in the device /dev/sdb.

# fdisk -u=sectors /dev/sdb
   Command: p

   Disk /dev/sdb: 7822 MB, 7822376960 bytes
   241 heads, 62 sectors/track, 1022 cylinders, total 15278080 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes
   Disk identifier: 0x000c21e5

   Device Boot      Start         End      Blocks   Id  System
   /dev/sdb1   *        2048      194559       96256    c  W95 FAT32 (LBA)
   /dev/sdb2          194560     3862527     1833984   83  Linux

Then, we delete the the second partition (the roor):

Command (m for help): d 
Partition number (1-4): 2
Partition 2 is deleted

and re-create it. We create the new partition as primary and we set the last sector at the end of the SD card. The default settings should be fine here.

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): p
Partition number (1-4, default 2): 2
First sector (186368-15278079, default 186368): 
Using default value 186368
Last sector, +sectors or +size{K,M,G} (186368-15278079, default 15278079): 
Using default value 15278079
Partition 2 of type Linux and of size 7.2 GiB is set

The partition is already set to Linux (83) so there is no need to alter it. Finally, save the changes:

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

In order to expand the filesystem, first we run the checkdisk program to detect and fix inconsistencies and then use the resize program.

# e2fsck -f /dev/sdb2
# resize2fs /dev/sdb2

IP discovery and remote login

The Arch Linux ARM image has the ssh deamon enabled by default. In order to login we must first determine which IP the rpi has acquired from the local network. This assumes that there is a working DHCP server on the LAN. One way to get the IP address is to check the DHCP logs or the router logs if DHCP is running from a router. As an alternative, we can run a ping scan on the LAN using nmap. Assuming that the lan subnet is with mask run:

# nmap -PE -sn -n

After finding the IP login using the username and password root.

Post-install configuration

After you login, you should change the root password using passwd. Also, it is a good idea to re-generate the rsa and dsa keys.

# ssh-keygen -f /etc/ssh/ssh_host_dsa_key -N "" -t dsa
# ssh-keygen -f /etc/ssh/ssh_host_rsa_key -N "" -t rsa

Answer “yes” on prompt to overwrite. To run a full system upgrade run:

# pacman -Syu

Memory allocation

Depending on the usage you are planning to do with the rpi it might be a good idea to adjust the RAM split between the CPU and the GPU. Edit the file /boot/config.txt file and change the value of the variable gpu_mem_256 or gpu_mem_521 depending on the rpi model you have. This post shows the valid memory values. Note that you must also take into consideration the cma_lwm and cma_hwm variables. These variables allow dynamic memory management at runtime. Make sure that gpu_mem_256 (or 512) value is higher than the high water mark cma_hwm. More info at the links on the bottom of this post.

Sources and further reading