Setup Raspberry Pi with Arch Linux

Source

Author: akeil
Date: 2013-12-28
Version: 2
Updated: 2014-06-09

Note

2014-06-09: Added instructions on how to Change Partition Size.

This post describes how to install and set up Arch Linux ARM [1] on a Raspberry Pi [2] (a Model B Rev 2.0, precisely). This is done by writing the bootable Arch Linux ARM image onto an SD card, then booting the Raspberry Pi with that card. The Pi needs to be connected to the network only, it does not require a monitor or a keyboard.

Requires a PC with a card reader and internet access plus a SD card with at least 2GB storage and finally router that supports DHCP.

ArchLinux is a Linux distribution aimed at simplicity and flexibility. It has a certain "do-it-yourself-style", meaning that most things are not pre-installed or preconfigured. Luckily the Arch Wiki [3] has excellent documentation on most topics.

Prepare the Image

Download the image from the download URL listed at the Arch Linux ARM for Raspberry Pi [4] page.

After the files have downloaded, compare the output of md5sum with the downloaded checksum to verify the integrity of the file. If everything is OK, unzip the image. The ZIP-archive and the md5 checksum are now longer needed and can be deleted.

$ wget http://archlinuxarm.org/os/ArchLinuxARM-rpi-latest.zip
$ wget http://archlinuxarm.org/os/ArchLinuxARM-rpi-latest.zip.md5
$ md5sum ArchLinuxARM-rpi-latest.zip
$ cat ArchLinuxARM-rpi-latest.zip.md5
$ unzip ArchLinuxARM-rpi-latest.zip
$ rm ArchLinuxARM-rpi-latest.zip
$ rm ArchLinuxARM-rpi-latest.zip.md5

This should leave a single file named archlinux-hf-YYYY-MM-DD.img with about 2GB in size. This file goes onto the SD card.

Insert the SD card into the PC's card reader.

Unmount Removable Media

Some systems will automatically mount removable media as soon as they are inserted. If this is the case, unmount it first.

To check if and where a removable media was automatically mounted use lsblk which lists available block devices and their mount points. The last lines should show the SD card and where it is mounted.

You can also use mount to list all mounted partitions.

Use unmount MOUNTPOINT to unmount (might require root permissions).

lsblk should then show the device and its partitions but no mount points. the output looks like this (some lines omitted):

NAME                  MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
[...]
sdc                     8:32   1   3.7G  0 disk
├─sdc1                  8:33   1    90M  0 part
└─sdc2                  8:34   1   3.6G  0 part
[...]

After making sure that the device is not mounted, use dd to write the image to the SD card (as root):

Warning

dd will overwrite any content on the SD card.

# dd bs=1M if=/the/image.img of=/dev/sdX
# sync

/dev/sdX is the device name of the card (for example /dev/sdc). The command will not generate any output until it completes, which may take a while.

The sync command flushes the file system buffers. Run it to make sure that the data is completely written before the SD card is removed.

Change Partition Size

The image comes with a predefined partition size of about 1.7 GB for the main partition. Depending on how many additional packages you are going to install, this can turn out to be a bit low.

Although the partition can be resized while the system is running (see this forum post [8]), it is safer to do it right after writing the image onto the SD card and before inserting the card into the Raspberry Pi.

From this blog post [9]:

# fdisk /dev/sdX
  1. Press p to print the current partition table.
  2. Press d to delete a partition.
    • Delete partition 2.
  3. Press n to create a new partition
    • e to select the "extended" partition type
    • <enter> to accept the suggested partition number (should be "2").
    • <enter> to confirm the offset for the first sector
    • <enter> to confirm the offset last sector
  4. Press n to create another partition
    • l for a "logical" partition (partition number is assigned automatically and should be "5").
    • <enter> to confirm the offset for the first sector
    • <enter> to confirm the offset last sector
  5. Press w to write the partition table

The complete session will look like this:

Command (m for help): p

Disk /dev/sdc: 3965 MB, 3965190144 bytes
122 heads, 62 sectors/track, 1023 cylinders, total 7744512 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: 0x417ee54b

Device    Boot      Start         End      Blocks   Id  System
/dev/sdc1            2048      186367       92160    c  W95 FAT32 (LBA)
/dev/sdc2          186368     3667967     1740800    5  Extended
/dev/sdc5          188416     3667967     1739776   83  Linux

Command (m for help): d
Partition number (1-5): 2

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): e
Partition number (1-4, default 2):
Using default value 2
First sector (186368-7744511, default 186368):
Using default value 186368
Last sector, +sectors or +size{K,M,G} (186368-7744511, default 7744511):
Using default value 7744511

Command (m for help): n
Partition type:
   p   primary (1 primary, 1 extended, 2 free)
   l   logical (numbered from 5)
Select (default p): l
Adding logical partition 5
First sector (188416-7744511, default 188416):
Using default value 188416
Last sector, +sectors or +size{K,M,G} (188416-7744511, default 7744511):
Using default value 7744511

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

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

Then, resize the partition with:

# e2fsck -f /dev/sdX5
# resize2fs /dev/sdX5

The resized partitions should look like this:

$ lsblk
NAME                  MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
[...]
sdc                     8:32   1   3.7G  0 disk
├─sdc1                  8:33   1    90M  0 part
├─sdc2                  8:34   1     1K  0 part
└─sdc5                  8:37   1   3.6G  0 part
[...]

Install

Insert the SD card and connect the Raspberry Pi via Ethernet to your router and power it up.

See if it boots.

Booting takes some time (LED's blinking). When complete, all status LED's should be on except the ACT.

The Raspberry Pi status LED'S:

Label Color Meaning
ACT Green SD Card Access
PWR Red Power
FDX Green Full Duplex LAN connected
LNK Green Link/Activity (LAN)
100 Yellow 100Mbit LAN connected

Luckily, the Arch Linux ARM image for the Raspberry Pi comes preconfigured to start sshd on boot and allow root-login via SSH.

It also supports DHCP [5] which means that if your router has DHCP enabled, the Raspberry Pi will automatically obtain an IP address from the router.

To find out which IP was assigned, either ask your router or guess (guessing is actually not that bad - most routers will follow some semi-predictable pattern when handing out IP addresses).

Log in via ssh:

$ ssh root@ip-of-your-pi

The initial password for the root user is "root", without the quotes.

Post Installation

The Arch Linux beginners guide [6] is also applicable to Arch Linux ARM and describes many standard tasks.

Upgrade

The image file will be fairly up-to-date, but updating doesn't hurt, so:

# pacman -Syu

Some Small Details

Set the hostname

Although the default alarmpi is pretty cool, you can change the hostname to whatever you like:

# echo my-pretty-pi > /etc/hostname

Time Settings

To change or set the local time zone:

# rm /etc/localtime
# ln -s /usr/share/zoneinfo/Europe/Berlin /etc/localtime

Run the date command to print the current local time.

The Raspberry Pi has no Real Time Clock (RTC) which means it will lose its time setting as soon as the power goes off. If it is always (or most of the time) connected to the internet, consider using NTPd [7] to obtain the current time. NTPd is already installed and just needs to be enabled:

# systemctl enable ntpd
# systemctl start ntpd

(enable to always start on boot, start to start right now)

Passwords and Users

To change the password for the root user, just type:

# passwd

This Will open a prompt where you enter your new root password (2x).

The root user should not be used for non-administrative tasks. So add a user for yourself and give it a password:

# useradd -m -s /bin/bash username
# passwd username

The -m option will create a home directory for the new user in /home/username. A group with the same name will also be created if USERGROUPS_ENAB is set to "yes" in /etc/login.defs (which it is).

Configure SSH

If you plan to log in to the Raspberry Pi frequently via SSH, you can make your life easier.

SSHD

Edit /etc/ssh/sshd_config to contain the following lines:

# /etc/ssh/sshd_config
PermitRootLogin no
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile  %h/.ssh/authorized_keys
AllowUsers  your-username

Then restart sshd:

# systemctl restart sshd

You can easily check if everything worked out - if you cannot login via SSH anymore, it didn't.

Also, journalctl --unit sshd will list log messages related to SSH - for example denied login attempts.

Authenticate Without a Password

To log yourself in without a password, generate a key for yourself (on your PC, not on the Raspberry Pi):

$ ssh-keygen -t rsa -b 2048 -f ~/.ssh/name-of-keyfile

Will create two files name-of-keyfile (the Private Key) and name-of-keyfile.pub (the Public Key) in the ~./ssh directory. The .pub file goes onto the Raspberry Pi.

Configure the SSH client to use your keyfile automatically:

$ touch ~/.ssh/config
$ chmod 600 ~/.ssh/config
$ nano ~/.ssh/config

Add the following entry to the config file:

Host rpi-address
    IdentityFile ~/.ssh/name-of-keyfile
    User username

Where "rpi-address" is the IP address of your Raspberry Pi and username is your remote username (on the Pi).

Transfer the keyfile to the Raspberry Pi:

$ scp ~/.ssh/name-of-keyfile.pub username@rpi-address:~

Switch to the Raspberry Pi to install the key:

# su username
$ mkdir ~/.ssh
$ touch ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
$ cat ~/name-of-keyfile.pub >> ~/.ssh/authorized_keys
$ rm name-of-keyfile.pub
$ exit

You should now be able to use type ssh rpi-address and be logged in on the Raspberry Pi.

[1] http://archlinuxarm.org/
[2] http://www.raspberrypi.org/
[3] https://wiki.archlinux.org/index.php
[4] http://archlinuxarm.org/platforms/armv6/raspberry-pi
[5] https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol
[6] https://wiki.archlinux.org/index.php/Beginners%27_Guide
[7] https://wiki.archlinux.org/index.php/Network_Time_Protocol_daemon
[8] http://archlinuxarm.org/forum/viewtopic.php?f=31&t=3119#p18160
[9] http://gleenders.blogspot.de/2014/03/raspberry-pi-resizing-sd-card-root.html