Set up Arch Linux ARM on Raspberry Pi to boot from and use a read-only file-system

Read-only FS on Arch Linux ARM.md

Read-only FS on Arch Linux ARM

Unlike your typical computer where you usually shutdown properly, I cannot rely on this during the use of my Raspberry Pi. If the Raspberry Pi is improperly shutdown too many times, data corruption in the file system leading to unbootable SD card may result. So we should use a read-only file system.

Full instructions and explanations are obtained from this link but you can run these commands directly. I modified some of the instructions for personal convenience.

Login with default username: alarm, password: alarm

#Optionally enable root over SSH. The rest of these instructions assume u are in root.
su
nano /etc/ssh/sshd_config
#Add "PermitRootLogin yes" to the Authentication section after "#PermitRootLogin prohibit-password" then save
reboot

#Login as root


#Update everything first, remove cache then reboot to detect problems
pacman -Syu  
# Delete certs if you see a message like "/etc/ssl/certs/ca-certificates.crt exists in filesystem" then rerun pacman -Syu
rm /etc/ssl/certs/ca-certificates.crt
#May be needed if the pacman version has changed during the update
pacman-db-upgrade
#Optional if you want to clear the cache
pacman -Sc
reboot

#Change timezone (optional)
rm /etc/localtime
ln -s /usr/share/zoneinfo/Asia/Singapore /etc/localtime

#Relocate DNS cache (This step causes DNS problems on the latest Arch Linux ARM kernels so skip this)
#rm /etc/resolv.conf
#ln -s /tmp/resolv.conf /etc/resolv.conf

#Adjust /etc/fstab, add/modify to the following hashed lines. Mount certain directories to RAM disk.
nano /etc/fstab
#Add the following lines up to the #end. Include the first commented line in case you have to set to write enabled next time.
#/dev/mmcblk0p1  /boot           vfat    defaults        0       0
/dev/mmcblk0p1  /boot   vfat    defaults,ro,errors=remount-ro        0       0
tmpfs   /var/log    tmpfs   nodev,nosuid    0   0
tmpfs   /var/tmp    tmpfs   nodev,nosuid    0   0
#end

#Adjust journald service to not log the system log to prevent flooding of the /var/log folder
nano /etc/systemd/journald.conf
#Uncomment and set "Storage=none"

#To mount / partition as read-only
nano /boot/cmdline.txt
#Replace the "rw" flag with the "ro" flag right after the root= parameter.

#Disable systemd services
#systemctl disable systemd-readahead-collect #Not working now
systemctl disable systemd-random-seed
#systemctl disable ntpd #Not working now

#Put shortcut shell scripts to re-enable read-write temporarily if needed
printf "mount -o remount,rw /\nmount -o remount,rw /boot" > writeenable.sh
printf "mount -o remount,ro /\nmount -o remount,ro /boot" > readonly.sh
chmod 500 writeenable.sh
chmod 500 readonly.sh

#Change your password if needed (Optional)
"passwd root" or "passwd alarm" 

#Remove history
history -c -w

reboot

To enable read-write temporarily to do say an update, just run ./writeenable.sh.

References

1. Read-only file system

@polmon Thanks for the effort in pointing things out. The issue now is that I'm using the Raspberry Pi only for Bluetooth purposes so I didn't test the internet connectivity problems.

I apologise in advance as I don't have the time right now to troubleshoot the issue.

@polmon: It looks to me like journald has sucked up too much memory. Maybe try to tune journald to forget faster old log entries if space is getting thin.

I might suggest setting the journald.conf to include:
Storage=volatile
This permits you to see what's happened this boot.