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vladbabii / raspberry_os_buster_read_only_fs

Read only filesystem for Raspberry PI OS - Buster

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Read only filesystem for Raspberry PI OS - Buster

This works on Buster releases of raspberry pi - tested on a PI 4 with a fresh install of the lite version

Initial setup

  • write image file
  • create a file named "ssh" on /boot partition
  • for wifi, creata a file "wpa_supplicant.conf" on /boot and fill in country code ( US, DE, etc) and your wifi name (ssid) and password
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=<Insert 2 letter ISO 3166-1 country code here>

network={
 ssid="<Name of your wireless LAN>"
 psk="<Password for your wireless LAN>"
}

First boot

Run raspi-config and configure everything as you want to

  • memory split
  • localisation
  • time zone
  • ... then reboot

Second boot

Update packages

apt-get update
apt-get upgrade

Run as root

apt-get remove --purge triggerhappy logrotate dphys-swapfile
apt-get autoremove --purge

Edit /boot/cmdline.txt and add at the end of the file

fastboot noswap ro

Log manager change (as root)

apt-get install busybox-syslogd
apt-get remove --purge rsyslog

Edit /etc/fstab and add the ",ro" flags to all block devices that start with PARTUUID=...

proc                  /proc     proc    defaults             0     0
PARTUUID=fb0d460e-01  /boot     vfat    defaults,ro          0     2
PARTUUID=fb0d460e-02  /         ext4    defaults,noatime,ro  0     1

Edit /etc/fstab and add tmpfs

tmpfs        /tmp            tmpfs   nosuid,nodev         0       0
tmpfs        /var/log        tmpfs   nosuid,nodev         0       0
tmpfs        /var/tmp        tmpfs   nosuid,nodev         0       0

Move files

rm -rf /var/lib/dhcp /var/lib/dhcpcd5 /var/spool /etc/resolv.conf
ln -s /tmp /var/lib/dhcp
ln -s /tmp /var/lib/dhcpcd5
ln -s /tmp /var/spool
touch /tmp/dhcpcd.resolv.conf
ln -s /tmp/dhcpcd.resolv.conf /etc/resolv.conf

System random seed

rm /var/lib/systemd/random-seed
ln -s /tmp/random-seed /var/lib/systemd/random-seed

Edit /lib/systemd/system/systemd-random-seed.service , add line

ExecStartPre=/bin/echo "" >/tmp/random-seed

under [Service] section like this

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStartPre=/bin/echo "" >/tmp/random-seed
ExecStart=/lib/systemd/systemd-random-seed load
ExecStop=/lib/systemd/systemd-random-seed save
TimeoutSec=30s

Edit /etc/bash.bashrc and add the lines at the end of the file

set_bash_prompt() {
    fs_mode=$(mount | sed -n -e "s/^\/dev\/.* on \/ .*(\(r[w|o]\).*/\1/p")
    PS1='\[\033[01;32m\]\u@\h${fs_mode:+($fs_mode)}\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
}
alias ro='sudo mount -o remount,ro / ; sudo mount -o remount,ro /boot'
alias rw='sudo mount -o remount,rw / ; sudo mount -o remount,rw /boot'
PROMPT_COMMAND=set_bash_prompt

Create /etc/bash.bash_logout

mount -o remount,ro /
mount -o remount,ro /boot

Reboot and enjoy!

How to use

Connect via ssh and type "rw" to make the filesystem writable again and install anything you want.

Type "ro" to make the filesystem readonly again - it can take some time untill all writes are finished so be a little patient.

The prompt will change based on rw or ro filesystem to let you know the state, here is how it will look like when switching from ro to rw and back again

pi@raspberrypi(ro):~$ rw
pi@raspberrypi(rw):~$ ro
pi@raspberrypi(ro):~$

Sources

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Read only filesystem for Raspberry PI OS - Buster