I have been tasked with running Linux as an operating system on an embedded device. The target has an x86 processor and has 8 GB CompactFlash device for storage. I have managed to use buildroot to create the kernel image and cross compilation tools. I have partitioned the CF device into a small FAT partition where the kernel image resides as well as syslinux boot configuration and an ext3 file system where I have decompressed the root file system generated by buildroot to. The system boots successfully using syslinux by setting the root directory to the CF ext3 partition where my buildroot file system is located. My question is centred around the need for robustness in the face of immediate (and frequent) power loss as it is crucial for the device to boot successfully after power outages. I have read that mounting the root file system as read only is a way of ensuring data integrity. Is this a sensible way for me to proceed? I have also read about the possibility of loading the root file system into RAM to achieve the same thing but as yet do not know how to do so. Is there a preferred way of achieving this goal and if so what is the best way for me to proceed?
Is using a read only root file system a good idea for embedded setup?
embedded;ram;readonly;root filesystem;buildroot
New answer (2015-03-22)(Note: This answer is simpler than previous, but not more secure. My first answer is stronger because you could keep files read-only by fs mount options before permission flags. So forcing to write a files without permission to write won't work at all.)Yes, under Debian, there is a package: fsprotect (homepage).It use aufs (by default, but could use another unionfs tool) to permit live session changes but in RAM by default, so everything is forgotten at reboot.You could install them by running simply:apt-get install fsprotectOnce done, from online doc:After that:Edit /boot/grub/menu.lst or /etc/default/grub2 or /etc/lilo.conf and add fsprotect=1G to kernel parameters.Modify 1G as needed.Apply changes (i.e. run update-grub)Edit /etc/default/fsprotect if you want to protect filesystems other than /.rebootYou may also want to password protect the grub bootloader or forbid any changes to it. From there, if some file is protected against changes, for sample bychmod ugo-w myfileif you use for sample vi myfile and try to write on it with command :w!, this will work and your  myfile became changed. You may reboot in order to retrieve unmodified myfile.That's not even possible with my following first solution:Old (first) answer:Yes, it is a strong solution, but powerfull!Making r/o useableYou have to mount some directories in rw, like /var, /etc and maybe /home. This could by done using aufs or unionfs. I like this another way, using /dev/shm and mount --bind:cp -a /var /dev/shm/mount --bind /dev/shm/var /varYou could before, move all directories who have not to change in normal operation in a static-var, than create symlinks in /var:mkdir /static-varmkdir /static-var/cachemkdir /static-var/libmv /var/lib/dpkg /static-var/lib/dpkgln -s /static-var/lib/dpkg /var/lib/dpkgmv /var/cache/apt /static-var/cache/aptln -s /static-var/cache/apt /var/cache/apt... # an so onSo when remounting in ro, copying /var in /dev/shm won't take too much space as most files are moved to /static-var and only symlinks are to be copied in ram.The better way to do this finely is to make a full power-cycle, one day of full work and finely run a command like:find / -type f -o -type f -mtime -1So you will see which files needs to be located on read-write partition.LoggingAs in this host no writeable static memory exist, in order to store history and other logs, you have to config a remote syslog server.echo >/etc/syslog.conf '*.* @mySyslogServer.localdomain'In this way, if your system break for any reason, everything before is logged.UpgradingWhen running whith some mount --bind in use, for doing such an upgrade while system is in use (whithout the need of running init 1, for reducing down-time), the simplier way is to re-build a clean root, able to do the upgrade:After remounting '/' in read-write mode:mount -o remount,rw /for mpnt in /{,proc,sys,dev{,/pts}};do    mount --bind $mnpt /$mnt$mpnt;    donechroot /mntapt-get update && apt-get dist-upgradeexitumount /mnt/{dev{/pts,},proc,sys,}syncmount -o remount,ro /And now:shutdown -r now