Mounting root readonly to protect flash in embedded system

[eddy89]

Hi all! I've installed gentoo on an embedded ARM board, all went successfully and works good.
Now, as the root fs stays on a micro SD, i would like to reduce writes as possible.
Actually I don't need to save logs or similar, I just want the system to start every time in the same way.
I thought to edit fstab to mount / readonly, and mount some dirs as tmpfs (the board has 512Mb of ram so it's ok).
The question is: wich directories needs to be writable to start correctly the system?

Thank you.

[NeddySeagoon]

eddy89,

You need to make /etc/mtab a symlink to /proc/mounts to keep mount happy on a read only root.
/tmp needs to be writable
Parts of /var need to be writable too, .e.g. /var/log/... /var/run/... /var/lock/... They can all be in RAM as long as you don't mind throwing away logs at power off.
Exactly what depends on installed programs.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.