Changing OpenElec's /tmp size

OpenElec has a limited /tmp partition. Very limited, i.e. 10MiB. Many things fall over because they need more than this on the occasion - especially if it's not the only thing using the tmpfs.

In order to change this you either have to hack around with automatically-created symlinks in startup scripts, or change it yourself.

The size of the /tmp partition is stored in /etc/init.d/01_mount-filesystem

mount -n -t tmpfs -o size=10m tmpfs /var

The problem is, that file is readonly. The reason it's readonly is that the entire root filesystem is stored in a squashfs partition.

To amend it, it is simply a case of unsquashing it, fixing it, and resquashing it.

Fix it

Pull the SD card out of your RPi (I'm assuming that's where you have it) and put it into your card reader. Let your system mount it.

You should have a SYSTEM drive somewhere on your computer. Lubuntu mounts it at /media/altreus/SYSTEM, so let's go with that.

$ mkdir squash
$ cd squash
$ cp /media/altreus/SYSTEM/SYSTEM SYSTEM.bak
$ unsquashfs SYSTEM.bak

Now we have a copy of the OpenElec root filesystem in a .bak file so we can undo it when we screw it up later. We also have the files themselves unpacked into squashfs-root. This is the default place unsquashfs puts them.

$ vi squashfs-root/etc/init.d/01_mount-filesystem

Change the file to have a better size /tmp. I used 500mb because my SD card is 8GB. Ignore the first instance of tmpfs in the file; we want to change the 10mb one.

$ sudo mksquashfs ./squashfs-root SYSTEM

It's important that you do this with sudo. The file /etc/shadow has permissions 000, making it only accessible by root. This is how we got it when we unsquashed it, so this is how we want to keep it. My /etc/shadow is 600, but they presumably wanted theirs to be 000. If we want to do the above step without root, we'd have to change the permissions so our user can see it - we can't change the permissions after it's squashed, so the only way to get a 000 file into the filesystem is to squash it with root.

Anyway, done.

$ cp SYSTEM /media/altreus/SYSTEM

Your new squashfs file will be mounted by OpenElec and your tmpfs will now be mounted with the size you gave it.

I'm not 100% certain this is stable. My Pi has started rebooting occasionally; but I might be giving it more than it can handle. It is an old model, but if I've introduced a bug because 500mb is too much, or something, I'm sure I'll get to the bottom of it and update the post,