So, I have separate partitions for /var and for / and I've decided that my /var partition is big enough to also hold /tmp. Can I mount both directories to that partition or do I have to split it up?
Splitting it would suck because they are both so VARiable and TEMPorary.
So you mean, how can you have both /var and /tmp on a single external partition?
Here are your options.
Boot from another system (e.g. a LiveCD) and mount your /var partition and do this as root:
cd /mnt/var mkdir -m755 .newvar mv * .newvar # won't try to move .newvar because it begins with a period mv .newvar var # rename .newvar to var mkdir -m1777 tmp # make a tmp dir
Now you'll have to specify in your /etc/fstab:
1. a mount point for the whole partition, e.g., /mnt/ignore_me
2. the following two lines:
/mnt/ignore_me/var /var none bind /mnt/ignore_me/tmp /tmp none bind
Keep mounting the /var partition as you are currently, but do this as root:
cd /var mkdir -m1777 .tmpdir # make a hidden /var/.tmpdir --- notice that /var/tmp is something different
Add the following to your /etc/fstab, after the lines that mount /var:
/var/.tmpdir /tmp none bind
In either case, the directories that you "bind"-ed to another mount point will also still be available at their original locations. With the "mount" command, there's also a different option to move the directory (-o move instead of -o bind). But last time I checked, you couldn't specify "move" in an fstab file. Only bind.