How to have multiple directories point to the same partition/disk?

General system Kernel, boot, graphics & hardware
1

I have a small ssd on which my system (including home) is installed but would rather have some directories like /var, /tmp, ~/.var use up the space on a partition on my hdd (/dev/sdbX). The first thing I tried was something simple like this:

mount /dev/sdbX /tmp
mount /dev/sdbX /var
mount /dev/sdbX ~/.var

but I noticed that if I create a file in one directory (e.g. touch /var/newfile), then that file appears in the other directory (will that create problems?). The second thing I tried was something like this:

mkdir ~/mount
mount /dev/sdbX ~/mount
mount -o bind ~/mount /var
mount -o bind ~/mount /tmp
mount -o bind ~/mount ~/.var

but I ran into the same ‘problem’ as above. Of course, I could just split /dev/sdbX into multiple partitions but I don’t want to do that because I don’t know exactly how much space these directories will need.

I use btrfs, if that helps.

2

Link, example:

sudo  ln -s /data/Downloads ~/Downloads

But first move the directory to the harddisk :wink:

3

Try this:

mkdir ~/mount
mount /dev/sdbX ~/mount
mkdir ~/mount/var
mkdir ~/mount/tmp
mkdir ~/mount/localvar
mount -o bind ~/mount/var /var
mount -o bind ~/mount/tmp /tmp
mount -o bind ~/mount/localvar ~/.var

Before bind mounting over /var make sure you use rsync to copy all the data over. Mounting over /var will break pacman.

Alternatively, you can replace the bind mounts with symbolic links as suggested by @xircon. The effect will mostly be the same either way.

That being said, their will most likely be a performance hit by moving /tmp to your HDD. I would consider not doing that if I were you.

4

I feel dumb for not thinking of making subdirectories under ~/mount. Silly me. Anyway I didn’t want to use symlinks since some programmes don’t work well with those.
Anyway, could btrfs subvolumes have helped here?

5

Yes. You could create multiple subvolumes and then just mount them as normal.