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I want several Linux distros to share the same home/data partition, each having a unique user name and implicitly a separate home directory. I installed Debian Wheezy, and formatted this partition as btrfs. But then, when I install Ubuntu 13.04 and select that partition as /home it creates a new directory, @home, in which it puts another folder with the user name.

Why does this happen?

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13.04 or 12.04? –  don.joey Jan 5 '13 at 13:08

2 Answers 2

up vote 2 down vote accepted

I'm guessing Ubuntu always wants to use subvolumes, if you use btrfs for the root partition you will automatically get two subvolumes, "@/" and "@home/" (see the Ubuntu wiki btrfs entry for more info on this), and it might set up the "@home/" subvolume just for the sake of consistency.

On a side note: If you look in /etc/fstab you should see the option "subvol=@home" for the /home mountpoint, which means that it mounts the "@home/" subvolume of that btrfs (subvolumes are quite similar to directories in some sense).


Answer to comment:

Yes, you can mount the top node and the subvolume node simultaneously:

mount /dev/sdX# /mnt/top_node -o subvolid=5
mount /dev/sdX# /mnt/home_subvol -o subvol=@home

(If the top node is the default mount point (default case) you can omit the "-o subvolid=5" option)

Here the @home/ subvolume will be accessible both through /mnt/top_node/@home/ and /mnt/home_subvol/ equivalently.

It might be worth it to have the two dirs there alongside @home/ be subvolumes instead, that way you could snapshot and mount them all independently...

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But I would like to access directories above "@home" from Ubuntu. Now, on that partition I have: data_dir, wheezy_home_dir and "@home", in which there is ubuntu_home_dir. The trick is, I cannot access data_dir or anything above "@home". Can I do that? –  Miggs Jan 5 '13 at 11:31
    
Yes, see edits above, by the way, why is the ubuntu_home_dir folder there, shouldn't it suffice with just @home/username if it's mounted correctly (i.e. the @home/ subvolume node is mounted at /home)? –  arand Jan 5 '13 at 12:40

I really hope this helps others who went down my path. I installed my root partition to btrfs. After booting it appeared to hang after scanning for btrfs partitions ....something about system v compatability. Someone in another thread said do a "soft shutdown" which worked for a second. Then I tried to turn on compression in the /etc/fstab file with compress=lzo. Unfortunately I put a space between theses settings here:

---->defaults, compress=lzo<-----

this leads to booting the system but not having a home directory when ctrl-alt-f4 and logging in. For example, It will say no directory and set your home directory to HOME=/ and you will see the root directory listing for your home.

if you did this remove the space so it reads defaults,compress=lzo

it kept an idiot like me occupied for days.

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