Xubuntu 16.04: fstab won't mount "/root" entry

Question

A week ago, I installed Xubuntu 16.04 and supposed to mount a partition(/dev/sda3) for root's home (/root). Here is my fstab looks like:

# / was on /dev/sda5 during installation
UUID=81f2f987-b411-4579-a3e5-8e92f66567ac /               ext4    errors=remount-ro 0       1
# /root was on /dev/sda3 during installation
UUID=bbf21f07-54ec-4515-a31b-7767fbfe985d /root           ext4    defaults        0       2
# swap was on /dev/sda6 during installation
UUID=717a9bb5-cb8f-48f7-bd4f-56bfafe431be none            swap    sw              0       0

and fdisk -l:

Device     Boot     Start       End   Sectors  Size Id Type
/dev/sda1  *         2048    206847    204800  100M  7 HPFS/NTFS/exFAT
/dev/sda2          206848 204799999 204593152 97.6G  7 HPFS/NTFS/exFAT
/dev/sda3       204800000 307199999 102400000 48.8G 83 Linux
/dev/sda4       307200000 468860927 161660928 77.1G  5 Extended
/dev/sda5       307202048 368642047  61440000 29.3G 83 Linux
/dev/sda6       368644096 370741247   2097152    1G 82 Linux swap / Solaris
/dev/sda7       370743296 468860927  98117632 46.8G 83 Linux

blkid /dev/sda3:

/dev/sda3: LABEL="home" UUID="bbf21f07-54ec-4515-a31b-7767fbfe985d" TYPE="ext4" PARTUUID="e25cf333-03"

At first, /dev/sda3 sometimes mounted to /root, sometimes not. After I reboot several times, it doesn't mount at all. As well as specify device's file name:

/dev/sda3  /root           ext4    defaults        0       2

I tried mount to /test by UUID form, it works. On Debian Jessie and Xubuntu 14.04, this problem doesn't exist at all.

At last, I use label to denote device:

LABEL=home  /root           ext4    defaults        0       2

Successfully mounted, at least until I'm asking this question here. But I have no clue why /dev/sda3 is not mounted to root in previous cases. Does Ubuntu disable this for security reasons?

Answer 1

As a general rule, it's inadvisable (at best) to make /root a separate partition from the root (/) filesystem. The reason is that this is the root user's home directory, and it's critical that this location remain accessible even in the event of a severe problem, such as damage to the /etc/fstab file.

I don't know if that's related to your problem, but it might be -- it's conceivable that there's something in the Ubuntu startup or shutdown procedure that's interacting badly with use of a separate /root partition. Certainly use of a separate /root partition is so rare that this case would get absolutely no testing by Ubuntu's developers.

I recommend you reconsider this practice. Given Ubuntu's security model, /root probably contains few or no files, aside from boilerplate account files. If you're storing anything there (especially anything big enough to warrant creating a separate partition for those files), it could be another location would be more sensible.