Re: Systemd bybasses fstab mounting root partition(?)

["Karl E. Jorgensen" <karl@jorgensen.org.uk>]

Hi

On Mon, 2015-10-19 at 18:24 +0300, Ivan Boro wrote:
> Looks like subj.
> Have a KVM machine with jessie assembled via debootstrap. Fstab states
> 
> /dev/vda2       /       ext4    rw      0       0
> 
> The partition labeled vda2 is listed in grub.cfg as the root partition
> by its uuid.(via update-grub)
> 
> Added a disk to have swap on it. Booted normally, despite the fact, that
> the new swap-disk was automatically labeled as vda and the disk with
> root is as vdb:
> 
> # mount | grep ' / '
> /dev/vdb2 on / type ext4 (rw,relatime,data=ordered)
> 
> No errors or warnings in dmesg.
> 
> So, systemd mounted root partition, whitout looking into fstab.
> 
> I don't have much experience in systemd, and now wonder how this "smart"
> mount works.

Well - I doubt this is systemd specific.

/etc/fstab is in the root file system.  Thus, the system can only
examine /etc/fstab _after_ the root file system has been mounted...

Instead you may want to examine the kernel command line (e.g. in grub
or /proc/cmdline) - it should have "root=xxxx" in it. Nowadays that is
often specified via a UUID - and the UUID stays the same if if you move
disks about.

Hope this helps
-- 
Karl E. Jorgensen