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Old 03-25-2017, 03:08 PM   #1
Weber Kai
LQ Newbie
 
Registered: Jun 2009
Location: Brasília, Brazil
Distribution: Slackware64
Posts: 29

Rep: Reputation: 22
What's is supposed to be in mtab when using overlay and / readonly?


Hello all!

I am using kvm with slackware64 14.2, with overlay: / is read-only and all data is write in another disk.

Everything works! And I am quite happy. I can clone the empty disk (small qcow2) for each VM and the bigger read-only disk is shared among all VMs!

My setup is: I've added 2 Virtio SCSI disks, each with only 1 partition.
sda1 is the rw one and I have 3 dirs: boot, upper and work.
sdb1 is the ro and I have a fresh new install of Slackware64 14.2 .

After start, lilo loads my custom initrd, then I mount sda1 in /mntrw and sdb1 in /mntro .
I've commented out default /mnt mount command. Instead, I am mounting overlay in /mnt: lowerdir=/mntro,upperdir=/mntrw/upper,workdir=/mntrw/work

I also move the /mntrw and /mntro to /mnt/mnt/mntrw and /mnt/mnt/mntro, so my disks will be accessible after next command.

Finally I do default "exec switch_root /mnt $INIT $RUNLEVEL"

--
This line is commented out in init and instead I execute others below, everything else remains the same:
Quote:
#mount -o ro -t $ROOTFS $ROOTDEV /mnt

mkdir /mntrw
mkdir /mntro

mount -t ext4 /dev/sda1 /mntrw -o rw,discard
mount -t ext4 /dev/sdb1 /mntro -o ro

mount -t overlay -o lowerdir=/mntro,upperdir=/mntrw/upper,workdir=/mntrw/work overlayroot /mnt

mount -o move /mntrw /mnt/mnt/mntrw
mount -o move /mntro /mnt/mnt/mntro
--
But when I execute "mount" to see the mounts... I can't see who is mounted on /, since its a overlay started in /mnt in init filesystem. But the mounts are visible on /proc/mounts.

So my question is... Since / is overlay, what is supposed to be in mtab after all this?
There are some kind of mark to say / is a virtual filesystem, and to mark /dev/sda1 and /dev/sdb1 as already mounted in this system?

Thank you!

Last edited by Weber Kai; 03-25-2017 at 06:35 PM.
 
Old 03-25-2017, 06:58 PM   #2
Weber Kai
LQ Newbie
 
Registered: Jun 2009
Location: Brasília, Brazil
Distribution: Slackware64
Posts: 29

Original Poster
Rep: Reputation: 22
Hi,

Adding those lines to /etc/fstab helped:
Quote:
/dev/sda1 /mnt/mntrw ext4 noauto,rw,discard 0 0
/dev/sdb1 /mnt/mntro ext4 noauto,ro 0 0
overlayroot / overlay noauto,lowerdir=/mntro,upperdir=/mntrw/upper,workdir=/mntrw/work 0 0
Now I can see / is overlay, but I still can see /dev/sda1 and /dev/sdb1 only in /proc/mounts, not in mtab?

Thanks!
 
Old 03-25-2017, 07:03 PM   #3
Weber Kai
LQ Newbie
 
Registered: Jun 2009
Location: Brasília, Brazil
Distribution: Slackware64
Posts: 29

Original Poster
Rep: Reputation: 22
Hi!

These commands (from Jan Rafaj Slackware FB group) solved the problem!

mount /dev/sda1 /mnt/mntrw/ -o rw,discard,remount
mount /dev/sdb1 /mnt/mntro/ -o ro,remount

Thanks!
 
  


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