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I just came up with an unusual issue with Ubuntu 18 installation and the 1st boot. If I have two disks, one mounted at / and the other mounted at /opt, the installation succeeds and boots without any issue.

But if I use one disk for / and the other disk for /etc, even though installation succeeds, the system won't start up. It will be in a loop.

Anyone came across this issue?

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There's no good reason to ever mount /etc on either a separate slice, or disk. In fact it's a really bad idea (as you have just discovered).

The reason being; /etc holds all the (system) startup (init, fstab), and configuration data that determines what hardware to address, and what services to start. How to address that hardware, and how to start the services. If you mount /etc on a separate disk, or slice, the system can't see it (yet) because it doesn't have access to (all) the information it needs to know that it needs to know to even mount it -- whew, that was a mouthful.

Hope this makes sense. But in other words; don't mount /etc on a separate disk -- ever. :)

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  • If I'm correct it could do on previous versions. Thanks for the explanation.
    – Thameera
    Jun 27 '19 at 7:43
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Are you trying to mount /etc via /etc/fstab available only on the other disk? Can you see the flaw now?

I guess you need /etc on the root disk, so (separate!) fstab can be read and eventually mount the desired /etc from the other disk. Other files in the initial /etc may be in use before the desired one is mounted, so you would need to maintain (a stub) /etc on your root filesystem anyway. This could be a mess.

With systemd you can mount without fstab, yet the configuration still lives within /etc.

There may be workarounds. This question on Unix & Linux SE is somewhat useful: Moving /etc to separate partition.

Anyway I would keep things simple and not mount /etc separately. Normally it stores so little amount of data it should fit in the root filesystem. If there is not enough room in / for /etc then you shouldn't use Ubuntu (which is not a tiny distro) in the first place.

Mounting /etc separately only adds problems, solves nothing. Drop the idea.

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  • I didn't mount the /etc after install. I did it when setup disk in installation. And Ubuntu didn't prohibit or show warning about this. I think it should show some warning or error when select separate disk for /etc. Thanks for the explanation.
    – Thameera
    Jun 27 '19 at 7:45

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