pzakha's questions

I'm trying to figure out how to configure my DHCP client on Ubuntu server 18.04.

I have the following netplan configuration, coming from cloud-init:

network:
    version: 2
    ethernets:
        ens160:
            dhcp4: true
            match:
                macaddress: 02:dc:01:00:38:4c
            set-name: ens160

This seems to properly configure my network interface with an ip address, dns, default gateway and search domain. However, I'm wondering how to obtain a hostname from DHCP. I've been looking into dhclient which provides some convenient hooks that I can use, however it doesn't appear that dhclient hooks are being called. I've noticed that cloud-init calls dhclient as per the logs, but as some sort of sandboxed version, which seems to ignore the hooks.

I've also noticed that systemd-networkd reports some DHCP activity regarding to DHCP leases.

Could someone shed some light into the process?

I'm trying to design a framework that would allow me to do full transactional upgrade of Ubuntu and the root file system.

The requirement is that if my upgrade fails I want to be able to roll back to the exact state I was at before.

Ubuntu Core seems to be providing the exact kind of functionality I need, but it comes with a lot of security limitations, and is really a fairly different system compared to classical Ubuntu.

One option is to have 2 partitions. I'd install the new version of the OS on the 2nd partition, re-apply all my configurations and then update grub to boot from that partition.

However, I'd then need to decide on the size of each partition which is not ideal. This would also make it more complicated to share some directories between the 2 versions of the OS (i.e., instead of copying logs in /var, I'd rather be able to just bind-mount /var from somewhere else).

What I'm thinking is having a root directory with a bunch of empty directories /etc, /lib, /opt, etc., and one directory such as /versions which would contain my different versions of the OS. E.g. /versions/v1/, /versions/v2/.

At boot time, the boot process would select the right version and then bind mount each of the child directories onto the root subdirectories.

In other words, if I want to boot from /versions/v2, it would bind mount: /versions/v2/etc on /etc /versions/v2/opt on /opt etc.

What I'm wondering is if this is the right approach to this problem and if so then how could that be accomplished.