Wednesday, May 18, 2016

Installing Tribblix into an existing pool

The normal installation method for Tribblix is the script.

This creates a ZFS pool for installation into, creates file systems, copies the OS, adds packages, makes a few customizations, installs the bootloader, and not much else. It's designed to be simple.

(There's an alternative, to install to a UFS file system. Not much used, but it's kept just to ensure no insidiuous dependencies creep into the regular installer, and is useful for people with older underpowered systems.)

However, if you've already got an illumos distro installed, then you might already have a ZFS pool, and it might also have some useful data you would rather not wipe everything out. Is there not a way to create a brand new boot environment in the existing pool and install Tribblix to that, preserving all your data?

(Remember, also, that  ZFS encourages the separation of OS and data. So you should be able to replace the OS without disturbing the data.)

As of Tribblix Milestone 17, this will work. Booting from the ISO and logging in, you'll find a script called in root's home directory. You can use that instead of, like so:

./ -B rpool kitchen-sink

You have to give it the name of the existing bootable pool, usually rpool. It will do a couple of sanity checks to be sure this pool is suitable, but will then create a new BE there and install to that.

Arguments after the pool name are overlays, specifying what software to install, just like the regular install.

It will update grub for you, so that you have a grub on the pool that is compatible with the version of illumos you've just added. With -B, it will update the MBR as well.

It copies some files, the minimum that define the system's identity, from the existing bootable system into the new BE. This basically copies across user accounts (group, passwd, shadow files) and the system's ssh keys, but nothing else.

Any existing zfs file systems are untouched, and will be present in the new system. You'll have to import any additional zfs pools, though.

When you boot up after this, the grub menu will just contain the new BE you just created. However, any old boot environments are still present, so you can still see them, and manipulate them, using beadm. In particular, you can mount up and old BE (in case there are important files you need to get back), and activate an old BE so you can boot into the old system if so desired.

Amongst other things, you can use this as a recovery tool, when your existing system has a functioning root pool but won't boot.

I've also used this to "upgrade" older Tribblix systems. While there is an upgrade mechanism, this really only works (a) for very recent releases, and (b) to update one release at a time. With this new mechanism, I can simply stick a new copy of Milestone 17 on an old box, and enjoy the new version while having all my data intact.

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