How to roll back a "guix system reconfigure"?

[Chris Marusich <cmmarusich@gmail.com>]

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Hi,

After running a "guix system reconfigure", it is possible to boot to a
previous version of the system by manually selecting it from the GRUB
menu.  However, if you want to permanently roll back to a previous
version (e.g., because something broke), it's a nuisance to do this
every time you boot.  Of course, assuming guix is still working after
the reconfigure, you could simply do another "guix system reconfigure"
using the previous version of your operating system configuration file,
but it seems like that shouldn't be necessary.

What is the recommended way to roll back after a "guix system
reconfigure"?  Is it sufficient to manually edit the grub.cfg file to
remove all mention of the generations after the one to which you want to
roll back?  If you do that, will the gc root(s) associated with the bad
configuration stay around forever?  Would it make sense to add a command
like "guix system roll-back" or "guix system switch-generation", similar
to "guix package --roll-back" and "guix package --switch-generation"?

I ask mainly because I'm just not sure what the "best practice" is
surrounding system-level rollback at this time, and I'd love to know
more.

-- 
Chris

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