guix time-machine command provides access to other
revisions of Guix, for example to install older versions of packages,
or to reproduce a computation in an identical environment. The revision
of Guix to be used is defined by a commit or by a channel
description file created by
(see Invoking guix describe).
Let’s assume that you want to travel to those days of November 2020 when
version 1.2.0 of Guix was released and, once you’re there, run the
guile of that time:
guix time-machine --commit=v1.2.0 -- \ environment -C --ad-hoc guile -- guile
The command above fetches Guix 1.2.0 and runs its
environment command to spawn an environment in a container running
guix environment has since been subsumed by
guix shell; see Invoking guix shell). It’s like driving a
DeLorean12! The first
invocation can be expensive: it may have to download or even build a
large number of packages; the result is cached though and subsequent
commands targeting the same commit are almost instantaneous.
Note: The history of Guix is immutable and
guix time-machineprovides the exact same software as they are in a specific Guix revision. Naturally, no security fixes are provided for old versions of Guix or its channels. A careless use of
guix time-machineopens the door to security vulnerabilities. See --allow-downgrades.
The general syntax is:
guix time-machine options… -- command arg…
where command and arg… are passed unmodified to the
guix command of the specified revision. The options that define
this revision are the same as for
guix pull (see Invoking guix pull):
guix channel from the specified url, at the
given commit (a valid Git commit ID represented as a hexadecimal
string or the name of a tag), or branch.
Read the list of channels from file. file must contain Scheme code that evaluates to a list of channel objects. See Channels for more information.
guix pull, the absence of any options means that the
latest commit on the master branch will be used. The command
guix time-machine -- build hello
will thus build the package
hello as defined in the master branch,
which is in general a newer revision of Guix than you have installed.
Time travel works in both directions!
guix time-machine can trigger builds of channels and
their dependencies, and these are controlled by the standard build
options (see Common Build Options).
If you don’t know what a DeLorean is, consider traveling back to the 1980’s.