5.8 Запуск guix time-machine

Команда guix time-machine предоставляет доступ к другим версиям Guix, например, для установки более старых версий пакетов или для воспроизведения вычислений в идентичной среде. Версия используемого Guix определяется коммитом или файлом описания канала, созданным guix describe (see Вызов 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 possibly other channels specified by your channels.scm configuration files—see below) and runs its guix environment command to spawn an environment in a container running guile (guix environment has since been subsumed by guix shell; see Вызов guix shell). It’s like driving a DeLorean¹²! The first guix time-machine 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.

As for guix pull, in the absence of any options, time-machine fetches the latest commits of the channels specified in ~/.config/guix/channels.scm, /etc/guix/channels.scm, or the default channels; the -q option lets you ignore these configuration files. The command:

guix time-machine -q -- build hello

will thus build the package hello as defined in the main branch of Guix, without any additional channel, which is in general a newer revision of Guix than you have installed. Time travel works in both directions!

Примечание: The history of Guix is immutable and guix time-machine provides 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-machine opens the door to security vulnerabilities. See --allow-downgrades.

Due to guix time-machine relying on the “inferiors” mechanism (see Младшие версии), the oldest commit it can travel to is commit ‘6298c3ff’ (“v1.0.0”), dated May 1^st, 2019, which is the first release that included the inferiors mechanism. An error is returned when attempting to navigate to older commits.

Примечание: Although it should technically be possible to travel to such an old commit, the ease to do so will largely depend on the availability of binary substitutes. When traveling to a distant past, some packages may not easily build from source anymore. One such example are old versions of Python 2 which had time bombs in its test suite, in the form of expiring SSL certificates. This particular problem can be worked around by setting the hardware clock to a value in the past before attempting the build.

Основной синтаксис:

guix time-machine options… -- command arg…

где command и arg… передаются без изменений в команду guix указанной ревизии. options, которые определяют эту ревизию, такие же, как и для guix pull (see Вызов guix pull):

--url=url

--commit=commit

--branch=branch

Use the 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.

--channels=file

-C file

Считать список каналов из файла file вместо ~/.config/guix/channels.scm. file должен содержать код Scheme, который определяет список объектов "канал". См. See Каналы для подробной информации.

--no-channel-files

-q

Inhibit loading of the user and system channel files, ~/.config/guix/channels.scm and /etc/guix/channels.scm.

Thus, guix time-machine -q is equivalent to the following Bash command, using the “process substitution” syntax (see Process Substitution in The GNU Bash Reference Manual):

guix time-machine -C <(echo %default-channels) …

Если указанные пакеты ещё не собраны, guix archive автоматически соберёт их. Процесс сборки может контролироваться обычными опциями сборки (see Стандартные параметры сборки).