Guix can look up and fetch substitutes from several servers. This is useful when you are using packages from additional channels for which the official server does not have substitutes but another server provides them. Another situation where this is useful is when you would prefer to download from your organization’s substitute server, resorting to the official server only as a fallback or dismissing it altogether.
You can give Guix a list of substitute server URLs and it will check them in the specified order. You also need to explicitly authorize the public keys of substitute servers to instruct Guix to accept the substitutes they sign.
On Guix System, this is achieved by modifying the configuration of the
guix service. Since the
guix service is part of the
default lists of services,
%desktop-services, you can use
modify-services to change
its configuration and add the URLs and substitute keys that you want
As an example, suppose you want to fetch substitutes from
guix.example.org and to authorize the signing key of that server,
in addition to the default
resulting operating system configuration will look something like:
(operating-system ;; … (services ;; Assume we're starting from '%desktop-services'. Replace it ;; with the list of services you're actually using. (modify-services %desktop-services (guix-service-type config => (guix-configuration (inherit config) (substitute-urls (append (list "https://guix.example.org") %default-substitute-urls)) (authorized-keys (append (list (local-file "./key.pub")) %default-authorized-guix-keys)))))))
This assumes that the file key.pub contains the signing key of
guix.example.org. With this change in place in your operating
system configuration file (say /etc/config.scm), you can
reconfigure and restart the
guix-daemon service or reboot so the
changes take effect:
$ sudo guix system reconfigure /etc/config.scm $ sudo herd restart guix-daemon
If you’re running Guix on a “foreign distro”, you would instead take the following steps to get substitutes from additional servers:
guix-daemon; when using systemd, this is normally /etc/systemd/system/guix-daemon.service. Add the --substitute-urls option on the
guix-daemoncommand line and list the URLs of interest (see
… --substitute-urls='https://guix.example.org https://ci.guix.gnu.org'
systemctl daemon-reload systemctl restart guix-daemon.service
guix archive --authorize < key.pub
Again this assumes key.pub contains the public key that
guix.example.org uses to sign substitutes.
Now you’re all set! Substitutes will be preferably taken from
as a fallback. Of course you can list as many substitute servers as you
like, with the caveat that substitute lookup can be slowed down if too
many servers need to be contacted.
Note that there are also situations where one may want to add the URL of a substitute server without authorizing its key. See Substitute Authentication, to understand this fine point.