are both front-ends to official build farms that build packages from Guix
continuously for some architectures, and make them available as
substitutes. These are the default source of substitutes; which can be
overridden by passing the --substitute-urls option either to
--substitute-urls) or to client tools such as
(see client --substitute-urls option).
Substitute URLs can be either HTTP or HTTPS. HTTPS is recommended because communications are encrypted; conversely, using HTTP makes all communications visible to an eavesdropper, who could use the information gathered to determine, for instance, whether your system has unpatched security vulnerabilities.
Substitutes from the official build farms are enabled by default when using Guix System (see GNU发行版). However, they are disabled by default when using Guix on a foreign distribution, unless you have explicitly enabled them via one of the recommended installation steps (see 安装). The following paragraphs describe how to enable or disable substitutes for the official build farm; the same procedure can also be used to enable substitutes for any other substitute server.