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Diffstat (limited to 'doc/guix.texi')
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diff --git a/doc/guix.texi b/doc/guix.texi index d3ab9676ee..fbf5bac9b4 100644 --- a/doc/guix.texi +++ b/doc/guix.texi @@ -2569,6 +2569,10 @@ candidates: guix build guile --with-source=../guile-2.0.9.219-e1bb7.tar.xz @end example +@item --no-grafts +Do not ``graft'' packages. In practice, this means that package updates +available as grafts are not applied. @xref{Security Updates}, for more +information on grafts. @item --derivations @itemx -d @@ -3003,6 +3007,7 @@ For information on porting to other architectures or kernels, * System Installation:: Installing the whole operating system. * System Configuration:: Configuring a GNU system. * Installing Debugging Files:: Feeding the debugger. +* Security Updates:: Deploying security fixes quickly. * Package Modules:: Packages from the programmer's viewpoint. * Packaging Guidelines:: Growing the distribution. * Bootstrapping:: GNU/Linux built from scratch. @@ -4280,6 +4285,64 @@ the load. To check whether a package has a @code{debug} output, use @command{guix package --list-available} (@pxref{Invoking guix package}). +@node Security Updates +@section Security Updates + +@indentedblock +Note: As of version @value{VERSION}, the feature described in this +section is experimental. +@end indentedblock + +@cindex security updates +Occasionally, important security vulnerabilities are discovered in core +software packages and must be patched. Guix follows a functional +package management discipline (@pxref{Introduction}), which implies +that, when a package is changed, @emph{every package that depends on it} +must be rebuilt. This can significantly slow down the deployment of +fixes in core packages such as libc or Bash, since basically the whole +distribution would need to be rebuilt. Using pre-built binaries helps +(@pxref{Substitutes}), but deployment may still take more time than +desired. + +@cindex grafts +To address that, Guix implements @dfn{grafts}, a mechanism that allows +for fast deployment of critical updates without the costs associated +with a whole-distribution rebuild. The idea is to rebuild only the +package that needs to be patched, and then to ``graft'' it onto packages +explicitly installed by the user and that were previously referring to +the original package. The cost of grafting is typically very low, and +order of magnitudes lower than a full rebuild of the dependency chain. + +@cindex replacements of packages, for grafts +For instance, suppose a security update needs to be applied to Bash. +Guix developers will provide a package definition for the ``fixed'' +Bash, say @var{bash-fixed}, in the usual way (@pxref{Defining +Packages}). Then, the original package definition is augmented with a +@code{replacement} field pointing to the package containing the bug fix: + +@example +(define bash + (package + (name "bash") + ;; @dots{} + (replacement bash-fixed))) +@end example + +From there on, any package depending directly or indirectly on Bash that +is installed will automatically be ``rewritten'' to refer to +@var{bash-fixed} instead of @var{bash}. This grafting process takes +time proportional to the size of the package, but expect less than a +minute for an ``average'' package on a recent machine. + +Currently, the graft and the package it replaces (@var{bash-fixed} and +@var{bash} in the example above) must have the exact same @code{name} +and @code{version} fields. This restriction mostly comes from the fact +that grafting works by patching files, including binary files, directly. +Other restrictions may apply: for instance, when adding a graft to a +package providing a shared library, the original shared library and its +replacement must have the same @code{SONAME} and be binary-compatible. + + @node Package Modules @section Package Modules |