sharing package directories (i.e., the result of building a Nix
descriptor).
`nix-pull-prebuilts' obtains a list of all known prebuilts by
consulting the paths and URLs specified in
$prefix/etc/nix/prebuilts.conf. The mappings ($pkghash,
$prebuilthash) and ($prebuilthash, $location) are registered with
Nix so that it can use the prebuilt with hash $prebuilthash when
installing a package with hash $pkghash by downloading and unpacking
$location.
`nix-push-prebuilts' creates prebuilts for all packages for which no
prebuilt is known to exist. It can then optionally upload these
to the network through rsync.
`nix-[pull|push]-prebuilts' just provide a policy. Nix provides the
mechanism through the `nix [export|regprebuilt|regurl]' commands.
doesn't actually delete any packages, it just prints their
descriptor hashes. So we can do
nix info $(nix-collect-garbage)
to print out the ids of the packages that would be deleted, and
nix delpkg $(nix-collect-garbage)
to actually delete them.
This allows us to find out all `live' packages on the system by
doing
nix closure $(cat /nix/var/nix/links/*.hash)
which will print out the activated configurations and all packages
referenced by them. We could then garbage collect unused packages
by deleting the difference between `nix listinst' and the set
returned by `nix closure ...'.
build action for `system' packages (like system.fix) that have
dependencies on all packages we want to activate.
So the command sequence to switch to a new activation configuration
of the system would be:
$ fix -i .../fixdescriptors/system.fix
...
system.fix -> 89cf4713b37cc66989304abeb9ea189f
$ nix-switch 89cf4713b37cc66989304abeb9ea189f
* A nix-profile.sh script that can be included in .bashrc.
