6.5 Invoking guix gc

Packages that are installed, but not used, may be garbage-collected. The guix gc command allows users to explicitly run the garbage collector to reclaim space from the /gnu/store directory. It is the only way to remove files from /gnu/store—removing files or directories manually may break it beyond repair!

The garbage collector has a set of known roots: any file under /gnu/store reachable from a root is considered live and cannot be deleted; any other file is considered dead and may be deleted. The set of garbage collector roots (“GC roots” for short) includes default user profiles; by default, the symlinks under /var/guix/gcroots represent these GC roots. New GC roots can be added with guix build --root, for example (see Invoking guix build). The guix gc --list-roots command lists them.

Prior to running guix gc --collect-garbage to make space, it is often useful to remove old generations from user profiles; that way, old package builds referenced by those generations can be reclaimed. This is achieved by running guix package --delete-generations (see Invoking guix package).

Our recommendation is to run a garbage collection periodically, or when you are short on disk space. For instance, to guarantee that at least 5 GB are available on your disk, simply run:

guix gc -F 5G

It is perfectly safe to run as a non-interactive periodic job (see Scheduled Job Execution, for how to set up such a job). Running guix gc with no arguments will collect as much garbage as it can, but that is often inconvenient: you may find yourself having to rebuild or re-download software that is “dead” from the GC viewpoint but that is necessary to build other pieces of software—e.g., the compiler tool chain.

The guix gc command has three modes of operation: it can be used to garbage-collect any dead files (the default), to delete specific files (the --delete option), to print garbage-collector information, or for more advanced queries. The garbage collection options are as follows:

--collect-garbage[=min]

-C [min]

Collect garbage—i.e., unreachable /gnu/store files and sub-directories. This is the default operation when no option is specified.

When min is given, stop once min bytes have been collected. min may be a number of bytes, or it may include a unit as a suffix, such as MiB for mebibytes and GB for gigabytes (see size specifications in GNU Coreutils).

When min is omitted, collect all the garbage.

--free-space=free

-F free

Collect garbage until free space is available under /gnu/store, if possible; free denotes storage space, such as 500MiB, as described above.

When free or more is already available in /gnu/store, do nothing and exit immediately.

--delete-generations[=duration]

-d [duration]

Before starting the garbage collection process, delete all the generations older than duration, for all the user profiles and home environment generations; when run as root, this applies to all the profiles of all the users.

For example, this command deletes all the generations of all your profiles that are older than 2 months (except generations that are current), and then proceeds to free space until at least 10 GiB are available:

guix gc -d 2m -F 10G

--delete

-D

Attempt to delete all the store files and directories specified as arguments. This fails if some of the files are not in the store, or if they are still live.

--list-failures

List store items corresponding to cached build failures.

This prints nothing unless the daemon was started with --cache-failures (see --cache-failures).

--list-roots

List the GC roots owned by the user; when run as root, list all the GC roots.

--list-busy

List store items in use by currently running processes. These store items are effectively considered GC roots: they cannot be deleted.

--clear-failures

Remove the specified store items from the failed-build cache.

Again, this option only makes sense when the daemon is started with --cache-failures. Otherwise, it does nothing.

--list-dead

Show the list of dead files and directories still present in the store—i.e., files and directories no longer reachable from any root.

--list-live

Show the list of live store files and directories.

In addition, the references among existing store files can be queried:

--references ¶

--referrers

List the references (respectively, the referrers) of store files given as arguments.

--requisites ¶

-R

List the requisites of the store files passed as arguments. Requisites include the store files themselves, their references, and the references of these, recursively. In other words, the returned list is the transitive closure of the store files.

See Invoking guix size, for a tool to profile the size of the closure of an element. See Invoking guix graph, for a tool to visualize the graph of references.

--derivers ¶

Return the derivation(s) leading to the given store items (see Derivations).

For example, this command:

guix gc --derivers $(guix package -I ^emacs$ | cut -f4)

returns the .drv file(s) leading to the emacs package installed in your profile.

Note that there may be zero matching .drv files, for instance because these files have been garbage-collected. There can also be more than one matching .drv due to fixed-output derivations.

Lastly, the following options allow you to check the integrity of the store and to control disk usage.

--verify[=options] ¶

Verify the integrity of the store.

By default, make sure that all the store items marked as valid in the database of the daemon actually exist in /gnu/store.

When provided, options must be a comma-separated list containing one or more of contents and repair.

When passing --verify=contents, the daemon computes the content hash of each store item and compares it against its hash in the database. Hash mismatches are reported as data corruptions. Because it traverses all the files in the store, this command can take a long time, especially on systems with a slow disk drive.

Using --verify=repair or --verify=contents,repair causes the daemon to try to repair corrupt store items by fetching substitutes for them (see Substitutes). Because repairing is not atomic, and thus potentially dangerous, it is available only to the system administrator. A lightweight alternative, when you know exactly which items in the store are corrupt, is guix build --repair (see Invoking guix build).

--optimize ¶

Optimize the store by hard-linking identical files—this is deduplication.

The daemon performs deduplication after each successful build or archive import, unless it was started with --disable-deduplication (see --disable-deduplication). Thus, this option is primarily useful when the daemon was running with --disable-deduplication.

--vacuum-database ¶

Guix uses an sqlite database to keep track of the items in (see The Store). Over time it is possible that the database may grow to a large size and become fragmented. As a result, one may wish to clear the freed space and join the partially used pages in the database left behind from removed packages or after running the garbage collector. Running sudo guix gc --vacuum-database will lock the database and VACUUM the store, defragmenting the database and purging freed pages, unlocking the database when it finishes.