With this flag, if any valid derivation output is missing or corrupt,
it will be recreated by using a substitute if available, or by
rebuilding the derivation. The latter may use hash rewriting if
chroots are not available.
This operation allows fixing corrupted or accidentally deleted store
paths by redownloading them using substituters, if available.
Since the corrupted path cannot be replaced atomically, there is a
very small time window (one system call) during which neither the old
(corrupted) nor the new (repaired) contents are available. So
repairing should be used with some care on critical packages like
Glibc.
In Nixpkgs, the attribute in all-packages.nix corresponding to a
package is usually equal to the package name. However, this doesn't
work if the package contains a dash, which is fairly common. The
convention is to replace the dash with an underscore (e.g. "dbus-lib"
becomes "dbus_glib"), but that's annoying. So now dashes are valid in
variable / attribute names, allowing you to write:
dbus-glib = callPackage ../development/libraries/dbus-glib { };
and
buildInputs = [ dbus-glib ];
Since we don't have a negation or subtraction operation in Nix, this
is unambiguous.
Using the immutable bit is problematic, especially in conjunction with
store optimisation. For instance, if the garbage collector deletes a
file, it has to clear its immutable bit, but if the file has
additional hard links, we can't set the bit afterwards because we
don't know the remaining paths.
So now that we support having the entire Nix store as a read-only
mount, we may as well drop the immutable bit. Unfortunately, we have
to keep the code to clear the immutable bit for backwards
compatibility.
It turns out that the immutable bit doesn't work all that well. A
better way is to make the entire Nix store a read-only bind mount,
i.e. by doing
$ mount --bind /nix/store /nix/store
$ mount -o remount,ro,bind /nix/store
(This would typically done in an early boot script, before anything
from /nix/store is used.)
Since Nix needs to be able to write to the Nix store, it now detects
if /nix/store is a read-only bind mount and then makes it writable in
a private mount namespace.
Commit 6a214f3e06 copied most of the Nix
shell initialisation code from NixOS to nix-profile.sh; however, that
code assumes a multi-user install and is Linux-specific (e.g. it calls
the "stat" command). So go back to the simple single-user version.
Fixes#49.
Negative lookups are purged from the DB after a day, at most once per
day. However, for non-"have" lookups (e.g. all except "nix-env
-qas"), negative lookups are ignored after one hour. This is to
ensure that you don't have to wait a day for an operation like
"nix-env -i" to start using new binaries in the cache.
Should probably make this configurable.
The outputs of a derivation can refer to each other (even though they
cannot have cycles), so they have to be deleted in the right order.
http://hydra.nixos.org/build/3026118
If the options gc-keep-outputs and gc-keep-derivations are both
enabled, you can get a cycle in the liveness graph. There was a hack
to handle this, but it didn't work with multiple-output derivations,
causing the garbage collector to fail with errors like ‘error: cannot
delete path `...' because it is in use by `...'’. The garbage
collector now handles strongly connected components in the liveness
graph as a unit and decides whether to delete all or none of the paths
in an SCC.
Note that this will only work if the client has a very recent Nix
version (post 15e1b2c223), otherwise the
--option flag will just be ignored.
Fixes#50.
Apparently our DBD::SQLite links against /usr/lib/libsqlite3.dylib,
which is an old version that doesn't respect foreign key constraints.
So manifests/cache.sqlite doesn't get updated properly when a manifest
disappears. We should fix our DBD::SQLite, but in the meantime this
will fix the test.
http://hydra.nixos.org/build/3017959
