Chroots are initialised by hard-linking inputs from the Nix store to
the chroot. This doesn't work if the input has its immutable bit set,
because it's forbidden to create hard links to immutable files. So
temporarily clear the immutable bit when creating and destroying the
chroot.
Note that making regular files in the Nix store immutable isn't very
reliable, since the bit can easily become cleared: for instance, if we
run the garbage collector after running ‘nix-store --optimise’. So
maybe we should only make directories immutable.
I was bitten one time too many by Python modifying the Nix store by
creating *.pyc files when run as root. On Linux, we can prevent this
by setting the immutable bit on files and directories (as in ‘chattr
+i’). This isn't supported by all filesystems, so it's not an error
if setting the bit fails. The immutable bit is cleared by the garbage
collector before deleting a path. The only tricky aspect is in
optimiseStore(), since it's forbidden to create hard links to an
immutable file. Thus optimiseStore() temporarily clears the immutable
bit before creating the link.
directory. Previously in this situation we did add the Nix
expressions from the channel to allow installation from source, but
this doesn't work for binary-only channels and leads to confusing
error messages.
Without these, Nix fails on 32-bit Linux with Perl 5.14, with a
rather unhelpful error message:
Not a CODE reference at /nix/store/n6kpbacn6nn7i3i735v8j3di8aqyl07v-perl-5.14.2/lib/perl5/5.14.2/i686-linux-thread-multi/DynaLoader.pm
This is likely because the lack of -D_FILE_OFFSET_BITS=64 causes
various Perl structures to not match what the Perl interpreter
expects.
environment of the given derivation in a format that can be sourced
by the shell, e.g.
$ eval "$(nix-store --print-env $(nix-instantiate /etc/nixos/nixpkgs -A pkg))"
$ NIX_BUILD_TOP=/tmp
$ source $stdenv/setup
This is especially useful to reproduce the environment used to build
a package outside of its builder for development purposes.
TODO: add a nix-build option to do the above and fetch the
dependencies of the derivation as well.
scripts.
* Include the version and architecture in the -I flag so that there is
at least a chance that a Nix binary built for one Perl version will
run on another version.
^/nix/branches/multiple-outputs-sandbox). Multiple output support
still isn't complete, but it wasn't complete in the trunk either, so
it doesn't hurt.
‘drvAttrs’. This will simplify the implementation of functions such
as ‘overrideDerivation’ in Nixpkgs, which need to filter out any
added attributes such as outPath.
common attribution so that they're evaluated only once, etc. Note
that the default output is now the first element of the "outputs"
attribute, rather than the first element of the sorted list of
outputs. This seems more user-friendly.
other simplifications.
* Use <nix/...> to locate the corepkgs. This allows them to be
overriden through $NIX_PATH.
* Use bash's pipefail option in the NAR builder so that we don't need
to create a temporary file.
