This is required on systemd, which mounts filesystems as "shared"
subtrees. Changes to shared trees in a private mount namespace are
propagated to the outside world, which is bad.
Setting the environment variable NIX_COUNT_CALLS to 1 enables some
basic profiling in the evaluator. It will count calls to functions
and primops as well as evaluations of attributes.
For example, to see where evaluation of a NixOS configuration spends
its time:
$ NIX_SHOW_STATS=1 NIX_COUNT_CALLS=1 ./src/nix-instantiate/nix-instantiate '<nixos>' -A system --readonly-mode
...
calls to 39 primops:
239532 head
233962 tail
191252 hasAttr
...
calls to 1595 functions:
224157 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/lists.nix:17:19'
221767 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/lists.nix:17:14'
221767 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/lists.nix:17:10'
...
evaluations of 7088 attributes:
167377 undefined position
132459 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/attrsets.nix:119:41'
47322 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/attrsets.nix:13:21'
...
In a private PID namespace, processes have PIDs that are separate from
the rest of the system. The initial child gets PID 1. Processes in
the chroot cannot see processes outside of the chroot. This improves
isolation between builds. However, processes on the outside can see
processes in the chroot and send signals to them (if they have
appropriate rights).
Since the builder gets PID 1, it serves as the reaper for zombies in
the chroot. This might turn out to be a problem. In that case we'll
need to have a small PID 1 process that sits in a loop calling wait().
Nix now requires SQLite and bzip2 to be pre-installed. SQLite is
detected using pkg-config. We required DBD::SQLite anyway, so
depending on SQLite is not a big problem.
The --with-bzip2, --with-openssl and --with-sqlite flags are gone.
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.
unreachable paths. This matters when using --max-freed etc.:
unreachable paths could become reachable again, so it's nicer to
keep them if there is "real" garbage to be deleted. Also, don't use
readDirectory() but read the Nix store and delete invalid paths in
parallel. This reduces GC latency on very large Nix stores.
* Buffer the HashSink. This speeds up hashing a bit because it
prevents lots of calls to the hash update functions (e.g. nix-hash
went from 9.3s to 8.7s of user time on the closure of my
/var/run/current-system).
significantly cuts down the number of syscalls (e.g., for "nix-store
-qR /var/run/current-system" via the daemon, it reduced the number
of syscalls in the client from 29134 to 4766 and in the daemon from
44266 to 20666).
because it defines _FILE_OFFSET_BITS. Without this, on
OpenSolaris the system headers define it to be 32, and then
the 32-bit stat() ends up being called with a 64-bit "struct
stat", or vice versa.
This also ensures that we get 64-bit file sizes everywhere.
* Remove the redundant call to stat() in parseExprFromFile().
The file cannot be a symlink because that's the exit condition
of the loop before.
exception handler, otherwise throw an exception. We need to ignore
write errors in exception handlers to ensure that cleanup code runs
to completion if the other side of stderr has been closed
unexpectedly.
hook script proper, and the stdout/stderr of the builder. Only the
latter should be saved in /nix/var/log/nix/drvs.
* Allow the verbosity to be set through an option.
* Added a flag --quiet to lower the verbosity level.
it requires a certain feature on the build machine, e.g.
requiredSystemFeatures = [ "kvm" ];
We need this in Hydra to make sure that builds that require KVM
support are forwarded to machines that have KVM support. Probably
this should also be enforced for local builds.
changed. This prevents corrupt paths from spreading to other
machines. Note that checking the hash is cheap because we're
hashing anyway (because of the --sign feature).
