The current usage technically works by putting multiple different
repos in to the same git directory. However, it is very slow as
Git tries very hard to find common commits between the two
repositories. If the two repositories are large (like Nixpkgs and
another long-running project,) it is maddeningly slow.
This change busts the cache for existing deployments, but users
will be promptly repaid in per-repository performance.
TransferManager allocates a lot of memory (50 MiB by default), and it
might leak but I'm not sure about that. In any case it was causing
OOMs in hydra-queue-runner. So allocate only one TransferManager per
S3BinaryCacheStore.
Hopefully fixes https://github.com/NixOS/hydra/issues/586.
This callback is executed on a different thread, so exceptions thrown
from the callback are not caught:
Aug 08 16:25:48 chef hydra-queue-runner[11967]: terminate called after throwing an instance of 'nix::Error'
Aug 08 16:25:48 chef hydra-queue-runner[11967]: what(): AWS error: failed to upload 's3://nix-cache/19dbddlfb0vp68g68y19p9fswrgl0bg7.ls'
Therefore, just check the transfer status after it completes. Also
include the S3 error message in the exception.
This didn't work anymore since decompression was only done in the
non-coroutine case.
Decompressors are now sinks, just like compressors.
Also fixed a bug in bzip2 API handling (we have to handle BZ_RUN_OK
rather than BZ_OK), which we didn't notice because there was a missing
'throw':
if (ret != BZ_OK)
CompressionError("error while compressing bzip2 file");
It adds a new operation, cmdAddToStoreNar, that does the same thing as
the corresponding nix-daemon operation, i.e. call addToStore(). This
replaces cmdImportPaths, which has the major issue that it sends the
NAR first and the store path second, thus requiring us to store the
incoming NAR either in memory or on disk until we decide what to do
with it.
For example, this reduces the memory usage of
$ nix copy --to 'ssh://localhost?remote-store=/tmp/nix' /nix/store/95cwv4q54dc6giaqv6q6p4r02ia2km35-blender-2.79
from 267 MiB to 12 MiB.
Probably fixes#1988.
In EvalState::checkSourcePath, the path is checked against the list of
allowed paths first and later it's checked again *after* resolving
symlinks.
The resolving of the symlinks is done via canonPath, which also strips
out "../" and "./". However after the canonicalisation the error message
pointing out that the path is not allowed prints the symlink target in
the error message.
Even if we'd suppress the message, symlink targets could still be leaked
if the symlink target doesn't exist (in this case the error is thrown in
canonPath).
So instead, we now do canonPath() without symlink resolving first before
even checking against the list of allowed paths and then later do the
symlink resolving and checking the allowed paths again.
The first call to canonPath() should get rid of all the "../" and "./",
so in theory the only way to leak a symlink if the attacker is able to
put a symlink in one of the paths allowed by restricted evaluation mode.
For the latter I don't think this is part of the threat model, because
if the attacker can write to that path, the attack vector is even
larger.
Signed-off-by: aszlig <aszlig@nix.build>
This particular `shell` variable wasn't used, since a new one was
declared in the only side of the `if` branch that used a `shell`
variable.
It could realistically confuse developers thinking it could use `$SHELL`
under some situations.
forceValue() were called after a value is copied effectively forcing only one of the copies keeping another copy not evaluated.
This resulted in its evaluation of the same lazy value more than once (the number of hits is not big though)
Not ready for this yet, causes the prompt to disappear in nix repl
and more generally can overwrite non-progress-bar messages.
This reverts commit 44de71a396.
Before:
$ command time nix-prefetch-url https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.17.6.tar.xz
1.19user 1.02system 0:41.96elapsed 5%CPU (0avgtext+0avgdata 182720maxresident)k
After:
1.38user 1.05system 0:39.73elapsed 6%CPU (0avgtext+0avgdata 16204maxresident)k
Note however that addToStore() can still take a lot of memory
(e.g. RemoteStore::addToStore() is constant space, but
LocalStore::addToStore() isn't; that's fixed by
c94b4fc7ee
though).
Fixes#1400.
For example, this allows you to do run nix-daemon as a non-privileged
user:
eelco$ NIX_STATE_DIR=~/my-nix/nix/var nix-daemon --store ~/my-nix/
The NIX_STATE_DIR is still needed because settings.nixDaemonSocketFile
is not derived from settings.storeUri (and we can't derive it from the
store's state directory because we don't want to open the store in the
parent process).
As proposed in #1634 the `nix search` command could use some
improvements. Initially 0413aeb35d added
some basic sorting behavior using `std::map`, a next step would be an
improvement of the output.
This patch includes the following changes:
* Use `$PAGER` for outputs with `RunPager` from `shared.hh`:
The same behavior is defined for `nix-env --query`, furthermore it
makes searching huge results way easier.
* Simplified result blocks:
The new output is heavily inspired by the output from `nox`, the first
line shows the attribute path and the derivaiton name
(`attribute path (derivation name)`) and the description in the second
line.
Slightly nicer behavior when updates are somewhat far apart
(during a long linking step, perhaps) ensuring things
don't appear unresponsive.
If we wait the maximum amount for the update,
don't bother waiting another 50ms (for rate-limiting purposes)
and just check if we should quit.
This also ensures we'll notice the request to quit within 1s
if quit is signalled but there is not an udpate.
(I'm not sure if this happens or not)
I hate to make this such a large check but the lack of documentation means we really have no idea what's allowed. All of them reported so far have been within ".app/Contents" directories. That appears to be a safe starting point. However, I would not be surprised to also find more paths that are disallowed for instance in .framework or .bundle directories.
Fixes#2031Fixes#2229
This makes 'nix copy' and 'nix path-info' work on .drv store
paths. Removing special treatment of .drv files seems the most
future-proof approach given the possible removal of .drv files in the
future.
Note that 'nix build' will still build (rather than substitute) .drv
paths due to the unfortunate overloading in Store::buildPaths().
EvalState contains a few counters (e.g. nrValues) that increase
quickly enough that they end up being interpreted as pointers by the
garbage collector. Moving it to the heap makes them invisible to the
garbage collector.
This reduces the max RSS doing 100 evaluations of
nixos.tests.firefox.x86_64-linux.drvPath from 455 MiB to 292 MiB.
Note: ideally, allocations would be much further up in the 64-bit
address space to reduce the odds of an integer being misinterpreted as
a pointer. Maybe we can use some linker magic to move the .bss segment
to a higher address.
This reduces the risk of object liveness misdetection. For example,
Glibc has an internal variable "mp_" that often points to a Boehm
object, keeping it alive unnecessarily. Since we don't store any
actual roots in global variables, we can just disable data segment
scanning.
With this, the max RSS doing 100 evaluations of
nixos.tests.firefox.x86_64-linux.drvPath went from 718 MiB to 455 MiB.
If a process disappears between the time /proc/[pid]/maps is opened and
the time it is read, the read() syscall will return ESRCH. This should be ignored.
In some versions/configurations libcurl doesn't handle timeouts
(especially DNS timeouts) in a way that wakes curl_multi_wait.
This doesn't appear to be a problem if using c-ares, FWIW.
This reduces memory consumption of
nix copy --from file://... --to ~/my-nix /nix/store/95cwv4q54dc6giaqv6q6p4r02ia2km35-blender-2.79
from 514 MiB to 18 MiB for an uncompressed binary cache, and from 192
MiB to 53 MiB for a bzipped binary cache. It may also be faster
because fetching can happen concurrently with decompression/writing.
Continuation of 48662d151b.
Issue https://github.com/NixOS/nix/issues/1681.
Allow global config settings to be defined in multiple Config
classes. For example, this means that libutil can have settings and
evaluator settings can be moved out of libstore. The Config classes
are registered in a new GlobalConfig class to which config files
etc. are applied.
Relevant to https://github.com/NixOS/nix/issues/2009 in that it
removes the need for ad hoc handling of useCaseHack, which was the
underlying cause of that issue.
Continuation of 97002b684c. This makes
the daemon use constant memory. For example, it reduces the daemon's
maximum RSS on
$ nix copy --from ~/my-nix --to daemon /nix/store/1n7x0yv8vq6zi90hfmian84vdhd04bgp-blender-2.79a
from 264 MiB to 7 MiB.
We now use a TunnelSource to prevent the connection from ending up in
an undefined state if an exception is thrown while the NAR is being
sent.
Issue https://github.com/NixOS/nix/issues/1681.
If the Env denotes a 'with', then values[0] may be an Expr* cast to a
Value*. For code that generically traverses Values/Envs, it's useful
to know this.
E.g. this makes
nix eval --restrict-eval -I /nix/store/foo '(builtins.readFile "/nix/store/foo/symlink/bla")'
(where /nix/store/foo/symlink is a symlink to another path in the
closure of /nix/store/foo) succeed.
This fixes a regression in Hydra compared to Nix 1.x (where there were
no restrictions at all on access to the Nix store).
The existing ordering linked `libutil` before `libstore`, which causes
link failures when building statically. This is due to `libstore` using
functions from `libutil`, and the fact that symbol resolution works
"forward" - i.e. if you pass `-lfoo -lbar -lbaz`, any symbols that
`libbar` uses from `libbaz` will be resolved, but symbols from `libfoo`
will not since it comes first in the command line.
All this to say: this commit reorders the libraries which fixes the link
errors.
Don't bind-mount these to themselves,
mount them into the chroot directory.
Fixes pty issues when using sandbox on CentOS 7.4.
(build of perlPackages.IOTty fails before this change)
The common use case is to search for packages containing multiple words
like a "git" "frontend". Having only one expressions makes this simple regular
use case very complicated. Instead, search accepts multiple regular epressions
which all need to match.
nix search git 'gui|frontend'
returns a list of all git uis for example
Fixes
error: getting status of '/nix/store/j8p0vv89k1pf0cn7kmfsdcs7bshwga1i-firefox-52.7.2esr/share/icons/hicolor/48x48/apps/firefox.png': No such file or directory
https://github.com/NixOS/nix/issues/1934
Also improve error message on directory/non-directory collisions.
For instance, this reduced the memory consumption of
$ nix copy --from ssh://localhost --to ~/my-nix /nix/store/1n7x0yv8vq6zi90hfmian84vdhd04bgp-blender-2.79a
from 632 MiB to 16 MiB.
From exec(3):
> The list of arguments must be terminated by a null pointer, and, since these
> are variadic functions, this pointer must be cast (char *) NULL
E.g.
cannot build on 'ssh://mac1': cannot connect to 'mac1': bash: nix-store: command not found
cannot build on 'ssh://mac2': cannot connect to 'mac2': Host key verification failed.
cannot build on 'ssh://mac3': cannot connect to 'mac3': Received disconnect from 213... port 6001:2: Too many authentication failures
Authentication failed.
copyStorePath() now pipes the output of srcStore->narFromPath()
directly into dstStore->addToStore(). The sink used by the former is
converted into a source usable by the latter using
boost::coroutine2. This is based on [1].
This reduces the maximum resident size of
$ nix build --store ~/my-nix/ /nix/store/b0zlxla7dmy1iwc3g459rjznx59797xy-binutils-2.28.1 --substituters file:///tmp/binary-cache-xz/ --no-require-sigs
from 418592 KiB to 53416 KiB. (The previous commit also reduced the
runtime from ~4.2s to ~3.4s, not sure why.) A further improvement will
be to download files into a Sink.
[1] https://github.com/NixOS/nix/compare/master...Mathnerd314:dump-fix-coroutine#diff-dcbcac55a634031f9cc73707da6e4b18
Issue #1969.
It was holding on to a Value* (i.e. a std::shared_ptr<ValidPathInfo>*)
outside of the pathInfoCache lock, so the std::shared_ptr could be
destroyed between the release of the lock and the decrement of the
std::shared_ptr refcount. This can happen if more than
'path-info-cache-size' paths are added in the meantime, *or* if
clearPathInfoCache() is called. The hydra-queue-runner queue monitor
thread periodically calls the later, so is likely to trigger a crash.
Fixes https://github.com/NixOS/hydra/issues/542.
Doing so prevents emacs tags from working, as well as makes the code extremely
confusing for a newbie.
In the prior state, if someone wants to find the definition of "ExprApp" for
example, a grep through the code reveals nothing. Since the definition could be
hiding in numerous ".h" files, it's really difficult to find. This personally
took me several hours to figure out.
This can be iterated on and currently leaves out settings we know we
want to forward, but it fixes#1713 and fixes#1935 and isn't
fundamentally broken like the status quo. Future changes are suggested
in a comment.
Flex's regexes have an annoying feature: the dot matches everything
except a newline. This causes problems for expressions like:
"${0}\
"
where the backslash-newline combination matches this rule instead of the
intended one mentioned in the comment:
<STRING>\$|\\|\$\\ {
/* This can only occur when we reach EOF, otherwise the above
(...|\$[^\{\"\\]|\\.|\$\\.)+ would have triggered.
This is technically invalid, but we leave the problem to the
parser who fails with exact location. */
return STR;
}
However, the parser actually accepts the resulting token sequence
('"' DOLLAR_CURLY 0 '}' STR '"'), which is a problem because the lexer
rule didn't assign anything to yylval. Ultimately this leads to a crash
when dereferencing a NULL pointer in ExprConcatStrings::bindVars().
The fix does change the syntax of the language in some corner cases
but I think it's only turning previously invalid (or crashing) syntax
to valid syntax. E.g.
"a\
b"
and
''a''\
b''
were previously syntax errors but now both result in "a\nb".
Found by afl-fuzz.
This allows building armv[67]l-linux derivations on compatible aarch64
machines. Failure to add the architecture may result from missing
hardware support, in which case we can't run 32-bit binaries and don't
need to restrict them with seccomp anyway,
This allows specifying additional systems that a machine is able to
build for. This may apply on some armv7-capable aarch64 processors, or
on systems using qemu-user with binfmt-misc to support transparent
execution of foreign-arch programs.
This removes the previous hard-coded assumptions about which systems are
ABI-compatible with which other systems, and instead relies on the user
to specify any additional platforms that they have ensured compatibility
for and wish to build for locally.
NixOS should probably add i686-linux on x86_64-linux systems for this
setting by default.
Otherwise, running e.g.
nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'
would just hang in an infinite loop.
Found by afl-fuzz.
First attempt of this was reverted in e2d71bd186 because it caused
another infinite loop, which is fixed now and a test added.
This is important since this is given as an example.
Other patterns containing "empty search string" will still
be handled differently on different platforms ("asdf|")
but that's less of an issue.
The overhead of sandbox builds is a problem on NixOS (since building a
NixOS configuration involves a lot of small derivations) but not for
typical non-NixOS use cases. So outside of NixOS we can enable it.
Issue #179.
The assertion is broken because there is no one-to-one mapping from
length of a base64 string to the length of the output.
E.g.
"1q69lz7Empb06nzfkj651413n9icx0njmyr3xzq1j9q=" results in a 32-byte output.
"1q69lz7Empb06nzfkj651413n9icx0njmyr3xzq1j9qy" results in a 33-byte output.
To reproduce, evaluate:
builtins.derivationStrict {
name = "0";
builder = "0";
system = "0";
outputHashAlgo = "sha256";
outputHash = "1q69lz7Empb06nzfkj651413n9icx0njmyr3xzq1j9qy";
}
Found by afl-fuzz.
Otherwise, running e.g.
nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'
would just hang in an infinite loop.
Found by afl-fuzz.
Instead of having lexicographicOrder() create a temporary sorted array
of Attr*:s and copying attr names from that, copy the attr names
first and then sort that.
Previously, this would fail at startup for non-NixOS installs:
nix-env --help
The fix for this is to just use "nixManDir" as the value for MANPATH
when spawning "man".
To test this, I’m using the following:
$ nix-build release.nix -A build
$ MANPATH= ./result/bin/nix-env --help
Fixes#1627
nix-store --export, nix-store --dump, and nix dump-path would previously
fail silently if writing the data out failed, because
a) FdSink::write ignored exceptions, and
b) the commands relied on FdSink's destructor, which ignores
exceptions, to flush the data out.
This could cause rather opaque issues with installing nixos, because
nix-store --export would happily proceed even if it couldn't write its
data out (e.g. if nix-store --import on the other side of the pipe
failed).
This commit adds tests that expose these issues in the nix-store
commands, and fixes them for all three.
This was caused by derivations with 'allowSubstitutes = false'. Such
derivations will be built locally. However, if there is another
SubstitionGoal that has the output of the first derivation in its
closure, then the path will be simultaneously built and substituted.
There was a check to catch this situation (via pathIsLockedByMe()),
but it no longer worked reliably because substitutions are now done in
another thread. (Thus the comment 'It can't happen between here and
the lockPaths() call below because we're not allowing multi-threading'
was no longer valid.)
The fix is to handle the path already being locked in both
SubstitutionGoal and DerivationGoal.
All ANSI sequences except color setting are now filtered out. In
particular, terminal resets (such as from NixOS VM tests) are filtered
out.
Also, fix the completely broken tab character handling.
builtins.path allows specifying the name of a path (which makes paths
with store-illegal names now addable), allows adding paths with flat
instead of recursive hashes, allows specifying a filter (so is a
generalization of filterSource), and allows specifying an expected
hash (enabling safe path adding in pure mode).
the case of hydra where the overhead of single threaded encoding is more
noticeable e.g most of the time spent in "Sending inputs"/"Receiving outputs"
is due to compression while the actual upload to the binary cache seems
to be negligible.
This is needed by nixos-install, which uses the Nix store on the
installation CD as a substituter. We don't want to disable signature
checking entirely because substitutes from cache.nixos.org should
still be checked. So now we can pas "local?trusted=1" to mark only the
Nix store in /nix as not requiring signatures.
Fixes#1819.
Instead, if a fixed-output derivation produces has an incorrect output
hash, we now unconditionally move the outputs to the path
corresponding with the actual hash and register it as valid. Thus,
after correcting the hash in the Nix expression (e.g. in a fetchurl
call), the fixed-output derivation doesn't have to be built again.
It would still be good to have a command for reporting the actual hash
of a fixed-output derivation (instead of throwing an error), but
"nix-build --hash" didn't do that.
Following discussion with Shea and Graham. It's a big enough change
from the last release. Also, from a semver perspective, 2.0 makes more
sense because we did remove some interfaces (like nix-pull/nix-push).
Some servers, such as Artifactory, allow uploading with PUT and BASIC
auth. This allows nix copy to work to upload binaries to those
servers.
Worked on together with @adelbertc
In this mode, the following restrictions apply:
* The builtins currentTime, currentSystem and storePath throw an
error.
* $NIX_PATH and -I are ignored.
* fetchGit and fetchMercurial require a revision hash.
* fetchurl and fetchTarball require a sha256 attribute.
* No file system access is allowed outside of the paths returned by
fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
not allowed.
Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.
nix build --pure-eval '(
let
nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
)'
The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like
nix build --pure-eval '(
(import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
')
where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
* Look for both 'brotli' and 'bro' as external command,
since upstream has renamed it in newer versions.
If neither are found, current runtime behavior
is preserved: try to find 'bro' on PATH.
* Limit amount handed to BrotliEncoderCompressStream
to ensure interrupts are processed in a timely manner.
Testing shows negligible performance impact.
(Other compression sinks don't seem to require this)
E.g.
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nars \
/nix/store/b0w2hafndl09h64fhb86kw6bmhbmnpm1-blender-2.79/share/icons/hicolor/scalable/apps/blender.svg > /dev/null
real 0m4.139s
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nars \
/nix/store/b0w2hafndl09h64fhb86kw6bmhbmnpm1-blender-2.79/share/icons/hicolor/scalable/apps/blender.svg > /dev/null
real 0m0.024s
(Before, the second call took ~0.220s.)
This will use a NAR listing in
/tmp/nars/b0w2hafndl09h64fhb86kw6bmhbmnpm1.ls containing all metadata,
including the offsets of regular files inside the NAR. Thus, we don't
need to read the entire NAR. (We do read the entire listing, but
that's generally pretty small. We could use a SQLite DB by borrowing
some more code from nixos-channel-scripts/file-cache.hh.)
This is primarily useful when Hydra is serving files from an S3 binary
cache, in particular when you have giant NARs. E.g. we had some 12 GiB
NARs, so accessing individuals files was pretty slow.
propagated-user-env-packages files in nixpkgs aren't all terminated by
newlines, as buildenv expected. Now it does not require a terminating
newline; note that this introduces a behaviour change: propagated user
env packages may now be spread across multiple lines. However, nix
1.11.x still expects them to be on a single line so this shouldn't be
used in nixpkgs for now.
The storeUri variable in the build-remote hook is declared very much to
the start of the main function and a bunch of lines later, the same
variable gets checked via hasPrefix() but it gets assigned *after* that
check when the most suitable machine for the build was choosen.
So I guess this was just a typo in d16fd24973
and what we really want is to either checkd the prefix *after* assigning
storeUri or use bestMachine->storeUri directly.
I choose the latter, because the former could introduce even more
regressions if the try block where the variable gets assigned terminates
early.
Nevertheless, the reason why the log output didn't work is because
hasPrefix() checked for "ssh://" in front of storeUri, but if the
storeUri isn't set correctly (or at all), we don't get the log file
descriptor set up properly, leading to no log output.
I've adjusted the remote-builds test to include a regression test for
this, so that we can make sure we get a build output when using remote
builds.
In addition to that I've tested this with two of my build farms and the
build logs are emitted correctly again.
Signed-off-by: aszlig <aszlig@nix.build>
The name had become a misnomer since it's not only for substitution
from binary caches, but when adding/copying any
(non-content-addressed) path to a store.
This allows specifying the AWS configuration profile to use. E.g.
nix copy --from s3://my-cache?profile=aws-dev-account /nix/store/cf3isrlqavvd5w7rpky1fa8j9lcnlggm-...
As far as we're concerned, not being able to access a file just means
the file is missing. Plus, AWS explicitly goes out of its way to
return a 403 if the file is missing and the requester doesn't have
permission to list the bucket.
Also getting rid of an old hack that Eelco said was only relevant
to an older AWS SDK.
For example, you can write
src = fetchgit ./.;
and if ./. refers to an unclean working tree, that tree will be copied
to the Nix store. This removes the need for "cleanSource".
This will allow bind and connect to 127.0.0.1, which can reduce purity/
security (if you're running a vulnerable service on localhost) but is
also needed for a ton of test suites, so I'm leaving it turned off by
default but allowing certain derivations to turn it on as needed.
It also allows DNS resolution of arbitrary hostnames but I haven't found
a way to avoid that. In principle I'd just want to allow resolving
localhost but that doesn't seem to be possible.
I don't think this belongs under `build-use-sandbox = relaxed` because we
want it on Hydra and I don't think it's the end of the world.
Used to determine symlink size with stat and value with readlink.
This could technically result in garbage if symlink changed between
calls. Also gets around the broken stat implementation in our
network filesystem (returns size + 1 giving a byte of garbage).
The computation of urlHash didn't take the name into account, so
subsequent fetchurl calls with the same URL but a different name would
resolve to the same cached store path.
The "name" attribute defaults to "source", which we should use for all
similar functions (e.g. fetchTarball and in Hydra) to ensure that we
get a consistent store path regardless of how the tree is fetched.
"source" is not necessarily a correct label, but using an empty name
is problematic: you get an ugly store path ending in a dash, and it's
impossible to have a fixed-output derivation that produces that path
because ".drv" is not a valid store name.
Fixes#904.
You can now include files via the "builders" option, using the syntax
"@<filename>". Having only one option makes it easier to override
builders completely.
For backward compatibility, the default is "@/etc/nix/machines", or
"@<filename>" for each file name in NIX_REMOTE_SYSTEMS.
