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11
doc/manual/src/SUMMARY.md
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- [Command Reference](command-ref/command-ref.md)
- [Common Options](command-ref/opt-common.md)
- [Common Environment Variables](command-ref/env-common.md)
- [Main Commands](command-ref/main-commands.md)
- [nix-env](command-ref/nix-env.md)
- [nix-build](command-ref/nix-build.md)
- [nix-shell](command-ref/nix-shell.md)
- [nix-store](command-ref/nix-store.md)
- [Utilities](command-ref/utilities.md)
- [nix-channel](command-ref/nix-channel.md)
- [nix-collect-garbage](command-ref/nix-collect-garbage.md)
- [nix-copy-closure](command-ref/nix-copy-closure.md)
- [nix-daemon](command-ref/nix-daemon.md)
- [nix-hash](command-ref/nix-hash.md)
- [nix-instantiate](command-ref/nix-instantiate.md)
- [nix-prefetch-url](command-ref/nix-prefetch-url.md)
- [Files](command-ref/files.md)
- [nix.conf](command-ref/conf-file.md)
- [Glossary](glossary.md)

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# Command Reference
This section lists commands and options that you can use when you
work with Nix.
This section lists commands and options that you can use when you work
with Nix.

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# Main Commands
This section lists commands and options that you can use when you work
with Nix.

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nix-build
1
Nix
nix-build
build a Nix expression
nix-build
\--arg
name
value
\--argstr
name
value
\--attr
\-A
attrPath
\--no-out-link
\--dry-run
\--out-link
\-o
outlink
paths
# Description
The `nix-build` command builds the derivations described by the Nix
expressions in paths. If the build succeeds, it places a symlink to the
result in the current directory. The symlink is called `result`. If
there are multiple Nix expressions, or the Nix expressions evaluate to
multiple derivations, multiple sequentially numbered symlinks are
created (`result`, `result-2`, and so on).
If no paths are specified, then `nix-build` will use `default.nix` in
the current directory, if it exists.
If an element of paths starts with `http://` or `https://`, it is
interpreted as the URL of a tarball that will be downloaded and unpacked
to a temporary location. The tarball must include a single top-level
directory containing at least a file named `default.nix`.
`nix-build` is essentially a wrapper around
[`nix-instantiate`](#sec-nix-instantiate) (to translate a high-level Nix
expression to a low-level store derivation) and [`nix-store
--realise`](#rsec-nix-store-realise) (to build the store derivation).
> **Warning**
>
> The result of the build is automatically registered as a root of the
> Nix garbage collector. This root disappears automatically when the
> `result` symlink is deleted or renamed. So don’t rename the symlink.
# Options
All options not listed here are passed to `nix-store
--realise`, except for `--arg` and `--attr` / `-A` which are passed to
`nix-instantiate`. See also [???](#sec-common-options).
- `--no-out-link`
Do not create a symlink to the output path. Note that as a result
the output does not become a root of the garbage collector, and so
might be deleted by `nix-store
--gc`.
- `--dry-run`
Show what store paths would be built or downloaded.
- `--out-link` / `-o` outlink
Change the name of the symlink to the output path created from
`result` to outlink.
The following common options are supported:
# Examples
$ nix-build '<nixpkgs>' -A firefox
store derivation is /nix/store/qybprl8sz2lc...-firefox-1.5.0.7.drv
/nix/store/d18hyl92g30l...-firefox-1.5.0.7
$ ls -l result
lrwxrwxrwx ... result -> /nix/store/d18hyl92g30l...-firefox-1.5.0.7
$ ls ./result/bin/
firefox firefox-config
If a derivation has multiple outputs, `nix-build` will build the default
(first) output. You can also build all outputs:
$ nix-build '<nixpkgs>' -A openssl.all
This will create a symlink for each output named `result-outputname`.
The suffix is omitted if the output name is `out`. So if `openssl` has
outputs `out`, `bin` and `man`, `nix-build` will create symlinks
`result`, `result-bin` and `result-man`. It’s also possible to build a
specific output:
$ nix-build '<nixpkgs>' -A openssl.man
This will create a symlink `result-man`.
Build a Nix expression given on the command line:
$ nix-build -E 'with import <nixpkgs> { }; runCommand "foo" { } "echo bar > $out"'
$ cat ./result
bar
Build the GNU Hello package from the latest revision of the master
branch of Nixpkgs:
$ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz -A hello
# Environment variables

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nix-channel
1
Nix
nix-channel
manage Nix channels
nix-channel
\--add
url
name
\--remove
name
\--list
\--update
names
\--rollback
generation
# Description
A Nix channel is a mechanism that allows you to automatically stay
up-to-date with a set of pre-built Nix expressions. A Nix channel is
just a URL that points to a place containing a set of Nix expressions.
See also [???](#sec-channels).
To see the list of official NixOS channels, visit
<https://nixos.org/channels>.
This command has the following operations:
- `--add` url \[name\]
Adds a channel named name with URL url to the list of subscribed
channels. If name is omitted, it defaults to the last component of
url, with the suffixes `-stable` or `-unstable` removed.
- `--remove` name
Removes the channel named name from the list of subscribed channels.
- `--list`
Prints the names and URLs of all subscribed channels on standard
output.
- `--update` \[names…\]
Downloads the Nix expressions of all subscribed channels (or only
those included in names if specified) and makes them the default for
`nix-env` operations (by symlinking them from the directory
`~/.nix-defexpr`).
- `--rollback` \[generation\]
Reverts the previous call to `nix-channel
--update`. Optionally, you can specify a specific channel generation
number to restore.
Note that `--add` does not automatically perform an update.
The list of subscribed channels is stored in `~/.nix-channels`.
# Examples
To subscribe to the Nixpkgs channel and install the GNU Hello package:
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
$ nix-channel --update
$ nix-env -iA nixpkgs.hello
You can revert channel updates using `--rollback`:
$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
"14.04.527.0e935f1"
$ nix-channel --rollback
switching from generation 483 to 482
$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
"14.04.526.dbadfad"
# Files
- `/nix/var/nix/profiles/per-user/username/channels`
`nix-channel` uses a `nix-env` profile to keep track of previous
versions of the subscribed channels. Every time you run `nix-channel
--update`, a new channel generation (that is, a symlink to the
channel Nix expressions in the Nix store) is created. This enables
`nix-channel --rollback` to revert to previous versions.
- `~/.nix-defexpr/channels`
This is a symlink to
`/nix/var/nix/profiles/per-user/username/channels`. It ensures that
`nix-env` can find your channels. In a multi-user installation, you
may also have `~/.nix-defexpr/channels_root`, which links to the
channels of the root user.
# Channel format
A channel URL should point to a directory containing the following
files:
- `nixexprs.tar.xz`
A tarball containing Nix expressions and files referenced by them
(such as build scripts and patches). At the top level, the tarball
should contain a single directory. That directory must contain a
file `default.nix` that serves as the channel’s “entry point”.

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nix-collect-garbage
1
Nix
nix-collect-garbage
delete unreachable store paths
nix-collect-garbage
\--delete-old
\-d
\--delete-older-than
period
\--max-freed
bytes
\--dry-run
# Description
The command `nix-collect-garbage` is mostly an alias of [`nix-store
--gc`](#rsec-nix-store-gc), that is, it deletes all unreachable paths in
the Nix store to clean up your system. However, it provides two
additional options: `-d` (`--delete-old`), which deletes all old
generations of all profiles in `/nix/var/nix/profiles` by invoking
`nix-env --delete-generations old` on all profiles (of course, this
makes rollbacks to previous configurations impossible); and
`--delete-older-than` period, where period is a value such as `30d`,
which deletes all generations older than the specified number of days in
all profiles in `/nix/var/nix/profiles` (except for the generations that
were active at that point in time).
# Example
To delete from the Nix store everything that is not used by the current
generations of each profile, do
$ nix-collect-garbage -d

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nix-daemon
8
Nix
nix-daemon
Nix multi-user support daemon
nix-daemon
# Description
The Nix daemon is necessary in multi-user Nix installations. It performs
build actions and other operations on the Nix store on behalf of
unprivileged users.

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nix-env
1
Nix
nix-env
manipulate or query Nix user environments
nix-env
\--arg
name
value
\--argstr
name
value
\--file
\-f
path
\--profile
\-p
path
\--system-filter
system
\--dry-run
operation
options
arguments
# Description
The command `nix-env` is used to manipulate Nix user environments. User
environments are sets of software packages available to a user at some
point in time. In other words, they are a synthesised view of the
programs available in the Nix store. There may be many user
environments: different users can have different environments, and
individual users can switch between different environments.
`nix-env` takes exactly one *operation* flag which indicates the
subcommand to be performed. These are documented below.
# Selectors
Several commands, such as `nix-env -q` and `nix-env -i`, take a list of
arguments that specify the packages on which to operate. These are
extended regular expressions that must match the entire name of the
package. (For details on regular expressions, see regex7.) The match is
case-sensitive. The regular expression can optionally be followed by a
dash and a version number; if omitted, any version of the package will
match. Here are some examples:
- `firefox`
Matches the package name `firefox` and any version.
- `firefox-32.0`
Matches the package name `firefox` and version `32.0`.
- `gtk\\+`
Matches the package name `gtk+`. The `+` character must be escaped
using a backslash to prevent it from being interpreted as a
quantifier, and the backslash must be escaped in turn with another
backslash to ensure that the shell passes it on.
- `.\*`
Matches any package name. This is the default for most commands.
- `'.*zip.*'`
Matches any package name containing the string `zip`. Note the dots:
`'*zip*'` does not work, because in a regular expression, the
character `*` is interpreted as a quantifier.
- `'.*(firefox|chromium).*'`
Matches any package name containing the strings `firefox` or
`chromium`.
# Common options
This section lists the options that are common to all operations. These
options are allowed for every subcommand, though they may not always
have an effect. See also [???](#sec-common-options).
- `--file` / `-f` path
Specifies the Nix expression (designated below as the *active Nix
expression*) used by the `--install`, `--upgrade`, and `--query
--available` operations to obtain derivations. The default is
`~/.nix-defexpr`.
If the argument starts with `http://` or `https://`, it is
interpreted as the URL of a tarball that will be downloaded and
unpacked to a temporary location. The tarball must include a single
top-level directory containing at least a file named `default.nix`.
- `--profile` / `-p` path
Specifies the profile to be used by those operations that operate on
a profile (designated below as the *active profile*). A profile is a
sequence of user environments called *generations*, one of which is
the *current generation*.
- `--dry-run`
For the `--install`, `--upgrade`, `--uninstall`,
`--switch-generation`, `--delete-generations` and `--rollback`
operations, this flag will cause `nix-env` to print what *would* be
done if this flag had not been specified, without actually doing it.
`--dry-run` also prints out which paths will be
[substituted](#gloss-substitute) (i.e., downloaded) and which paths
will be built from source (because no substitute is available).
- `--system-filter` system
By default, operations such as `--query
--available` show derivations matching any platform. This option
allows you to use derivations for the specified platform system.
<!-- end list -->
# Files
- `~/.nix-defexpr`
The source for the default Nix expressions used by the `--install`,
`--upgrade`, and `--query
--available` operations to obtain derivations. The `--file` option
may be used to override this default.
If `~/.nix-defexpr` is a file, it is loaded as a Nix expression. If
the expression is a set, it is used as the default Nix expression.
If the expression is a function, an empty set is passed as argument
and the return value is used as the default Nix expression.
If `~/.nix-defexpr` is a directory containing a `default.nix` file,
that file is loaded as in the above paragraph.
If `~/.nix-defexpr` is a directory without a `default.nix` file,
then its contents (both files and subdirectories) are loaded as Nix
expressions. The expressions are combined into a single set, each
expression under an attribute with the same name as the original
file or subdirectory.
For example, if `~/.nix-defexpr` contains two files, `foo.nix` and
`bar.nix`, then the default Nix expression will essentially be
{
foo = import ~/.nix-defexpr/foo.nix;
bar = import ~/.nix-defexpr/bar.nix;
}
The file `manifest.nix` is always ignored. Subdirectories without a
`default.nix` file are traversed recursively in search of more Nix
expressions, but the names of these intermediate directories are not
added to the attribute paths of the default Nix expression.
The command `nix-channel` places symlinks to the downloaded Nix
expressions from each subscribed channel in this directory.
- `~/.nix-profile`
A symbolic link to the user's current profile. By default, this
symlink points to `prefix/var/nix/profiles/default`. The `PATH`
environment variable should include `~/.nix-profile/bin` for the
user environment to be visible to the user.
# Operation `--install`
## Synopsis
nix-env
\--install
\-i
\--preserve-installed
\-P
\--remove-all
\-r
args
## Description
The install operation creates a new user environment, based on the
current generation of the active profile, to which a set of store paths
described by args is added. The arguments args map to store paths in a
number of possible ways:
- By default, args is a set of derivation names denoting derivations
in the active Nix expression. These are realised, and the resulting
output paths are installed. Currently installed derivations with a
name equal to the name of a derivation being added are removed
unless the option `--preserve-installed` is specified.
If there are multiple derivations matching a name in args that have
the same name (e.g., `gcc-3.3.6` and `gcc-4.1.1`), then the
derivation with the highest *priority* is used. A derivation can
define a priority by declaring the `meta.priority` attribute. This
attribute should be a number, with a higher value denoting a lower
priority. The default priority is `0`.
If there are multiple matching derivations with the same priority,
then the derivation with the highest version will be installed.
You can force the installation of multiple derivations with the same
name by being specific about the versions. For instance, `nix-env -i
gcc-3.3.6 gcc-4.1.1` will install both version of GCC (and will
probably cause a user environment conflict\!).
- If [`--attr`](#opt-attr) (`-A`) is specified, the arguments are
*attribute paths* that select attributes from the top-level Nix
expression. This is faster than using derivation names and
unambiguous. To find out the attribute paths of available packages,
use `nix-env -qaP`.
- If `--from-profile` path is given, args is a set of names denoting
installed store paths in the profile path. This is an easy way to
copy user environment elements from one profile to another.
- If `--from-expression` is given, args are Nix
[functions](#ss-functions) that are called with the active Nix
expression as their single argument. The derivations returned by
those function calls are installed. This allows derivations to be
specified in an unambiguous way, which is necessary if there are
multiple derivations with the same name.
- If args are store derivations, then these are
[realised](#rsec-nix-store-realise), and the resulting output paths
are installed.
- If args are store paths that are not store derivations, then these
are [realised](#rsec-nix-store-realise) and installed.
- By default all outputs are installed for each derivation. That can
be reduced by setting `meta.outputsToInstall`.
## Flags
- `--prebuilt-only` / `-b`
Use only derivations for which a substitute is registered, i.e.,
there is a pre-built binary available that can be downloaded in lieu
of building the derivation. Thus, no packages will be built from
source.
- `--preserve-installed`; `-P`
Do not remove derivations with a name matching one of the
derivations being installed. Usually, trying to have two versions of
the same package installed in the same generation of a profile will
lead to an error in building the generation, due to file name
clashes between the two versions. However, this is not the case for
all packages.
- `--remove-all`; `-r`
Remove all previously installed packages first. This is equivalent
to running `nix-env -e '.*'` first, except that everything happens
in a single transaction.
## Examples
To install a specific version of `gcc` from the active Nix expression:
$ nix-env --install gcc-3.3.2
installing `gcc-3.3.2'
uninstalling `gcc-3.1'
Note the previously installed version is removed, since
`--preserve-installed` was not specified.
To install an arbitrary version:
$ nix-env --install gcc
installing `gcc-3.3.2'
To install using a specific attribute:
$ nix-env -i -A gcc40mips
$ nix-env -i -A xorg.xorgserver
To install all derivations in the Nix expression `foo.nix`:
$ nix-env -f ~/foo.nix -i '.*'
To copy the store path with symbolic name `gcc` from another profile:
$ nix-env -i --from-profile /nix/var/nix/profiles/foo gcc
To install a specific store derivation (typically created by
`nix-instantiate`):
$ nix-env -i /nix/store/fibjb1bfbpm5mrsxc4mh2d8n37sxh91i-gcc-3.4.3.drv
To install a specific output path:
$ nix-env -i /nix/store/y3cgx0xj1p4iv9x0pnnmdhr8iyg741vk-gcc-3.4.3
To install from a Nix expression specified on the command-line:
$ nix-env -f ./foo.nix -i -E \
'f: (f {system = "i686-linux";}).subversionWithJava'
I.e., this evaluates to `(f: (f {system =
"i686-linux";}).subversionWithJava) (import ./foo.nix)`, thus selecting
the `subversionWithJava` attribute from the set returned by calling the
function defined in `./foo.nix`.
A dry-run tells you which paths will be downloaded or built from source:
$ nix-env -f '<nixpkgs>' -iA hello --dry-run
(dry run; not doing anything)
installing ‘hello-2.10’
this path will be fetched (0.04 MiB download, 0.19 MiB unpacked):
/nix/store/wkhdf9jinag5750mqlax6z2zbwhqb76n-hello-2.10
...
To install Firefox from the latest revision in the Nixpkgs/NixOS 14.12
channel:
$ nix-env -f https://github.com/NixOS/nixpkgs/archive/nixos-14.12.tar.gz -iA firefox
# Operation `--upgrade`
## Synopsis
nix-env
\--upgrade
\-u
\--lt
\--leq
\--eq
\--always
args
## Description
The upgrade operation creates a new user environment, based on the
current generation of the active profile, in which all store paths are
replaced for which there are newer versions in the set of paths
described by args. Paths for which there are no newer versions are left
untouched; this is not an error. It is also not an error if an element
of args matches no installed derivations.
For a description of how args is mapped to a set of store paths, see
[`--install`](#rsec-nix-env-install). If args describes multiple store
paths with the same symbolic name, only the one with the highest version
is installed.
## Flags
- `--lt`
Only upgrade a derivation to newer versions. This is the default.
- `--leq`
In addition to upgrading to newer versions, also “upgrade” to
derivations that have the same version. Version are not a unique
identification of a derivation, so there may be many derivations
that have the same version. This flag may be useful to force
“synchronisation” between the installed and available derivations.
- `--eq`
*Only* “upgrade” to derivations that have the same version. This may
not seem very useful, but it actually is, e.g., when there is a new
release of Nixpkgs and you want to replace installed applications
with the same versions built against newer dependencies (to reduce
the number of dependencies floating around on your system).
- `--always`
In addition to upgrading to newer versions, also “upgrade” to
derivations that have the same or a lower version. I.e., derivations
may actually be downgraded depending on what is available in the
active Nix expression.
For the other flags, see `--install`.
## Examples
$ nix-env --upgrade gcc
upgrading `gcc-3.3.1' to `gcc-3.4'
$ nix-env -u gcc-3.3.2 --always (switch to a specific version)
upgrading `gcc-3.4' to `gcc-3.3.2'
$ nix-env --upgrade pan
(no upgrades available, so nothing happens)
$ nix-env -u (try to upgrade everything)
upgrading `hello-2.1.2' to `hello-2.1.3'
upgrading `mozilla-1.2' to `mozilla-1.4'
## Versions
The upgrade operation determines whether a derivation `y` is an upgrade
of a derivation `x` by looking at their respective `name` attributes.
The names (e.g., `gcc-3.3.1` are split into two parts: the package name
(`gcc`), and the version (`3.3.1`). The version part starts after the
first dash not followed by a letter. `x` is considered an upgrade of `y`
if their package names match, and the version of `y` is higher that that
of `x`.
The versions are compared by splitting them into contiguous components
of numbers and letters. E.g., `3.3.1pre5` is split into `[3, 3, 1,
"pre", 5]`. These lists are then compared lexicographically (from left
to right). Corresponding components `a` and `b` are compared as follows.
If they are both numbers, integer comparison is used. If `a` is an empty
string and `b` is a number, `a` is considered less than `b`. The special
string component `pre` (for *pre-release*) is considered to be less than
other components. String components are considered less than number
components. Otherwise, they are compared lexicographically (i.e., using
case-sensitive string comparison).
This is illustrated by the following examples:
1.0 < 2.3
2.1 < 2.3
2.3 = 2.3
2.5 > 2.3
3.1 > 2.3
2.3.1 > 2.3
2.3.1 > 2.3a
2.3pre1 < 2.3
2.3pre3 < 2.3pre12
2.3a < 2.3c
2.3pre1 < 2.3c
2.3pre1 < 2.3q
# Operation `--uninstall`
## Synopsis
nix-env
\--uninstall
\-e
drvnames
## Description
The uninstall operation creates a new user environment, based on the
current generation of the active profile, from which the store paths
designated by the symbolic names names are removed.
## Examples
$ nix-env --uninstall gcc
$ nix-env -e '.*' (remove everything)
# Operation `--set`
## Synopsis
nix-env
\--set
drvname
## Description
The `--set` operation modifies the current generation of a profile so
that it contains exactly the specified derivation, and nothing else.
## Examples
The following updates a profile such that its current generation will
contain just Firefox:
$ nix-env -p /nix/var/nix/profiles/browser --set firefox
# Operation `--set-flag`
## Synopsis
nix-env
\--set-flag
name
value
drvnames
## Description
The `--set-flag` operation allows meta attributes of installed packages
to be modified. There are several attributes that can be usefully
modified, because they affect the behaviour of `nix-env` or the user
environment build script:
- `priority` can be changed to resolve filename clashes. The user
environment build script uses the `meta.priority` attribute of
derivations to resolve filename collisions between packages. Lower
priority values denote a higher priority. For instance, the GCC
wrapper package and the Binutils package in Nixpkgs both have a file
`bin/ld`, so previously if you tried to install both you would get a
collision. Now, on the other hand, the GCC wrapper declares a higher
priority than Binutils, so the former’s `bin/ld` is symlinked in the
user environment.
- `keep` can be set to `true` to prevent the package from being
upgraded or replaced. This is useful if you want to hang on to an
older version of a package.
- `active` can be set to `false` to “disable” the package. That is, no
symlinks will be generated to the files of the package, but it
remains part of the profile (so it won’t be garbage-collected). It
can be set back to `true` to re-enable the package.
## Examples
To prevent the currently installed Firefox from being upgraded:
$ nix-env --set-flag keep true firefox
After this, `nix-env -u` will ignore Firefox.
To disable the currently installed Firefox, then install a new Firefox
while the old remains part of the profile:
$ nix-env -q
firefox-2.0.0.9 (the current one)
$ nix-env --preserve-installed -i firefox-2.0.0.11
installing `firefox-2.0.0.11'
building path(s) `/nix/store/myy0y59q3ig70dgq37jqwg1j0rsapzsl-user-environment'
collision between `/nix/store/...-firefox-2.0.0.11/bin/firefox'
and `/nix/store/...-firefox-2.0.0.9/bin/firefox'.
(i.e., can’t have two active at the same time)
$ nix-env --set-flag active false firefox
setting flag on `firefox-2.0.0.9'
$ nix-env --preserve-installed -i firefox-2.0.0.11
installing `firefox-2.0.0.11'
$ nix-env -q
firefox-2.0.0.11 (the enabled one)
firefox-2.0.0.9 (the disabled one)
To make files from `binutils` take precedence over files from `gcc`:
$ nix-env --set-flag priority 5 binutils
$ nix-env --set-flag priority 10 gcc
# Operation `--query`
## Synopsis
nix-env
\--query
\-q
\--installed
\--available
\-a
\--status
\-s
\--attr-path
\-P
\--no-name
\--compare-versions
\-c
\--system
\--drv-path
\--out-path
\--description
\--meta
\--xml
\--json
\--prebuilt-only
\-b
\--attr
\-A
attribute-path
names
## Description
The query operation displays information about either the store paths
that are installed in the current generation of the active profile
(`--installed`), or the derivations that are available for installation
in the active Nix expression (`--available`). It only prints information
about derivations whose symbolic name matches one of names.
The derivations are sorted by their `name` attributes.
## Source selection
The following flags specify the set of things on which the query
operates.
- `--installed`
The query operates on the store paths that are installed in the
current generation of the active profile. This is the default.
- `--available`; `-a`
The query operates on the derivations that are available in the
active Nix expression.
## Queries
The following flags specify what information to display about the
selected derivations. Multiple flags may be specified, in which case the
information is shown in the order given here. Note that the name of the
derivation is shown unless `--no-name` is specified.
- `--xml`
Print the result in an XML representation suitable for automatic
processing by other tools. The root element is called `items`, which
contains a `item` element for each available or installed
derivation. The fields discussed below are all stored in attributes
of the `item` elements.
- `--json`
Print the result in a JSON representation suitable for automatic
processing by other tools.
- `--prebuilt-only` / `-b`
Show only derivations for which a substitute is registered, i.e.,
there is a pre-built binary available that can be downloaded in lieu
of building the derivation. Thus, this shows all packages that
probably can be installed quickly.
- `--status`; `-s`
Print the *status* of the derivation. The status consists of three
characters. The first is `I` or `-`, indicating whether the
derivation is currently installed in the current generation of the
active profile. This is by definition the case for `--installed`,
but not for `--available`. The second is `P` or `-`, indicating
whether the derivation is present on the system. This indicates
whether installation of an available derivation will require the
derivation to be built. The third is `S` or `-`, indicating whether
a substitute is available for the derivation.
- `--attr-path`; `-P`
Print the *attribute path* of the derivation, which can be used to
unambiguously select it using the [`--attr` option](#opt-attr)
available in commands that install derivations like `nix-env
--install`. This option only works together with `--available`
- `--no-name`
Suppress printing of the `name` attribute of each derivation.
- `--compare-versions` / `-c`
Compare installed versions to available versions, or vice versa (if
`--available` is given). This is useful for quickly seeing whether
upgrades for installed packages are available in a Nix expression. A
column is added with the following meaning:
- `<` version
A newer version of the package is available or installed.
- `=` version
At most the same version of the package is available or
installed.
- `>` version
Only older versions of the package are available or installed.
- `- ?`
No version of the package is available or installed.
- `--system`
Print the `system` attribute of the derivation.
- `--drv-path`
Print the path of the store derivation.
- `--out-path`
Print the output path of the derivation.
- `--description`
Print a short (one-line) description of the derivation, if
available. The description is taken from the `meta.description`
attribute of the derivation.
- `--meta`
Print all of the meta-attributes of the derivation. This option is
only available with `--xml` or `--json`.
## Examples
To show installed packages:
$ nix-env -q
bison-1.875c
docbook-xml-4.2
firefox-1.0.4
MPlayer-1.0pre7
ORBit2-2.8.3
…
To show available packages:
$ nix-env -qa
firefox-1.0.7
GConf-2.4.0.1
MPlayer-1.0pre7
ORBit2-2.8.3
…
To show the status of available packages:
$ nix-env -qas
-P- firefox-1.0.7 (not installed but present)
--S GConf-2.4.0.1 (not present, but there is a substitute for fast installation)
--S MPlayer-1.0pre3 (i.e., this is not the installed MPlayer, even though the version is the same!)
IP- ORBit2-2.8.3 (installed and by definition present)
…
To show available packages in the Nix expression `foo.nix`:
$ nix-env -f ./foo.nix -qa
foo-1.2.3
To compare installed versions to what’s available:
$ nix-env -qc
...
acrobat-reader-7.0 - ? (package is not available at all)
autoconf-2.59 = 2.59 (same version)
firefox-1.0.4 < 1.0.7 (a more recent version is available)
...
To show all packages with “`zip`” in the name:
$ nix-env -qa '.*zip.*'
bzip2-1.0.6
gzip-1.6
zip-3.0
…
To show all packages with “`firefox`” or “`chromium`” in the name:
$ nix-env -qa '.*(firefox|chromium).*'
chromium-37.0.2062.94
chromium-beta-38.0.2125.24
firefox-32.0.3
firefox-with-plugins-13.0.1
…
To show all packages in the latest revision of the Nixpkgs repository:
$ nix-env -f https://github.com/NixOS/nixpkgs/archive/master.tar.gz -qa
# Operation `--switch-profile`
## Synopsis
nix-env
\--switch-profile
\-S
path
## Description
This operation makes path the current profile for the user. That is, the
symlink `~/.nix-profile` is made to point to path.
## Examples
$ nix-env -S ~/my-profile
# Operation `--list-generations`
## Synopsis
nix-env
\--list-generations
## Description
This operation print a list of all the currently existing generations
for the active profile. These may be switched to using the
`--switch-generation` operation. It also prints the creation date of the
generation, and indicates the current generation.
## Examples
$ nix-env --list-generations
95 2004-02-06 11:48:24
96 2004-02-06 11:49:01
97 2004-02-06 16:22:45
98 2004-02-06 16:24:33 (current)
# Operation `--delete-generations`
## Synopsis
nix-env
\--delete-generations
generations
## Description
This operation deletes the specified generations of the current profile.
The generations can be a list of generation numbers, the special value
`old` to delete all non-current generations, a value such as `30d` to
delete all generations older than the specified number of days (except
for the generation that was active at that point in time), or a value
such as `+5` to keep the last `5` generations ignoring any newer than
current, e.g., if `30` is the current generation `+5` will delete
generation `25` and all older generations. Periodically deleting old
generations is important to make garbage collection effective.
## Examples
$ nix-env --delete-generations 3 4 8
$ nix-env --delete-generations +5
$ nix-env --delete-generations 30d
$ nix-env -p other_profile --delete-generations old
# Operation `--switch-generation`
## Synopsis
nix-env
\--switch-generation
\-G
generation
## Description
This operation makes generation number generation the current generation
of the active profile. That is, if the `profile` is the path to the
active profile, then the symlink `profile` is made to point to
`profile-generation-link`, which is in turn a symlink to the actual user
environment in the Nix store.
Switching will fail if the specified generation does not exist.
## Examples
$ nix-env -G 42
switching from generation 50 to 42
# Operation `--rollback`
## Synopsis
nix-env
\--rollback
## Description
This operation switches to the “previous” generation of the active
profile, that is, the highest numbered generation lower than the current
generation, if it exists. It is just a convenience wrapper around
`--list-generations` and `--switch-generation`.
## Examples
$ nix-env --rollback
switching from generation 92 to 91
$ nix-env --rollback
error: no generation older than the current (91) exists
# Environment variables
- `NIX_PROFILE`
Location of the Nix profile. Defaults to the target of the symlink
`~/.nix-profile`, if it exists, or `/nix/var/nix/profiles/default`
otherwise.

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nix-hash
1
Nix
nix-hash
compute the cryptographic hash of a path
nix-hash
\--flat
\--base32
\--truncate
\--type
hashAlgo
path
nix-hash
\--to-base16
hash
nix-hash
\--to-base32
hash
# Description
The command `nix-hash` computes the cryptographic hash of the contents
of each path and prints it on standard output. By default, it computes
an MD5 hash, but other hash algorithms are available as well. The hash
is printed in hexadecimal. To generate the same hash as
`nix-prefetch-url` you have to specify multiple arguments, see below for
an example.
The hash is computed over a *serialisation* of each path: a dump of the
file system tree rooted at the path. This allows directories and
symlinks to be hashed as well as regular files. The dump is in the *NAR
format* produced by [`nix-store` `--dump`](#refsec-nix-store-dump).
Thus, `nix-hash
path` yields the same cryptographic hash as `nix-store --dump
path | md5sum`.
# Options
- `--flat`
Print the cryptographic hash of the contents of each regular file
path. That is, do not compute the hash over the dump of path. The
result is identical to that produced by the GNU commands `md5sum`
and `sha1sum`.
- `--base32`
Print the hash in a base-32 representation rather than hexadecimal.
This base-32 representation is more compact and can be used in Nix
expressions (such as in calls to `fetchurl`).
- `--truncate`
Truncate hashes longer than 160 bits (such as SHA-256) to 160 bits.
- `--type` hashAlgo
Use the specified cryptographic hash algorithm, which can be one of
`md5`, `sha1`, and `sha256`.
- `--to-base16`
Don’t hash anything, but convert the base-32 hash representation
hash to hexadecimal.
- `--to-base32`
Don’t hash anything, but convert the hexadecimal hash representation
hash to base-32.
# Examples
Computing the same hash as `nix-prefetch-url`:
$ nix-prefetch-url file://<(echo test)
1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
$ nix-hash --type sha256 --flat --base32 <(echo test)
1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
Computing hashes:
$ mkdir test
$ echo "hello" > test/world
$ nix-hash test/ (MD5 hash; default)
8179d3caeff1869b5ba1744e5a245c04
$ nix-store --dump test/ | md5sum (for comparison)
8179d3caeff1869b5ba1744e5a245c04 -
$ nix-hash --type sha1 test/
e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
$ nix-hash --type sha1 --base32 test/
nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
$ nix-hash --type sha256 --flat test/
error: reading file `test/': Is a directory
$ nix-hash --type sha256 --flat test/world
5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
Converting between hexadecimal and base-32:
$ nix-hash --type sha1 --to-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
$ nix-hash --type sha1 --to-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6

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nix-instantiate
1
Nix
nix-instantiate
instantiate store derivations from Nix expressions
nix-instantiate
\--parse
\--eval
\--strict
\--json
\--xml
\--read-write-mode
\--arg
name
value
\--attr
\-A
attrPath
\--add-root
path
\--indirect
\--expr
\-E
files
nix-instantiate
\--find-file
files
# Description
The command `nix-instantiate` generates [store
derivations](#gloss-derivation) from (high-level) Nix expressions. It
evaluates the Nix expressions in each of files (which defaults to
./default.nix). Each top-level expression should evaluate to a
derivation, a list of derivations, or a set of derivations. The paths of
the resulting store derivations are printed on standard output.
If files is the character `-`, then a Nix expression will be read from
standard input.
See also [???](#sec-common-options) for a list of common options.
# Options
- `--add-root` path; `--indirect`
See the [corresponding options](#opt-add-root) in `nix-store`.
- `--parse`
Just parse the input files, and print their abstract syntax trees on
standard output in ATerm format.
- `--eval`
Just parse and evaluate the input files, and print the resulting
values on standard output. No instantiation of store derivations
takes place.
- `--find-file`
Look up the given files in Nix’s search path (as specified by the
NIX\_PATH\</literal\> environment variable). If found, print the
corresponding absolute paths on standard output. For instance, if
`NIX_PATH` is `nixpkgs=/home/alice/nixpkgs`, then `nix-instantiate
--find-file nixpkgs/default.nix` will print
`/home/alice/nixpkgs/default.nix`.
- `--strict`
When used with `--eval`, recursively evaluate list elements and
attributes. Normally, such sub-expressions are left unevaluated
(since the Nix expression language is lazy).
> **Warning**
>
> This option can cause non-termination, because lazy data
> structures can be infinitely large.
- `--json`
When used with `--eval`, print the resulting value as an JSON
representation of the abstract syntax tree rather than as an ATerm.
- `--xml`
When used with `--eval`, print the resulting value as an XML
representation of the abstract syntax tree rather than as an ATerm.
The schema is the same as that used by the [`toXML`
built-in](#builtin-toXML).
- `--read-write-mode`
When used with `--eval`, perform evaluation in read/write mode so
nix language features that require it will still work (at the cost
of needing to do instantiation of every evaluated derivation). If
this option is not enabled, there may be uninstantiated store paths
in the final output.
<!-- end list -->
# Examples
Instantiating store derivations from a Nix expression, and building them
using `nix-store`:
$ nix-instantiate test.nix (instantiate)
/nix/store/cigxbmvy6dzix98dxxh9b6shg7ar5bvs-perl-BerkeleyDB-0.26.drv
$ nix-store -r $(nix-instantiate test.nix) (build)
...
/nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26 (output path)
$ ls -l /nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26
dr-xr-xr-x 2 eelco users 4096 1970-01-01 01:00 lib
...
You can also give a Nix expression on the command line:
$ nix-instantiate -E 'with import <nixpkgs> { }; hello'
/nix/store/j8s4zyv75a724q38cb0r87rlczaiag4y-hello-2.8.drv
This is equivalent to:
$ nix-instantiate '<nixpkgs>' -A hello
Parsing and evaluating Nix expressions:
$ nix-instantiate --parse -E '1 + 2'
1 + 2
$ nix-instantiate --eval -E '1 + 2'
3
$ nix-instantiate --eval --xml -E '1 + 2'
<?xml version='1.0' encoding='utf-8'?>
<expr>
<int value="3" />
</expr>
The difference between non-strict and strict evaluation:
$ nix-instantiate --eval --xml -E 'rec { x = "foo"; y = x; }'
...
<attr name="x">
<string value="foo" />
</attr>
<attr name="y">
<unevaluated />
</attr>
...
Note that `y` is left unevaluated (the XML representation doesn’t
attempt to show non-normal forms).
$ nix-instantiate --eval --xml --strict -E 'rec { x = "foo"; y = x; }'
...
<attr name="x">
<string value="foo" />
</attr>
<attr name="y">
<string value="foo" />
</attr>
...
# Environment variables

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nix-prefetch-url
1
Nix
nix-prefetch-url
copy a file from a URL into the store and print its hash
nix-prefetch-url
\--version
\--type
hashAlgo
\--print-path
\--unpack
\--name
name
url
hash
# Description
The command `nix-prefetch-url` downloads the file referenced by the URL
url, prints its cryptographic hash, and copies it into the Nix store.
The file name in the store is `hash-baseName`, where baseName is
everything following the final slash in url.
This command is just a convenience for Nix expression writers. Often a
Nix expression fetches some source distribution from the network using
the `fetchurl` expression contained in Nixpkgs. However, `fetchurl`
requires a cryptographic hash. If you don't know the hash, you would
have to download the file first, and then `fetchurl` would download it
again when you build your Nix expression. Since `fetchurl` uses the same
name for the downloaded file as `nix-prefetch-url`, the redundant
download can be avoided.
If hash is specified, then a download is not performed if the Nix store
already contains a file with the same hash and base name. Otherwise, the
file is downloaded, and an error is signaled if the actual hash of the
file does not match the specified hash.
This command prints the hash on standard output. Additionally, if the
option `--print-path` is used, the path of the downloaded file in the
Nix store is also printed.
# Options
- `--type` hashAlgo
Use the specified cryptographic hash algorithm, which can be one of
`md5`, `sha1`, and `sha256`.
- `--print-path`
Print the store path of the downloaded file on standard output.
- `--unpack`
Unpack the archive (which must be a tarball or zip file) and add the
result to the Nix store. The resulting hash can be used with
functions such as Nixpkgs’s `fetchzip` or `fetchFromGitHub`.
- `--name` name
Override the name of the file in the Nix store. By default, this is
`hash-basename`, where basename is the last component of url.
Overriding the name is necessary when basename contains characters
that are not allowed in Nix store paths.
# Examples
$ nix-prefetch-url ftp://ftp.gnu.org/pub/gnu/hello/hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
$ nix-prefetch-url --print-path mirror://gnu/hello/hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz
$ nix-prefetch-url --unpack --print-path https://github.com/NixOS/patchelf/archive/0.8.tar.gz
079agjlv0hrv7fxnx9ngipx14gyncbkllxrp9cccnh3a50fxcmy7
/nix/store/19zrmhm3m40xxaw81c8cqm6aljgrnwj2-0.8.tar.gz

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nix-shell
1
Nix
nix-shell
start an interactive shell based on a Nix expression
nix-shell
\--arg
name
value
\--argstr
name
value
\--attr
\-A
attrPath
\--command
cmd
\--run
cmd
\--exclude
regexp
\--pure
\--keep
name
\--packages
\-p
packages
expressions
path
# Description
The command `nix-shell` will build the dependencies of the specified
derivation, but not the derivation itself. It will then start an
interactive shell in which all environment variables defined by the
derivation path have been set to their corresponding values, and the
script `$stdenv/setup` has been sourced. This is useful for reproducing
the environment of a derivation for development.
If path is not given, `nix-shell` defaults to `shell.nix` if it exists,
and `default.nix` otherwise.
If path starts with `http://` or `https://`, it is interpreted as the
URL of a tarball that will be downloaded and unpacked to a temporary
location. The tarball must include a single top-level directory
containing at least a file named `default.nix`.
If the derivation defines the variable `shellHook`, it will be evaluated
after `$stdenv/setup` has been sourced. Since this hook is not executed
by regular Nix builds, it allows you to perform initialisation specific
to `nix-shell`. For example, the derivation attribute
shellHook =
''
echo "Hello shell"
'';
will cause `nix-shell` to print `Hello shell`.
# Options
All options not listed here are passed to `nix-store
--realise`, except for `--arg` and `--attr` / `-A` which are passed to
`nix-instantiate`. See also [???](#sec-common-options).
- `--command` cmd
In the environment of the derivation, run the shell command cmd.
This command is executed in an interactive shell. (Use `--run` to
use a non-interactive shell instead.) However, a call to `exit` is
implicitly added to the command, so the shell will exit after
running the command. To prevent this, add `return` at the end; e.g.
`--command
"echo Hello; return"` will print `Hello` and then drop you into the
interactive shell. This can be useful for doing any additional
initialisation.
- `--run` cmd
Like `--command`, but executes the command in a non-interactive
shell. This means (among other things) that if you hit Ctrl-C while
the command is running, the shell exits.
- `--exclude` regexp
Do not build any dependencies whose store path matches the regular
expression regexp. This option may be specified multiple times.
- `--pure`
If this flag is specified, the environment is almost entirely
cleared before the interactive shell is started, so you get an
environment that more closely corresponds to the “real” Nix build. A
few variables, in particular `HOME`, `USER` and `DISPLAY`, are
retained. Note that `~/.bashrc` and (depending on your Bash
installation) `/etc/bashrc` are still sourced, so any variables set
there will affect the interactive shell.
- `--packages` / `-p` packages…
Set up an environment in which the specified packages are present.
The command line arguments are interpreted as attribute names inside
the Nix Packages collection. Thus, `nix-shell -p libjpeg openjdk`
will start a shell in which the packages denoted by the attribute
names `libjpeg` and `openjdk` are present.
- `-i` interpreter
The chained script interpreter to be invoked by `nix-shell`. Only
applicable in `#!`-scripts (described
[below](#ssec-nix-shell-shebang)).
- `--keep` name
When a `--pure` shell is started, keep the listed environment
variables.
The following common options are supported:
# Environment variables
- `NIX_BUILD_SHELL`
Shell used to start the interactive environment. Defaults to the
`bash` found in `PATH`.
# Examples
To build the dependencies of the package Pan, and start an interactive
shell in which to build it:
$ nix-shell '<nixpkgs>' -A pan
[nix-shell]$ unpackPhase
[nix-shell]$ cd pan-*
[nix-shell]$ configurePhase
[nix-shell]$ buildPhase
[nix-shell]$ ./pan/gui/pan
To clear the environment first, and do some additional automatic
initialisation of the interactive shell:
$ nix-shell '<nixpkgs>' -A pan --pure \
--command 'export NIX_DEBUG=1; export NIX_CORES=8; return'
Nix expressions can also be given on the command line using the `-E` and
`-p` flags. For instance, the following starts a shell containing the
packages `sqlite` and `libX11`:
$ nix-shell -E 'with import <nixpkgs> { }; runCommand "dummy" { buildInputs = [ sqlite xorg.libX11 ]; } ""'
A shorter way to do the same is:
$ nix-shell -p sqlite xorg.libX11
[nix-shell]$ echo $NIX_LDFLAGS
… -L/nix/store/j1zg5v…-sqlite-3.8.0.2/lib -L/nix/store/0gmcz9…-libX11-1.6.1/lib …
Note that `-p` accepts multiple full nix expressions that are valid in
the `buildInputs = [ ... ]` shown above, not only package names. So the
following is also legal:
$ nix-shell -p sqlite 'git.override { withManual = false; }'
The `-p` flag looks up Nixpkgs in the Nix search path. You can override
it by passing `-I` or setting `NIX_PATH`. For example, the following
gives you a shell containing the Pan package from a specific revision of
Nixpkgs:
$ nix-shell -p pan -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz
[nix-shell:~]$ pan --version
Pan 0.139
# Use as a `#!`-interpreter
You can use `nix-shell` as a script interpreter to allow scripts written
in arbitrary languages to obtain their own dependencies via Nix. This is
done by starting the script with the following lines:
#! /usr/bin/env nix-shell
#! nix-shell -i real-interpreter -p packages
where real-interpreter is the “real” script interpreter that will be
invoked by `nix-shell` after it has obtained the dependencies and
initialised the environment, and packages are the attribute names of the
dependencies in Nixpkgs.
The lines starting with `#! nix-shell` specify `nix-shell` options (see
above). Note that you cannot write `#! /usr/bin/env nix-shell -i ...`
because many operating systems only allow one argument in `#!` lines.
For example, here is a Python script that depends on Python and the
`prettytable` package:
#! /usr/bin/env nix-shell
#! nix-shell -i python -p python pythonPackages.prettytable
import prettytable
# Print a simple table.
t = prettytable.PrettyTable(["N", "N^2"])
for n in range(1, 10): t.add_row([n, n * n])
print t
Similarly, the following is a Perl script that specifies that it
requires Perl and the `HTML::TokeParser::Simple` and `LWP` packages:
#! /usr/bin/env nix-shell
#! nix-shell -i perl -p perl perlPackages.HTMLTokeParserSimple perlPackages.LWP
use HTML::TokeParser::Simple;
# Fetch nixos.org and print all hrefs.
my $p = HTML::TokeParser::Simple->new(url => 'http://nixos.org/');
while (my $token = $p->get_tag("a")) {
my $href = $token->get_attr("href");
print "$href\n" if $href;
}
Sometimes you need to pass a simple Nix expression to customize a
package like Terraform:
#! /usr/bin/env nix-shell
#! nix-shell -i bash -p "terraform.withPlugins (plugins: [ plugins.openstack ])"
terraform apply
> **Note**
>
> You must use double quotes (`"`) when passing a simple Nix expression
> in a nix-shell shebang.
Finally, using the merging of multiple nix-shell shebangs the following
Haskell script uses a specific branch of Nixpkgs/NixOS (the 18.03 stable
branch):
#! /usr/bin/env nix-shell
#! nix-shell -i runghc -p "haskellPackages.ghcWithPackages (ps: [ps.HTTP ps.tagsoup])"
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-18.03.tar.gz
import Network.HTTP
import Text.HTML.TagSoup
-- Fetch nixos.org and print all hrefs.
main = do
resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/")
body <- getResponseBody resp
let tags = filter (isTagOpenName "a") $ parseTags body
let tags' = map (fromAttrib "href") tags
mapM_ putStrLn $ filter (/= "") tags'
If you want to be even more precise, you can specify a specific revision
of Nixpkgs:
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/0672315759b3e15e2121365f067c1c8c56bb4722.tar.gz
The examples above all used `-p` to get dependencies from Nixpkgs. You
can also use a Nix expression to build your own dependencies. For
example, the Python example could have been written as:
#! /usr/bin/env nix-shell
#! nix-shell deps.nix -i python
where the file `deps.nix` in the same directory as the `#!`-script
contains:
with import <nixpkgs> {};
runCommand "dummy" { buildInputs = [ python pythonPackages.prettytable ]; } ""
# Environment variables

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@ -0,0 +1,954 @@
nix-store
1
Nix
nix-store
manipulate or query the Nix store
nix-store
\--add-root
path
\--indirect
operation
options
arguments
# Description
The command `nix-store` performs primitive operations on the Nix store.
You generally do not need to run this command manually.
`nix-store` takes exactly one *operation* flag which indicates the
subcommand to be performed. These are documented below.
# Common options
This section lists the options that are common to all operations. These
options are allowed for every subcommand, though they may not always
have an effect. See also [???](#sec-common-options) for a list of common
options.
- `--add-root` path
Causes the result of a realisation (`--realise` and
`--force-realise`) to be registered as a root of the garbage
collector(see [???](#ssec-gc-roots)). The root is stored in path,
which must be inside a directory that is scanned for roots by the
garbage collector (i.e., typically in a subdirectory of
`/nix/var/nix/gcroots/`) *unless* the `--indirect` flag is used.
If there are multiple results, then multiple symlinks will be
created by sequentially numbering symlinks beyond the first one
(e.g., `foo`, `foo-2`, `foo-3`, and so on).
- `--indirect`
In conjunction with `--add-root`, this option allows roots to be
stored *outside* of the GC roots directory. This is useful for
commands such as `nix-build` that place a symlink to the build
result in the current directory; such a build result should not be
garbage-collected unless the symlink is removed.
The `--indirect` flag causes a uniquely named symlink to path to be
stored in `/nix/var/nix/gcroots/auto/`. For instance,
$ nix-store --add-root /home/eelco/bla/result --indirect -r ...
$ ls -l /nix/var/nix/gcroots/auto
lrwxrwxrwx 1 ... 2005-03-13 21:10 dn54lcypm8f8... -> /home/eelco/bla/result
$ ls -l /home/eelco/bla/result
lrwxrwxrwx 1 ... 2005-03-13 21:10 /home/eelco/bla/result -> /nix/store/1r11343n6qd4...-f-spot-0.0.10
Thus, when `/home/eelco/bla/result` is removed, the GC root in the
`auto` directory becomes a dangling symlink and will be ignored by
the collector.
> **Warning**
>
> Note that it is not possible to move or rename indirect GC roots,
> since the symlink in the `auto` directory will still point to the
> old location.
<!-- end list -->
# Operation `--realise`
## Synopsis
nix-store
\--realise
\-r
paths
\--dry-run
## Description
The operation `--realise` essentially “builds” the specified store
paths. Realisation is a somewhat overloaded term:
- If the store path is a *derivation*, realisation ensures that the
output paths of the derivation are [valid](#gloss-validity) (i.e.,
the output path and its closure exist in the file system). This can
be done in several ways. First, it is possible that the outputs are
already valid, in which case we are done immediately. Otherwise,
there may be [substitutes](#gloss-substitute) that produce the
outputs (e.g., by downloading them). Finally, the outputs can be
produced by performing the build action described by the derivation.
- If the store path is not a derivation, realisation ensures that the
specified path is valid (i.e., it and its closure exist in the file
system). If the path is already valid, we are done immediately.
Otherwise, the path and any missing paths in its closure may be
produced through substitutes. If there are no (successful)
subsitutes, realisation fails.
The output path of each derivation is printed on standard output. (For
non-derivations argument, the argument itself is printed.)
The following flags are available:
- `--dry-run`
Print on standard error a description of what packages would be
built or downloaded, without actually performing the operation.
- `--ignore-unknown`
If a non-derivation path does not have a substitute, then silently
ignore it.
- `--check`
This option allows you to check whether a derivation is
deterministic. It rebuilds the specified derivation and checks
whether the result is bitwise-identical with the existing outputs,
printing an error if that’s not the case. The outputs of the
specified derivation must already exist. When used with `-K`, if an
output path is not identical to the corresponding output from the
previous build, the new output path is left in
`/nix/store/name.check.`
See also the `build-repeat` configuration option, which repeats a
derivation a number of times and prevents its outputs from being
registered as “valid” in the Nix store unless they are identical.
Special exit codes:
- `100`
Generic build failure, the builder process returned with a non-zero
exit code.
- `101`
Build timeout, the build was aborted because it did not complete
within the specified [`timeout`](#conf-timeout).
- `102`
Hash mismatch, the build output was rejected because it does not
match the specified [`outputHash`](#fixed-output-drvs).
- `104`
Not deterministic, the build succeeded in check mode but the
resulting output is not binary reproducable.
With the `--keep-going` flag it's possible for multiple failures to
occur, in this case the 1xx status codes are or combined using binary
or.
1100100
^^^^
|||`- timeout
||`-- output hash mismatch
|`--- build failure
`---- not deterministic
## Examples
This operation is typically used to build store derivations produced by
[`nix-instantiate`](#sec-nix-instantiate):
$ nix-store -r $(nix-instantiate ./test.nix)
/nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1
This is essentially what [`nix-build`](#sec-nix-build) does.
To test whether a previously-built derivation is deterministic:
$ nix-build '<nixpkgs>' -A hello --check -K
# Operation `--serve`
## Synopsis
nix-store
\--serve
\--write
## Description
The operation `--serve` provides access to the Nix store over stdin and
stdout, and is intended to be used as a means of providing Nix store
access to a restricted ssh user.
The following flags are available:
- `--write`
Allow the connected client to request the realization of
derivations. In effect, this can be used to make the host act as a
remote builder.
## Examples
To turn a host into a build server, the `authorized_keys` file can be
used to provide build access to a given SSH public key:
$ cat <<EOF >>/root/.ssh/authorized_keys
command="nice -n20 nix-store --serve --write" ssh-rsa AAAAB3NzaC1yc2EAAAA...
EOF
# Operation `--gc`
## Synopsis
nix-store
\--gc
\--print-roots
\--print-live
\--print-dead
\--max-freed
bytes
## Description
Without additional flags, the operation `--gc` performs a garbage
collection on the Nix store. That is, all paths in the Nix store not
reachable via file system references from a set of “roots”, are deleted.
The following suboperations may be specified:
- `--print-roots`
This operation prints on standard output the set of roots used by
the garbage collector. What constitutes a root is described in
[???](#ssec-gc-roots).
- `--print-live`
This operation prints on standard output the set of “live” store
paths, which are all the store paths reachable from the roots. Live
paths should never be deleted, since that would break consistency —
it would become possible that applications are installed that
reference things that are no longer present in the store.
- `--print-dead`
This operation prints out on standard output the set of “dead” store
paths, which is just the opposite of the set of live paths: any path
in the store that is not live (with respect to the roots) is dead.
By default, all unreachable paths are deleted. The following options
control what gets deleted and in what order:
- `--max-freed` bytes
Keep deleting paths until at least bytes bytes have been deleted,
then stop. The argument bytes can be followed by the multiplicative
suffix `K`, `M`, `G` or `T`, denoting KiB, MiB, GiB or TiB units.
The behaviour of the collector is also influenced by the
[`keep-outputs`](#conf-keep-outputs) and
[`keep-derivations`](#conf-keep-derivations) variables in the Nix
configuration file.
By default, the collector prints the total number of freed bytes when it
finishes (or when it is interrupted). With `--print-dead`, it prints the
number of bytes that would be freed.
## Examples
To delete all unreachable paths, just do:
$ nix-store --gc
deleting `/nix/store/kq82idx6g0nyzsp2s14gfsc38npai7lf-cairo-1.0.4.tar.gz.drv'
...
8825586 bytes freed (8.42 MiB)
To delete at least 100 MiBs of unreachable paths:
$ nix-store --gc --max-freed $((100 * 1024 * 1024))
# Operation `--delete`
## Synopsis
nix-store
\--delete
\--ignore-liveness
paths
## Description
The operation `--delete` deletes the store paths paths from the Nix
store, but only if it is safe to do so; that is, when the path is not
reachable from a root of the garbage collector. This means that you can
only delete paths that would also be deleted by `nix-store --gc`. Thus,
`--delete` is a more targeted version of `--gc`.
With the option `--ignore-liveness`, reachability from the roots is
ignored. However, the path still won’t be deleted if there are other
paths in the store that refer to it (i.e., depend on it).
## Example
$ nix-store --delete /nix/store/zq0h41l75vlb4z45kzgjjmsjxvcv1qk7-mesa-6.4
0 bytes freed (0.00 MiB)
error: cannot delete path `/nix/store/zq0h41l75vlb4z45kzgjjmsjxvcv1qk7-mesa-6.4' since it is still alive
# Operation `--query`
## Synopsis
nix-store
\--query
\-q
\--outputs
\--requisites
\-R
\--references
\--referrers
\--referrers-closure
\--deriver
\-d
\--graph
\--tree
\--binding
name
\-b
name
\--hash
\--size
\--roots
\--use-output
\-u
\--force-realise
\-f
paths
## Description
The operation `--query` displays various bits of information about the
store paths . The queries are described below. At most one query can be
specified. The default query is `--outputs`.
The paths paths may also be symlinks from outside of the Nix store, to
the Nix store. In that case, the query is applied to the target of the
symlink.
## Common query options
- `--use-output`; `-u`
For each argument to the query that is a store derivation, apply the
query to the output path of the derivation instead.
- `--force-realise`; `-f`
Realise each argument to the query first (see [`nix-store
--realise`](#rsec-nix-store-realise)).
## Queries
- `--outputs`
Prints out the [output paths](#gloss-output-path) of the store
derivations paths. These are the paths that will be produced when
the derivation is built.
- `--requisites`; `-R`
Prints out the [closure](#gloss-closure) of the store path paths.
This query has one option:
- `--include-outputs`
Also include the output path of store derivations, and their
closures.
This query can be used to implement various kinds of deployment. A
*source deployment* is obtained by distributing the closure of a
store derivation. A *binary deployment* is obtained by distributing
the closure of an output path. A *cache deployment* (combined
source/binary deployment, including binaries of build-time-only
dependencies) is obtained by distributing the closure of a store
derivation and specifying the option `--include-outputs`.
- `--references`
Prints the set of [references](#gloss-reference) of the store paths
paths, that is, their immediate dependencies. (For *all*
dependencies, use `--requisites`.)
- `--referrers`
Prints the set of *referrers* of the store paths paths, that is, the
store paths currently existing in the Nix store that refer to one of
paths. Note that contrary to the references, the set of referrers is
not constant; it can change as store paths are added or removed.
- `--referrers-closure`
Prints the closure of the set of store paths paths under the
referrers relation; that is, all store paths that directly or
indirectly refer to one of paths. These are all the path currently
in the Nix store that are dependent on paths.
- `--deriver`; `-d`
Prints the [deriver](#gloss-deriver) of the store paths paths. If
the path has no deriver (e.g., if it is a source file), or if the
deriver is not known (e.g., in the case of a binary-only
deployment), the string `unknown-deriver` is printed.
- `--graph`
Prints the references graph of the store paths paths in the format
of the `dot` tool of AT\&T's [Graphviz
package](http://www.graphviz.org/). This can be used to visualise
dependency graphs. To obtain a build-time dependency graph, apply
this to a store derivation. To obtain a runtime dependency graph,
apply it to an output path.
- `--tree`
Prints the references graph of the store paths paths as a nested
ASCII tree. References are ordered by descending closure size; this
tends to flatten the tree, making it more readable. The query only
recurses into a store path when it is first encountered; this
prevents a blowup of the tree representation of the graph.
- `--graphml`
Prints the references graph of the store paths paths in the
[GraphML](http://graphml.graphdrawing.org/) file format. This can be
used to visualise dependency graphs. To obtain a build-time
dependency graph, apply this to a store derivation. To obtain a
runtime dependency graph, apply it to an output path.
- `--binding` name; `-b` name
Prints the value of the attribute name (i.e., environment variable)
of the store derivations paths. It is an error for a derivation to
not have the specified attribute.
- `--hash`
Prints the SHA-256 hash of the contents of the store paths paths
(that is, the hash of the output of `nix-store --dump` on the given
paths). Since the hash is stored in the Nix database, this is a fast
operation.
- `--size`
Prints the size in bytes of the contents of the store paths paths —
to be precise, the size of the output of `nix-store --dump` on the
given paths. Note that the actual disk space required by the store
paths may be higher, especially on filesystems with large cluster
sizes.
- `--roots`
Prints the garbage collector roots that point, directly or
indirectly, at the store paths paths.
## Examples
Print the closure (runtime dependencies) of the `svn` program in the
current user environment:
$ nix-store -qR $(which svn)
/nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4
/nix/store/9lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4
...
Print the build-time dependencies of `svn`:
$ nix-store -qR $(nix-store -qd $(which svn))
/nix/store/02iizgn86m42q905rddvg4ja975bk2i4-grep-2.5.1.tar.bz2.drv
/nix/store/07a2bzxmzwz5hp58nf03pahrv2ygwgs3-gcc-wrapper.sh
/nix/store/0ma7c9wsbaxahwwl04gbw3fcd806ski4-glibc-2.3.4.drv
... lots of other paths ...
The difference with the previous example is that we ask the closure of
the derivation (`-qd`), not the closure of the output path that contains
`svn`.
Show the build-time dependencies as a tree:
$ nix-store -q --tree $(nix-store -qd $(which svn))
/nix/store/7i5082kfb6yjbqdbiwdhhza0am2xvh6c-subversion-1.1.4.drv
+---/nix/store/d8afh10z72n8l1cr5w42366abiblgn54-builder.sh
+---/nix/store/fmzxmpjx2lh849ph0l36snfj9zdibw67-bash-3.0.drv
| +---/nix/store/570hmhmx3v57605cqg9yfvvyh0nnb8k8-bash
| +---/nix/store/p3srsbd8dx44v2pg6nbnszab5mcwx03v-builder.sh
...
Show all paths that depend on the same OpenSSL library as `svn`:
$ nix-store -q --referrers $(nix-store -q --binding openssl $(nix-store -qd $(which svn)))
/nix/store/23ny9l9wixx21632y2wi4p585qhva1q8-sylpheed-1.0.0
/nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4
/nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3
/nix/store/l51240xqsgg8a7yrbqdx1rfzyv6l26fx-lynx-2.8.5
Show all paths that directly or indirectly depend on the Glibc (C
library) used by `svn`:
$ nix-store -q --referrers-closure $(ldd $(which svn) | grep /libc.so | awk '{print $3}')
/nix/store/034a6h4vpz9kds5r6kzb9lhh81mscw43-libgnomeprintui-2.8.2
/nix/store/15l3yi0d45prm7a82pcrknxdh6nzmxza-gawk-3.1.4
...
Note that `ldd` is a command that prints out the dynamic libraries used
by an ELF executable.
Make a picture of the runtime dependency graph of the current user
environment:
$ nix-store -q --graph ~/.nix-profile | dot -Tps > graph.ps
$ gv graph.ps
Show every garbage collector root that points to a store path that
depends on `svn`:
$ nix-store -q --roots $(which svn)
/nix/var/nix/profiles/default-81-link
/nix/var/nix/profiles/default-82-link
/nix/var/nix/profiles/per-user/eelco/profile-97-link
# Operation `--add`
## Synopsis
nix-store
\--add
paths
## Description
The operation `--add` adds the specified paths to the Nix store. It
prints the resulting paths in the Nix store on standard output.
## Example
$ nix-store --add ./foo.c
/nix/store/m7lrha58ph6rcnv109yzx1nk1cj7k7zf-foo.c
# Operation `--add-fixed`
## Synopsis
nix-store
\--recursive
\--add-fixed
algorithm
paths
## Description
The operation `--add-fixed` adds the specified paths to the Nix store.
Unlike `--add` paths are registered using the specified hashing
algorithm, resulting in the same output path as a fixed-output
derivation. This can be used for sources that are not available from a
public url or broke since the download expression was written.
This operation has the following options:
- `--recursive`
Use recursive instead of flat hashing mode, used when adding
directories to the store.
## Example
$ nix-store --add-fixed sha256 ./hello-2.10.tar.gz
/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz
# Operation `--verify`
## Synopsis
nix-store
\--verify
\--check-contents
\--repair
## Description
The operation `--verify` verifies the internal consistency of the Nix
database, and the consistency between the Nix database and the Nix
store. Any inconsistencies encountered are automatically repaired.
Inconsistencies are generally the result of the Nix store or database
being modified by non-Nix tools, or of bugs in Nix itself.
This operation has the following options:
- `--check-contents`
Checks that the contents of every valid store path has not been
altered by computing a SHA-256 hash of the contents and comparing it
with the hash stored in the Nix database at build time. Paths that
have been modified are printed out. For large stores,
`--check-contents` is obviously quite slow.
- `--repair`
If any valid path is missing from the store, or (if
`--check-contents` is given) the contents of a valid path has been
modified, then try to repair the path by redownloading it. See
`nix-store --repair-path` for details.
# Operation `--verify-path`
## Synopsis
nix-store
\--verify-path
paths
## Description
The operation `--verify-path` compares the contents of the given store
paths to their cryptographic hashes stored in Nix’s database. For every
changed path, it prints a warning message. The exit status is 0 if no
path has changed, and 1 otherwise.
## Example
To verify the integrity of the `svn` command and all its dependencies:
$ nix-store --verify-path $(nix-store -qR $(which svn))
# Operation `--repair-path`
## Synopsis
nix-store
\--repair-path
paths
## Description
The operation `--repair-path` attempts to “repair” the specified paths
by redownloading them using the available substituters. If no
substitutes are available, then repair is not possible.
> **Warning**
>
> During repair, there is a very small time window during which the old
> path (if it exists) is moved out of the way and replaced with the new
> path. If repair is interrupted in between, then the system may be left
> in a broken state (e.g., if the path contains a critical system
> component like the GNU C Library).
## Example
$ nix-store --verify-path /nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13
path `/nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13' was modified!
expected hash `2db57715ae90b7e31ff1f2ecb8c12ec1cc43da920efcbe3b22763f36a1861588',
got `481c5aa5483ebc97c20457bb8bca24deea56550d3985cda0027f67fe54b808e4'
$ nix-store --repair-path /nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13
fetching path `/nix/store/d7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13'...
…
# Operation `--dump`
## Synopsis
nix-store
\--dump
path
## Description
The operation `--dump` produces a NAR (Nix ARchive) file containing the
contents of the file system tree rooted at path. The archive is written
to standard output.
A NAR archive is like a TAR or Zip archive, but it contains only the
information that Nix considers important. For instance, timestamps are
elided because all files in the Nix store have their timestamp set to 0
anyway. Likewise, all permissions are left out except for the execute
bit, because all files in the Nix store have 444 or 555 permission.
Also, a NAR archive is *canonical*, meaning that “equal” paths always
produce the same NAR archive. For instance, directory entries are always
sorted so that the actual on-disk order doesn’t influence the result.
This means that the cryptographic hash of a NAR dump of a path is usable
as a fingerprint of the contents of the path. Indeed, the hashes of
store paths stored in Nix’s database (see [`nix-store -q
--hash`](#refsec-nix-store-query)) are SHA-256 hashes of the NAR dump of
each store path.
NAR archives support filenames of unlimited length and 64-bit file
sizes. They can contain regular files, directories, and symbolic links,
but not other types of files (such as device nodes).
A Nix archive can be unpacked using `nix-store
--restore`.
# Operation `--restore`
## Synopsis
nix-store
\--restore
path
## Description
The operation `--restore` unpacks a NAR archive to path, which must not
already exist. The archive is read from standard input.
# Operation `--export`
## Synopsis
nix-store
\--export
paths
## Description
The operation `--export` writes a serialisation of the specified store
paths to standard output in a format that can be imported into another
Nix store with `nix-store --import`. This is like `nix-store
--dump`, except that the NAR archive produced by that command doesn’t
contain the necessary meta-information to allow it to be imported into
another Nix store (namely, the set of references of the path).
This command does not produce a *closure* of the specified paths, so if
a store path references other store paths that are missing in the target
Nix store, the import will fail. To copy a whole closure, do something
like:
$ nix-store --export $(nix-store -qR paths) > out
To import the whole closure again, run:
$ nix-store --import < out
# Operation `--import`
## Synopsis
nix-store
\--import
## Description
The operation `--import` reads a serialisation of a set of store paths
produced by `nix-store --export` from standard input and adds those
store paths to the Nix store. Paths that already exist in the Nix store
are ignored. If a path refers to another path that doesn’t exist in the
Nix store, the import fails.
# Operation `--optimise`
## Synopsis
nix-store
\--optimise
## Description
The operation `--optimise` reduces Nix store disk space usage by finding
identical files in the store and hard-linking them to each other. It
typically reduces the size of the store by something like 25-35%. Only
regular files and symlinks are hard-linked in this manner. Files are
considered identical when they have the same NAR archive serialisation:
that is, regular files must have the same contents and permission
(executable or non-executable), and symlinks must have the same
contents.
After completion, or when the command is interrupted, a report on the
achieved savings is printed on standard error.
Use `-vv` or `-vvv` to get some progress indication.
## Example
$ nix-store --optimise
hashing files in `/nix/store/qhqx7l2f1kmwihc9bnxs7rc159hsxnf3-gcc-4.1.1'
...
541838819 bytes (516.74 MiB) freed by hard-linking 54143 files;
there are 114486 files with equal contents out of 215894 files in total
# Operation `--read-log`
## Synopsis
nix-store
\--read-log
\-l
paths
## Description
The operation `--read-log` prints the build log of the specified store
paths on standard output. The build log is whatever the builder of a
derivation wrote to standard output and standard error. If a store path
is not a derivation, the deriver of the store path is used.
Build logs are kept in `/nix/var/log/nix/drvs`. However, there is no
guarantee that a build log is available for any particular store path.
For instance, if the path was downloaded as a pre-built binary through a
substitute, then the log is unavailable.
## Example
$ nix-store -l $(which ktorrent)
building /nix/store/dhc73pvzpnzxhdgpimsd9sw39di66ph1-ktorrent-2.2.1
unpacking sources
unpacking source archive /nix/store/p8n1jpqs27mgkjw07pb5269717nzf5f8-ktorrent-2.2.1.tar.gz
ktorrent-2.2.1/
ktorrent-2.2.1/NEWS
...
# Operation `--dump-db`
## Synopsis
nix-store
\--dump-db
paths
## Description
The operation `--dump-db` writes a dump of the Nix database to standard
output. It can be loaded into an empty Nix store using `--load-db`. This
is useful for making backups and when migrating to different database
schemas.
By default, `--dump-db` will dump the entire Nix database. When one or
more store paths is passed, only the subset of the Nix database for
those store paths is dumped. As with `--export`, the user is responsible
for passing all the store paths for a closure. See `--export` for an
example.
# Operation `--load-db`
## Synopsis
nix-store
\--load-db
## Description
The operation `--load-db` reads a dump of the Nix database created by
`--dump-db` from standard input and loads it into the Nix database.
# Operation `--print-env`
## Synopsis
nix-store
\--print-env
drvpath
## Description
The operation `--print-env` prints out the environment of a derivation
in a format that can be evaluated by a shell. The command line arguments
of the builder are placed in the variable `_args`.
## Example
$ nix-store --print-env $(nix-instantiate '<nixpkgs>' -A firefox)
…
export src; src='/nix/store/plpj7qrwcz94z2psh6fchsi7s8yihc7k-firefox-12.0.source.tar.bz2'
export stdenv; stdenv='/nix/store/7c8asx3yfrg5dg1gzhzyq2236zfgibnn-stdenv'
export system; system='x86_64-linux'
export _args; _args='-e /nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25c-default-builder.sh'
# Operation `--generate-binary-cache-key`
## Synopsis
nix-store
\--generate-binary-cache-key
key-name
secret-key-file
public-key-file
## Description
This command generates an [Ed25519 key pair](http://ed25519.cr.yp.to/)
that can be used to create a signed binary cache. It takes three
mandatory parameters:
1. A key name, such as `cache.example.org-1`, that is used to look up
keys on the client when it verifies signatures. It can be anything,
but it’s suggested to use the host name of your cache (e.g.
`cache.example.org`) with a suffix denoting the number of the key
(to be incremented every time you need to revoke a key).
2. The file name where the secret key is to be stored.
3. The file name where the public key is to be stored.
# Environment variables

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\--help
\--version
\--verbose
\-v
\--quiet
\--log-format
format
\--no-build-output
\-Q
\--max-jobs
\-j
number
\--cores
number
\--max-silent-time
number
\--timeout
number
\--keep-going
\-k
\--keep-failed
\-K
\--fallback
\--readonly-mode
\-I
path
\--option
name
value

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\--prebuilt-only
\-b
\--attr
\-A
\--from-expression
\-E
\--from-profile
path