doc/manual/packages/sharing-packages.xml


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<chapter xmlns="http://docbook.org/ns/docbook"
      xmlns:xlink="http://www.w3.org/1999/xlink"
      xmlns:xi="http://www.w3.org/2001/XInclude"
      version="5.0"
      xml:id="sec-sharing-packages">

<title>Sharing Packages Between Machines</title>

<para>Sometimes you want to copy a package from one machine to
another.  Or, you want to install some packages and you know that
another machine already has some or all of those packages or their
dependencies.  In that case there are mechanisms to quickly copy
packages between machines.</para>

<para>The command <command
linkend="sec-nix-copy-closure">nix-copy-closure</command> copies a Nix
store path along with all its dependencies to or from another machine
via the SSH protocol.  It doesn’t copy store paths that are already
present on the target machine.  For example, the following command
copies Firefox with all its dependencies:

<screen>
$ nix-copy-closure --to alice@itchy.example.org $(type -p firefox)</screen>

See <xref linkend='sec-nix-copy-closure' /> for details.</para>

<para>With <command linkend='refsec-nix-store-export'>nix-store
--export</command> and <command
linkend='refsec-nix-store-import'>nix-store --import</command> you can
write the closure of a store path (that is, the path and all its
dependencies) to a file, and then unpack that file into another Nix
store.  For example,

<screen>
$ nix-store --export $(nix-store -qR $(type -p firefox)) > firefox.closure</screen>

writes the closure of Firefox to a file.  You can then copy this file
to another machine and install the closure:

<screen>
$ nix-store --import &lt; firefox.closure</screen>

Any store paths in the closure that are already present in the target
store are ignored.  It is also possible to pipe the export into
another command, e.g. to copy and install a closure directly to/on
another machine:

<screen>
$ nix-store --export $(nix-store -qR $(type -p firefox)) | bzip2 | \
    ssh alice@itchy.example.org "bunzip2 | nix-store --import"</screen>

But note that <command>nix-copy-closure</command> is generally more
efficient in this example because it only copies paths that are not
already present in the target Nix store.</para>

<para>Finally, if you can mount the Nix store of a remote machine in
your local filesystem, Nix can copy paths from the remote Nix store to
the local Nix store <emphasis>on demand</emphasis>.  For instance,
suppose that you mount a remote machine containing a Nix store via
<command
xlink:href="http://fuse.sourceforge.net/sshfs.html">sshfs</command>:

<screen>
$ sshfs alice@itchy.example.org:/ /mnt</screen>

You should then set the <envar>NIX_OTHER_STORES</envar> environment
variable to tell Nix about this remote Nix store:

<screen>
$ export NIX_OTHER_STORES=/mnt/nix</screen>

Then if you do any Nix operation, e.g.

<screen>
$ nix-env -i firefox</screen>

and Nix has to build a path that it sees is already present in
<filename>/mnt/nix</filename>, then it will just copy from there
instead of building it from source.</para>


</chapter>