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diff --git a/doc/manual/packages/profiles.xml b/doc/manual/packages/profiles.xml deleted file mode 100644 index 3b8c5e293..000000000 --- a/doc/manual/packages/profiles.xml +++ /dev/null @@ -1,154 +0,0 @@ -<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-profiles"> - -<title>Profiles</title> - -<para>Profiles and user environments are Nix’s mechanism for -implementing the ability to allow different users to have different -configurations, and to do atomic upgrades and rollbacks. To -understand how they work, it’s useful to know a bit about how Nix -works. In Nix, packages are stored in unique locations in the -<emphasis>Nix store</emphasis> (typically, -<filename>/nix/store</filename>). For instance, a particular version -of the Subversion package might be stored in a directory -<filename>/nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3/</filename>, -while another version might be stored in -<filename>/nix/store/5mq2jcn36ldlmh93yj1n8s9c95pj7c5s-subversion-1.1.2</filename>. -The long strings prefixed to the directory names are cryptographic -hashes (to be precise, 160-bit truncations of SHA-256 hashes encoded -in a base-32 notation) of <emphasis>all</emphasis> inputs involved in -building the package — sources, dependencies, compiler flags, and so -on. So if two packages differ in any way, they end up in different -locations in the file system, so they don’t interfere with each other. -Here is what a part of a typical Nix store looks like:</para> - -<mediaobject> - <imageobject> - <imagedata fileref='../figures/user-environments.png' format='PNG' /> - </imageobject> -</mediaobject> - -<para>Of course, you wouldn’t want to type - -<screen> -$ /nix/store/dpmvp969yhdq...-subversion-1.1.3/bin/svn</screen> - -every time you want to run Subversion. Of course we could set up the -<literal>PATH</literal> environment variable to include the -<filename>bin</filename> directory of every package we want to use, -but this is not very convenient since changing <literal>PATH</literal> -doesn’t take effect for already existing processes. The solution Nix -uses is to create directory trees of symlinks to -<emphasis>activated</emphasis> packages. These are called -<emphasis>user environments</emphasis> and they are packages -themselves (though automatically generated by -<command>nix-env</command>), so they too reside in the Nix store. For -instance, in the figure above, the user environment -<filename>/nix/store/0c1p5z4kda11...-user-env</filename> contains a -symlink to just Subversion 1.1.2 (arrows in the figure indicate -symlinks). This would be what we would obtain if we had done - -<screen> -$ nix-env -i subversion</screen> - -on a set of Nix expressions that contained Subversion 1.1.2.</para> - -<para>This doesn’t in itself solve the problem, of course; you -wouldn’t want to type -<filename>/nix/store/0c1p5z4kda11...-user-env/bin/svn</filename> -either. That’s why there are symlinks outside of the store that point -to the user environments in the store; for instance, the symlinks -<filename>default-42-link</filename> and -<filename>default-43-link</filename> in the example. These are called -<emphasis>generations</emphasis> since every time you perform a -<command>nix-env</command> operation, a new user environment is -generated based on the current one. For instance, generation 43 was -created from generation 42 when we did - -<screen> -$ nix-env -i subversion firefox</screen> - -on a set of Nix expressions that contained Firefox and a new version -of Subversion.</para> - -<para>Generations are grouped together into -<emphasis>profiles</emphasis> so that different users don’t interfere -with each other if they don’t want to. For example: - -<screen> -$ ls -l /nix/var/nix/profiles/ -... -lrwxrwxrwx 1 eelco ... default-42-link -> /nix/store/0c1p5z4kda11...-user-env -lrwxrwxrwx 1 eelco ... default-43-link -> /nix/store/3aw2pdyx2jfc...-user-env -lrwxrwxrwx 1 eelco ... default -> default-43-link</screen> - -This shows a profile called <filename>default</filename>. The file -<filename>default</filename> itself is actually a symlink that points -to the current generation. When we do a <command>nix-env</command> -operation, a new user environment and generation link are created -based on the current one, and finally the <filename>default</filename> -symlink is made to point at the new generation. This last step is -atomic on Unix, which explains how we can do atomic upgrades. (Note -that the building/installing of new packages doesn’t interfere in -any way with old packages, since they are stored in different -locations in the Nix store.)</para> - -<para>If you find that you want to undo a <command>nix-env</command> -operation, you can just do - -<screen> -$ nix-env --rollback</screen> - -which will just make the current generation link point at the previous -link. E.g., <filename>default</filename> would be made to point at -<filename>default-42-link</filename>. You can also switch to a -specific generation: - -<screen> -$ nix-env --switch-generation 43</screen> - -which in this example would roll forward to generation 43 again. You -can also see all available generations: - -<screen> -$ nix-env --list-generations</screen></para> - -<para>You generally wouldn’t have -<filename>/nix/var/nix/profiles/<emphasis>some-profile</emphasis>/bin</filename> -in your <literal>PATH</literal>. Rather, there is a symlink -<filename>~/.nix-profile</filename> that points to your current -profile. This means that you should put -<filename>~/.nix-profile/bin</filename> in your <literal>PATH</literal> -(and indeed, that’s what the initialisation script -<filename>/nix/etc/profile.d/nix.sh</filename> does). This makes it -easier to switch to a different profile. You can do that using the -command <command>nix-env --switch-profile</command>: - -<screen> -$ nix-env --switch-profile /nix/var/nix/profiles/my-profile - -$ nix-env --switch-profile /nix/var/nix/profiles/default</screen> - -These commands switch to the <filename>my-profile</filename> and -default profile, respectively. If the profile doesn’t exist, it will -be created automatically. You should be careful about storing a -profile in another location than the <filename>profiles</filename> -directory, since otherwise it might not be used as a root of the -garbage collector (see <xref linkend='sec-garbage-collection' -/>).</para> - -<para>All <command>nix-env</command> operations work on the profile -pointed to by <command>~/.nix-profile</command>, but you can override -this using the <option>--profile</option> option (abbreviation -<option>-p</option>): - -<screen> -$ nix-env -p /nix/var/nix/profiles/other-profile -i subversion</screen> - -This will <emphasis>not</emphasis> change the -<command>~/.nix-profile</command> symlink.</para> - -</chapter> |