* Documented multi-user Nix.
This commit is contained in:
Eelco Dolstra
parent
e007b50eb7
commit
fa44e401a8
5 changed files with 274 additions and 46 deletions
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@ -263,6 +263,17 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
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</varlistentry>
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<varlistentry xml:id="envar-remote"><term><envar>NIX_REMOTE</envar></term>
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<listitem><para>This variable should be set to
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<literal>daemon</literal> if you want to use the Nix daemon to
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executed Nix operations, which is necessary in <link
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linkend="ssec-multi-user">multi-user Nix installations</link>.
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Otherwise, it should be left unset.</para></listitem>
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</varlistentry>
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</variablelist>
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@ -100,14 +100,16 @@ ubiquitous 2.5.4a won't. Note that these are only required if you
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modify the parser or when you are building from the Subversion
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repository.</para>
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<para>Nix uses Sleepycat's Berkeley DB and CWI's ATerm library. These
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are included in the Nix source distribution. If you build from the
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Subversion repository, you must download them yourself and place them
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in the <filename>externals/</filename> directory. See
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<para>Nix uses Sleepycat's Berkeley DB, CWI's ATerm library and the
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bzip2 compressor (including the bzip2 library). These are included in
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the Nix source distribution. If you build from the Subversion
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repository, you must download them yourself and place them in the
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<filename>externals/</filename> directory. See
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<filename>externals/Makefile.am</filename> for the precise URLs of
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these packages. Alternatively, if you already have them installed,
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you can use <command>configure</command>'s <option>--with-bdb</option>
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and <option>--with-aterm</option> options to point to their respective
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you can use <command>configure</command>'s
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<option>--with-bdb</option>, <option>--with-aterm</option> and
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<option>--with-bzip2</option> options to point to their respective
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locations. Note that Berkeley DB <emphasis>must</emphasis> be version
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4.5; other versions may not have compatible database formats.</para>
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@ -118,19 +120,21 @@ locations. Note that Berkeley DB <emphasis>must</emphasis> be version
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<para>After unpacking or checking out the Nix sources, issue the
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following commands:
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</para>
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<screen>
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$ ./configure <replaceable>options...</replaceable>
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$ make
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$ make install</screen>
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<para>When building from the Subversion repository, these should be
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preceded by the command:
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</para>
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<para>When building from the Subversion repository, these should be
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preceded by the command:
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<screen>
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$ ./boostrap</screen>
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$ ./bootstrap</screen>
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</para>
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<para>The installation path can be specified by passing the
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<option>--prefix=<replaceable>prefix</replaceable></option> to
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@ -165,20 +169,24 @@ Hat Linux. They have been known to work work on SuSE Linux 8.1 and
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distribution based on <literal>glibc</literal> 2.3 or later.</para>
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<para>Once downloaded, the RPMs can be installed or upgraded using
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<command>rpm -U</command>. For example,</para>
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<command>rpm -U</command>. For example,
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<screen>
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$ rpm -U nix-0.5pre664-1.i386.rpm</screen>
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</para>
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<para>The RPMs install into the directory <filename>/nix</filename>.
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Nix can be uninstalled using <command>rpm -e nix</command>. After
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this it will be necessary to manually remove the Nix store and other
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auxiliary data:</para>
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auxiliary data:
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<screen>
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$ rm -rf /nix/store
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$ rm -rf /nix/var</screen>
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</para>
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</section>
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@ -231,33 +239,215 @@ class="username">root</systemitem> all the time.</para>
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</section>
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<section><title>Multi-user mode</title>
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<section xml:id="ssec-multi-user"><title>Multi-user mode</title>
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<para></para>
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<para>To allow a Nix store to be shared safely among multiple users,
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it is important that users are not able to run builders that modify
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the Nix store or database in arbitrary ways, or that interfere with
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builds started by other users. If they could do so, they could
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install a Trojan horse in some package and compromise the accounts of
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other users.</para>
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<!--
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warning: the nix-builders group should contain *only* the Nix
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builders, and nothing else. If the Nix account is compromised, you
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can execute programs under the accounts in the nix-builders group, so
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it obviously shouldn’t contain any “real” user accounts. So don’t use
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an existing group like <literal>users</literal> — just create a new
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one.
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-->
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<para>To prevent this, the Nix store and database are owned by some
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privileged user (usually <literal>root</literal>) and builders are
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executed under special user accounts (usually named
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<literal>nixbld1</literal>, <literal>nixbld2</literal>, etc.). When a
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unprivileged user runs a Nix command, actions that operate on the Nix
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store (such as builds) are forwarded to a <emphasis>Nix
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daemon</emphasis> running under the owner of the Nix store/database
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that performs the operation.</para>
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<note><para>Multi-user mode has one important limitation: only
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<systemitem class="username">root</systemitem> can run <command
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linkend="sec-nix-pull">nix-pull</command> to register the availability
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of pre-built binaries. However, those registrations
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<emphasis>are</emphasis> used by all users to speed up
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builds.</para></note>
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of pre-built binaries. However, those registrations are shared by all
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users, so they still get the benefit from <command>nix-pull</command>s
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done by <systemitem class="username">root</systemitem>.</para></note>
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<section><title>Setting up the build users</title>
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<para>The <emphasis>build users</emphasis> are the special UIDs under
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which builds are performed. They should all be members of the
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<emphasis>build users group</emphasis> (usually called
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<literal>nixbld</literal>). This group should have no other members.
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The build users should not be members of any other group.</para>
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<para>Here is a typical <filename>/etc/group</filename> definition of
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the build users group with 10 build users:
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<programlisting>
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nixbld:!:30000:nixbld1,nixbld2,nixbld3,nixbld4,nixbld5,nixbld6,nixbld7,nixbld8,nixbld9,nixbld10
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</programlisting>
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In this example the <literal>nixbld</literal> group has UID 30000, but
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of course it can be anything that doesn’t collide with an existing
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group.</para>
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<para>Here is the corresponding part of
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<filename>/etc/passwd</filename>:
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<programlisting>
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nixbld1:x:30001:65534:Nix build user 1:/var/empty:/noshell
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nixbld2:x:30002:65534:Nix build user 2:/var/empty:/noshell
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nixbld3:x:30003:65534:Nix build user 3:/var/empty:/noshell
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...
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nixbld10:x:30010:65534:Nix build user 10:/var/empty:/noshell
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</programlisting>
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The home directory of the build users should not exist or should be an
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empty directory to which they do not have write access.</para>
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<para>The build users should have write access to the Nix store, but
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they should not have the right to delete files. Thus the Nix store’s
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group should be the build users group, and it should have the sticky
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bit turned on (like <filename>/tmp</filename>):
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<screen>
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$ chgrp nixbld /nix/store
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$ chmod 1777 /nix/store
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</screen>
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</para>
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<para>Finally, you should tell Nix to use the build users by
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specifying the build users group in the <link
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linkend="conf-build-users-group"><literal>build-users-group</literal>
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option</link> in the <link linkend="sec-conf-file">Nix configuration
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file</link> (<literal>/nix/etc/nix/nix.conf</literal>):
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<programlisting>
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build-users-group = nixbld
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</programlisting>
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</para>
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</section>
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</section> <!-- end of permissions section -->
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<section><title>Nix store/database owned by root</title>
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<para>The simplest setup is to let <literal>root</literal> own the Nix
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store and database. I.e.,
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<screen>
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$ chown -R root /nix/store /nix/var/nix</screen>
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</para>
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<para>The Nix daemon should be started as follows (as
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<literal>root</literal>):
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<screen>
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$ nix-worker --daemon</screen>
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You’ll want to put that line somewhere in your system’s boot
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scripts.</para>
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<para>To let unprivileged users use the daemon, they should set the
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<link linkend="envar-remote"><envar>NIX_REMOTE</envar> environment
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variable</link> to <literal>daemon</literal>. So you should put a
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line like
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<programlisting>
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export NIX_REMOTE=daemon</programlisting>
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into the users’ login scripts.</para>
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</section>
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<section><title>Nix store/database not owned by root</title>
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<para>It is also possible to let the Nix store and database be owned
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by a non-root user, which should be more secure<footnote><para>Note
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however that even when the Nix daemon runs as root, not
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<emphasis>that</emphasis> much code is executed as root: Nix
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expression evaluation is performed by the calling (unprivileged) user,
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and builds are performed under the special build user accounts. So
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only the code that accesses the database and starts builds is executed
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as <literal>root</literal>.</para></footnote>. Typically, this user
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is a special account called <literal>nix</literal>, but it can be
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named anything. It should own the Nix store and database:
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<screen>
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$ chown -R root /nix/store /nix/var/nix</screen>
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and of course <command>nix-worker --daemon</command> should be started
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under that user, e.g.,
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<screen>
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$ su - nix -c "exec /nix/bin/nix-worker --daemon"</screen>
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</para>
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<para>There is a catch, though: non-<literal>root</literal> users
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cannot start builds under the build user accounts, since the
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<function>setuid</function> system call is obviously privileged. To
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allow a non-<literal>root</literal> Nix daemon to use the build user
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feature, it calls a setuid-root helper program,
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<command>nix-setuid-helper</command>. This program is installed in
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<filename><replaceable>prefix</replaceable>/libexec/nix-setuid-helper</filename>.
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To set the permissions properly (Nix’s <command>make install</command>
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doesn’t do this, since we don’t want to ship setuid-root programs
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out-of-the-box):
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<screen>
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$ chown root.root /nix/libexec/nix-setuid-helper
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$ chmod 4755 /nix/libexec/nix-setuid-helper
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</screen>
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(This example assumes that the Nix binaries are installed in
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<filename>/nix</filename>.)</para>
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<para>Of course, the <command>nix-setuid-helper</command> command
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should not be usable by just anybody, since then anybody could run
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commands under the Nix build user accounts. For that reason there is
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a configuration file <filename>/etc/nix-setuid.conf</filename> that
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restricts the use of the helper. This file should be a text file
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containing precisely two lines, the first being the Nix daemon user
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and the second being the build users group, e.g.,
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<programlisting>
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nix
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nixbld
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</programlisting>
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The setuid-helper barfs if it is called by a user other than the one
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specified on the first line, or if it is asked to execute a build
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under a user who is not a member of the group specified on the second
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line. The file <filename>/etc/nix-setuid.conf</filename> must be
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owned by root, and must not be group- or world-writable. The
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setuid-helper barfs if this is not the case.</para>
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</section>
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<section><title>Restricting access</title>
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<para>To limit which users can perform Nix operations, you can use the
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permissions on the directory
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<filename>/nix/var/nix/daemon-socket</filename>. For instance, if you
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want to restrict the use of Nix to the members of a group called
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<literal>nix-users</literal>, do
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<screen>
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$ chgrp nix-users /nix/var/nix/daemon-socket
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$ chmod ug=rwx,o= /nix/var/nix/daemon-socket
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</screen>
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This way, users who are not in the <literal>nix-users</literal> group
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cannot connect to the Unix domain socket
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<filename>/nix/var/nix/daemon-socket/socket</filename>, so they cannot
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perform Nix operations.</para>
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</section>
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</section> <!-- end of multi-user -->
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</section> <!-- end of security -->
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<section><title>Using Nix</title>
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@ -19,13 +19,6 @@
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<command>nix-env</command>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-common-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
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<arg><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--attr</option></arg>
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<arg choice='plain'><option>-A</option></arg>
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</group>
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<replaceable>attrPath</replaceable>
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</arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--file</option></arg>
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@ -45,9 +38,6 @@
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<replaceable>system</replaceable>
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</arg>
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<arg><option>--dry-run</option></arg>
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<arg><option>--from-expression</option></arg>
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<arg><option>-E</option></arg>
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<arg><option>--from-profile</option> <replaceable>path</replaceable></arg>
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<arg choice='plain'><replaceable>operation</replaceable></arg>
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<arg rep='repeat'><replaceable>options</replaceable></arg>
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<arg rep='repeat'><replaceable>arguments</replaceable></arg>
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@ -190,6 +180,7 @@ linkend="sec-common-options" />.</para>
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<arg choice='plain'><option>--install</option></arg>
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<arg choice='plain'><option>-i</option></arg>
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</group>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-inst-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
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<group choice='opt'>
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<arg choice='plain'><option>--preserve-installed</option></arg>
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<arg choice='plain'><option>-P</option></arg>
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@ -397,6 +388,7 @@ the following paths will be substituted:
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<arg choice='plain'><option>--upgrade</option></arg>
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<arg choice='plain'><option>-u</option></arg>
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</group>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-inst-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
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<group choice='opt'>
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<arg choice='plain'><option>--lt</option></arg>
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<arg choice='plain'><option>--leq</option></arg>
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@ -592,25 +584,21 @@ $ nix-env -e '*' <lineannotation>(remove everything)</lineannotation></screen>
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<arg choice='plain'><option>--query</option></arg>
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<arg choice='plain'><option>-q</option></arg>
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</group>
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<arg><option>--xml</option></arg>
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<group choice='opt'>
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<arg choice='plain'><option>--installed</option></arg>
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<arg choice='plain'><option>--available</option></arg>
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<arg choice='plain'><option>-a</option></arg>
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</group>
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<sbr />
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--status</option></arg>
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<arg choice='plain'><option>-s</option></arg>
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</group>
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</arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--attr</option></arg>
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<arg choice='plain'><option>-A</option></arg>
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</group>
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</arg>
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<arg><option>--attr-path</option></arg>
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<arg><option>--no-name</option></arg>
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<arg>
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<group choice='req'>
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@ -622,6 +610,27 @@ $ nix-env -e '*' <lineannotation>(remove everything)</lineannotation></screen>
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<arg><option>--drv-path</option></arg>
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<arg><option>--out-path</option></arg>
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<arg><option>--description</option></arg>
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<arg><option>--meta</option></arg>
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<sbr />
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<arg><option>--xml</option></arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--prebuilt-only</option></arg>
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<arg choice='plain'><option>-b</option></arg>
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</group>
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</arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--attr</option></arg>
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<arg choice='plain'><option>-A</option></arg>
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</group>
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<replaceable>attribute-path</replaceable>
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</arg>
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<sbr />
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<arg choice='plain' rep='repeat'><replaceable>names</replaceable></arg>
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</cmdsynopsis>
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15
doc/manual/opt-inst-syn.xml
Normal file
15
doc/manual/opt-inst-syn.xml
Normal file
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@ -0,0 +1,15 @@
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<nop xmlns="http://docbook.org/ns/docbook">
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--attr</option></arg>
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<arg choice='plain'><option>-A</option></arg>
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</group>
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</arg>
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<arg><option>--from-expression</option></arg>
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||||
<arg><option>-E</option></arg>
|
||||
|
||||
<arg><option>--from-profile</option> <replaceable>path</replaceable></arg>
|
||||
|
||||
</nop>
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||||
|
|
@ -789,6 +789,7 @@ static Expr prim_listToAttrs(EvalState & state, const ATermVector & args)
|
|||
}
|
||||
}
|
||||
|
||||
|
||||
static Expr prim_removeAttrs(EvalState & state, const ATermVector & args)
|
||||
{
|
||||
ATermMap attrs;
|
||||
|
|
@ -803,6 +804,7 @@ static Expr prim_removeAttrs(EvalState & state, const ATermVector & args)
|
|||
return makeAttrs(attrs);
|
||||
}
|
||||
|
||||
|
||||
/* Determine whether the argument is a list. */
|
||||
static Expr prim_isAttrs(EvalState & state, const ATermVector & args)
|
||||
{
|
||||
|
|
@ -810,6 +812,7 @@ static Expr prim_isAttrs(EvalState & state, const ATermVector & args)
|
|||
return makeBool(matchAttrs(evalExpr(state, args[0]), list));
|
||||
}
|
||||
|
||||
|
||||
/*************************************************************
|
||||
* Lists
|
||||
*************************************************************/
|
||||
|
|
|
|||
Loading…
Reference in a new issue