<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-user-management">

<title>User Management</title>

<para>NixOS supports both declarative and imperative styles of user
management.  In the declarative style, users are specified in
<filename>configuration.nix</filename>.  For instance, the following
states that a user account named <literal>alice</literal> shall exist:

<programlisting>
users.extraUsers.alice =
  { isNormalUser = true;
    home = "/home/alice";
    description = "Alice Foobar";
    extraGroups = [ "wheel" "networkmanager" ];
    openssh.authorizedKeys.keys = [ "ssh-dss AAAAB3Nza... alice@foobar" ];
  };
</programlisting>

Note that <literal>alice</literal> is a member of the
<literal>wheel</literal> and <literal>networkmanager</literal> groups,
which allows her to use <command>sudo</command> to execute commands as
<literal>root</literal> and to configure the network, respectively.
Also note the SSH public key that allows remote logins with the
corresponding private key. Users created in this way do not have a
password by default, so they cannot log in via mechanisms that require
a password. However, you can use the <command>passwd</command> program
to set a password, which is retained across invocations of
<command>nixos-rebuild</command>.</para>

<para>If you set users.mutableUsers to false, then the contents of /etc/passwd
and /etc/group will be congruent to your NixOS configuration. For instance,
if you remove a user from users.extraUsers and run nixos-rebuild, the user
account will cease to exist. Also, imperative commands for managing users
and groups, such as useradd, are no longer available. Passwords may still be
assigned by setting the user's <literal>hashedPassword</literal> option. A
hashed password can be generated using <command>mkpasswd -m sha-512</command>
after installing the <literal>mkpasswd</literal> package.</para>

<para>A user ID (uid) is assigned automatically.  You can also specify
a uid manually by adding

<programlisting>
    uid = 1000;
</programlisting>

to the user specification.</para>

<para>Groups can be specified similarly.  The following states that a
group named <literal>students</literal> shall exist:

<programlisting>
users.extraGroups.students.gid = 1000;
</programlisting>

As with users, the group ID (gid) is optional and will be assigned
automatically if it’s missing.</para>

<para>In the imperative style, users and groups are managed by
commands such as <command>useradd</command>,
<command>groupmod</command> and so on.  For instance, to create a user
account named <literal>alice</literal>:

<screen>
# useradd -m alice</screen>

To make all nix tools available to this new user use `su - USER` which 
opens a login shell (==shell that loads the profile) for given user. 
This will create the ~/.nix-defexpr symlink. So run:

<screen>
# su - alice -c "true"</screen>


The flag <option>-m</option> causes the creation of a home directory
for the new user, which is generally what you want.  The user does not
have an initial password and therefore cannot log in.  A password can
be set using the <command>passwd</command> utility:

<screen>
# passwd alice
Enter new UNIX password: ***
Retype new UNIX password: ***
</screen>

A user can be deleted using <command>userdel</command>:

<screen>
# userdel -r alice</screen>

The flag <option>-r</option> deletes the user’s home directory.
Accounts can be modified using <command>usermod</command>.  Unix
groups can be managed using <command>groupadd</command>,
<command>groupmod</command> and <command>groupdel</command>.</para>

</chapter>
