Generate /etc/passwd and /etc/group at build time

This is a rather large commit that switches user/group creation from using
useradd/groupadd on activation to just generating the contents of /etc/passwd
and /etc/group, and then on activation merging the generated files with the
files that exist in the system. This makes the user activation process much
cleaner, in my opinion.

The users.extraUsers.<user>.uid and users.extraGroups.<group>.gid must all be
properly defined (if <user>.createUser is true, which it is by default). My
pull request adds a lot of uids/gids to config.ids to solve this problem for
existing nixos services, but there might be configurations that break because
this change. However, this will be discovered during the build.

Option changes introduced by this commit:

* Remove the options <user>.isSystemUser and <user>.isAlias since
they don't make sense when generating /etc/passwd statically.

* Add <group>.members as a complement to <user>.extraGroups.

* Add <user>.passwordFile for setting a user's password from an encrypted
(shadow-style) file.

* Add users.mutableUsers which is true by default. This means you can keep
managing your users as previously, by using useradd/groupadd manually. This is
accomplished by merging the generated passwd/group file with the existing files
in /etc on system activation. The merging of the files is simplistic. It just
looks at the user/group names. If a user/group exists both on the system and
in the generated files, the system entry will be kept un-changed and the
generated entries will be ignored. The merging itself is performed with the
help of vipw/vigr to properly lock the account files during edit.
If mutableUsers is set to false, the generated passwd and group files will not
be merged with the system files on activation. Instead they will simply replace
the system files, and overwrite any changes done on the running system. The
same logic holds for user password, if the <user>.password or
<user>.passwordFile options are used. If mutableUsers is false, password will
simply be replaced on activation. If true, the initial user passwords will be
set according to the configuration, but existing passwords will not be touched.

I have tested this on a couple of different systems and it seems to work fine
so far. If you think this is a good idea, please test it. This way of adding
local users has been discussed in issue #103 (and this commit solves that
issue).

1 files changed, 207 insertions, 168 deletions

diff --git a/nixos/modules/config/users-groups.nix b/nixos/modules/config/users-groups.nix
index 714de646eb7a..97bf67262795 100644
--- a/nixos/modules/config/users-groups.nix
+++ b/nixos/modules/config/users-groups.nix
@@ -5,7 +5,7 @@ with pkgs.lib;
 let
 
   ids = config.ids;
-  users = config.users;
+  cfg = config.users;
 
   userOpts = { name, config, ... }: {
 
@@ -28,9 +28,8 @@ let
       };
 
       uid = mkOption {
-        type = with types; uniq (nullOr int);
-        default = null;
-        description = "The account UID. If undefined, NixOS will select a free UID.";
+        type = with types; uniq int;
+        description = "The account UID.";
       };
 
       group = mkOption {
@@ -60,13 +59,21 @@ let
       createHome = mkOption {
         type = types.bool;
         default = false;
-        description = "If true, the home directory will be created automatically.";
+        description = ''
+          If true, the home directory will be created automatically. If this
+          option is true and the home directory already exists but is not
+          owned by the user, directory owner and group will be changed to
+          match the user.
+        '';
       };
 
       useDefaultShell = mkOption {
         type = types.bool;
         default = false;
-        description = "If true, the user's shell will be set to <literal>users.defaultUserShell</literal>.";
+        description = ''
+          If true, the user's shell will be set to
+          <literal>cfg.defaultUserShell</literal>.
+        '';
       };
 
       password = mkOption {
@@ -78,13 +85,29 @@ let
           because it is world-readable in the Nix store.  This option
           should only be used for public accounts such as
           <literal>guest</literal>.
+          The option <literal>password</literal> overrides
+          <literal>passwordFile</literal>, if both are specified.
+          If none of the options <literal>password</literal> or
+          <literal>passwordFile</literal> are specified, the user account will
+          be locked for password logins. This is the default behavior except
+          for the root account, which has an empty password by default. If you
+          want to lock the root account for password logins, set
+          <literal>users.extraUsers.root.password</literal> to
+          <literal>null</literal>.
         '';
       };
 
-      isSystemUser = mkOption {
-        type = types.bool;
-        default = true;
-        description = "Indicates if the user is a system user or not.";
+      passwordFile = mkOption {
+        type = with types; uniq (nullOr string);
+        default = null;
+        description = ''
+          The path to a file that contains the user's password. The password
+          file is read on each system activation. The file should contain
+          exactly one line, which should be the password in an encrypted form
+          that is suitable for the <literal>chpasswd -e</literal> command.
+          See the <literal>password</literal> for more details on how passwords
+          are assigned.
+        '';
       };
 
       createUser = mkOption {
@@ -96,19 +119,11 @@ let
           then not modify any of the basic properties for the user account.
         '';
       };
-
-      isAlias = mkOption {
-        type = types.bool;
-        default = false;
-        description = "If true, the UID of this user is not required to be unique and can thus alias another user.";
-      };
-
     };
 
     config = {
       name = mkDefault name;
-      uid = mkDefault (attrByPath [name] null ids.uids);
-      shell = mkIf config.useDefaultShell (mkDefault users.defaultUserShell);
+      shell = mkIf config.useDefaultShell (mkDefault cfg.defaultUserShell);
     };
 
   };
@@ -123,28 +138,100 @@ let
       };
 
       gid = mkOption {
-        type = with types; uniq (nullOr int);
-        default = null;
-        description = "The GID of the group. If undefined, NixOS will select a free GID.";
+        type = with types; uniq int;
+        description = "The GID of the group.";
+      };
+
+      members = mkOption {
+        type = with types; listOf string;
+        default = [];
+        description = ''
+        '';
       };
 
     };
 
     config = {
       name = mkDefault name;
-      gid = mkDefault (attrByPath [name] null ids.gids);
     };
 
   };
 
-  # Note: the 'X' in front of the password is to distinguish between
-  # having an empty password, and not having a password.
-  serializedUser = u: "${u.name}\n${u.description}\n${if u.uid != null then toString u.uid else ""}\n${u.group}\n${toString (concatStringsSep "," u.extraGroups)}\n${u.home}\n${u.shell}\n${toString u.createHome}\n${if u.password != null then "X" + u.password else ""}\n${toString u.isSystemUser}\n${toString u.createUser}\n${toString u.isAlias}\n";
-
-  usersFile = pkgs.writeText "users" (
+  getGroup = gname:
+    let
+      groups = mapAttrsToList (n: g: g) (
+        filterAttrs (n: g: g.name == gname) cfg.extraGroups
+      );
+    in
+      if length groups == 1 then head groups
+      else if groups == [] then throw "Group ${gname} not defined"
+      else throw "Group ${gname} has multiple definitions";
+
+  getUser = uname:
+    let
+      users = mapAttrsToList (n: u: u) (
+        filterAttrs (n: u: u.name == uname) cfg.extraUsers
+      );
+    in
+      if length users == 1 then head users
+      else if users == [] then throw "User ${uname} not defined"
+      else throw "User ${uname} has multiple definitions";
+
+  mkGroupEntry = gname:
     let
-      p = partition (u: u.isAlias) (attrValues config.users.extraUsers);
-    in concatStrings (map serializedUser p.wrong ++ map serializedUser p.right));
+      g = getGroup gname;
+      users = mapAttrsToList (n: u: u.name) (
+        filterAttrs (n: u: elem g.name u.extraGroups) cfg.extraUsers
+      );
+    in concatStringsSep ":" [
+      g.name "x" (toString g.gid)
+      (concatStringsSep "," (users ++ (filter (u: !(elem u users)) g.members)))
+    ];
+
+  mkPasswdEntry = uname: let u = getUser uname; in
+    concatStringsSep ":" [
+      u.name "x" (toString u.uid)
+      (toString (getGroup u.group).gid)
+      u.description u.home u.shell
+    ];
+
+  sortOn = a: sort (as1: as2: lessThan (getAttr a as1) (getAttr a as2));
+
+  groupFile = pkgs.writeText "group" (
+    concatStringsSep "\n" (map (g: mkGroupEntry g.name) (
+      sortOn "gid" (attrValues cfg.extraGroups)
+    ))
+  );
+
+  passwdFile = pkgs.writeText "passwd" (
+    concatStringsSep "\n" (map (u: mkPasswdEntry u.name) (
+      sortOn "uid" (filter (u: u.createUser) (attrValues cfg.extraUsers))
+    ))
+  );
+
+  # If mutableUsers is true, this script adds all users/groups defined in
+  # users.extra{Users,Groups} to /etc/{passwd,group} iff there isn't any
+  # existing user/group with the same name in those files.
+  # If mutableUsers is false, the /etc/{passwd,group} files will simply be
+  # replaced with the users/groups defined in the NixOS configuration.
+  # The merging procedure could certainly be improved, and instead of just
+  # keeping the lines as-is from /etc/{passwd,group} they could be combined
+  # in some way with the generated content from the NixOS configuration.
+  merger = src: pkgs.writeScript "merger" ''
+    #!${pkgs.bash}/bin/bash
+
+    PATH=${pkgs.gawk}/bin:${pkgs.gnugrep}/bin:$PATH
+
+    ${if !cfg.mutableUsers
+      then ''cp ${src} $1.tmp''
+      else ''awk -F: '{ print "^"$1":.*" }' $1 | egrep -vf - ${src} | cat $1 - > $1.tmp''
+    }
+
+    # set mtime to +1, otherwise change might go unnoticed (vipw/vigr only looks at mtime)
+    touch -m -t $(date -d @$(($(stat -c %Y $1)+1)) +%Y%m%d%H%M.%S) $1.tmp
+
+    mv -f $1.tmp $1
+  '';
 
 in
 
@@ -154,6 +241,28 @@ in
 
   options = {
 
+    users.mutableUsers = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        If true, you are free to add new users and groups to the system
+        with the ordinary <literal>useradd</literal> and
+        <literal>groupadd</literal> commands. On system activation, the
+        existing contents of the <literal>/etc/passwd</literal> and
+        <literal>/etc/group</literal> files will be merged with the
+        contents generated from the <literal>users.extraUsers</literal> and
+        <literal>users.extraGroups</literal> options. If
+        <literal>mutableUsers</literal> is false, the contents of the user and
+        group files will simply be replaced on system activation. This also
+        holds for the user passwords; if this option is false, all changed
+        passwords will be reset according to the
+        <literal>users.extraUsers</literal> configuration on activation. If
+        this option is true, the initial password for a user will be set
+        according to <literal>users.extraUsers</literal>, but existing passwords
+        will not be changed.
+      '';
+    };
+
     users.extraUsers = mkOption {
       default = {};
       type = types.loaOf types.optionSet;
@@ -188,20 +297,6 @@ in
       options = [ groupOpts ];
     };
 
-    security.initialRootPassword = mkOption {
-      type = types.str;
-      default = "";
-      example = "!";
-      description = ''
-        The (hashed) password for the root account set on initial
-        installation.  The empty string denotes that root can login
-        locally without a password (but not via remote services such
-        as SSH, or indirectly via <command>su</command> or
-        <command>sudo</command>).  The string <literal>!</literal>
-        prevents root from logging in using a password.
-      '';
-    };
-
   };
 
 
@@ -211,144 +306,88 @@ in
 
     users.extraUsers = {
       root = {
+        uid = ids.uids.root;
         description = "System administrator";
         home = "/root";
-        shell = config.users.defaultUserShell;
+        shell = cfg.defaultUserShell;
         group = "root";
+        password = mkDefault "";
       };
       nobody = {
+        uid = ids.uids.nobody;
         description = "Unprivileged account (don't use!)";
+        group = "nogroup";
       };
     };
 
     users.extraGroups = {
-      root = { };
-      wheel = { };
-      disk = { };
-      kmem = { };
-      tty = { };
-      floppy = { };
-      uucp = { };
-      lp = { };
-      cdrom = { };
-      tape = { };
-      audio = { };
-      video = { };
-      dialout = { };
-      nogroup = { };
-      users = { };
-      nixbld = { };
-      utmp = { };
-      adm = { }; # expected by journald
+      root.gid = ids.gids.root;
+      wheel.gid = ids.gids.wheel;
+      disk.gid = ids.gids.disk;
+      kmem.gid = ids.gids.kmem;
+      tty.gid = ids.gids.tty;
+      floppy.gid = ids.gids.floppy;
+      uucp.gid = ids.gids.uucp;
+      lp.gid = ids.gids.lp;
+      cdrom.gid = ids.gids.cdrom;
+      tape.gid = ids.gids.tape;
+      audio.gid = ids.gids.audio;
+      video.gid = ids.gids.video;
+      dialout.gid = ids.gids.dialout;
+      nogroup.gid = ids.gids.nogroup;
+      users.gid = ids.gids.users;
+      nixbld.gid = ids.gids.nixbld;
+      utmp.gid = ids.gids.utmp;
+      adm.gid = ids.gids.adm;
     };
 
-    system.activationScripts.rootPasswd = stringAfter [ "etc" ]
-      ''
-        # If there is no password file yet, create a root account with an
-        # empty password.
-        if ! test -e /etc/passwd; then
-            rootHome=/root
-            touch /etc/passwd; chmod 0644 /etc/passwd
-            touch /etc/group; chmod 0644 /etc/group
-            touch /etc/shadow; chmod 0600 /etc/shadow
-            # Can't use useradd, since it complains that it doesn't know us
-            # (bootstrap problem!).
-            echo "root:x:0:0:System administrator:$rootHome:${config.users.defaultUserShell}" >> /etc/passwd
-            echo "root:${config.security.initialRootPassword}:::::::" >> /etc/shadow
-        fi
-      '';
-
-    # Print a reminder for users to set a root password.
-    environment.interactiveShellInit =
-      ''
-        if [ "$UID" = 0 ]; then
-            read _l < /etc/shadow
-            if [ "''${_l:0:6}" = root:: ]; then
-                cat >&2 <<EOF
-        Warning: Your root account has a null password, allowing local users
-        to login as root.  Please set a non-null password using \`passwd', or
-        disable password-based root logins using \`passwd -l'.
-        EOF
-            fi
-            unset _l
-        fi
-      '';
-
-    system.activationScripts.users = stringAfter [ "groups" ]
-      ''
-        echo "updating users..."
-
-        cat ${usersFile} | while true; do
-            read name || break
-            read description
-            read uid
-            read group
-            read extraGroups
-            read home
-            read shell
-            read createHome
-            read password
-            read isSystemUser
-            read createUser
-            read isAlias
-
-            if [ -z "$createUser" ]; then
-                continue
-            fi
-
-            if ! curEnt=$(getent passwd "$name"); then
-                useradd ''${isSystemUser:+--system} \
-                    --comment "$description" \
-                    ''${uid:+--uid $uid} \
-                    --gid "$group" \
-                    --groups "$extraGroups" \
-                    --home "$home" \
-                    --shell "$shell" \
-                    ''${createHome:+--create-home} \
-                    ''${isAlias:+--non-unique} \
-                    "$name"
-                if test "''${password:0:1}" = 'X'; then
-                    (echo "''${password:1}"; echo "''${password:1}") | ${pkgs.shadow}/bin/passwd "$name"
-                fi
-            else
-                #echo "updating user $name..."
-                oldIFS="$IFS"; IFS=:; set -- $curEnt; IFS="$oldIFS"
-                prevUid=$3
-                prevHome=$6
-                # Don't change the home directory if it's the same to prevent
-                # unnecessary warnings about logged in users.
-                if test "$prevHome" = "$home"; then unset home; fi
-                usermod \
-                    --comment "$description" \
-                    --gid "$group" \
-                    --groups "$extraGroups" \
-                    ''${home:+--home "$home"} \
-                    --shell "$shell" \
-                    "$name"
-            fi
-
-        done
+    system.activationScripts.users =
+      let
+        mkhomeUsers = filterAttrs (n: u: u.createHome) cfg.extraUsers;
+        setpwUsers = filterAttrs (n: u: u.createUser) cfg.extraUsers;
+        setpw = n: u: ''
+          setpw=yes
+          ${optionalString cfg.mutableUsers ''
+            test "$(getent shadow '${u.name}' | cut -d: -f2)" != "x" && setpw=no
+          ''}
+          if [ "$setpw" == "yes" ]; then
+            ${if u.password == ""
+              then "passwd -d '${u.name}' &>/dev/null"
+              else if (isNull u.password && isNull u.passwordFile)
+              then "passwd -l '${u.name}' &>/dev/null"
+              else if !(isNull u.password)
+              then ''
+                echo "${u.name}:${u.password}" | ${pkgs.shadow}/sbin/chpasswd''
+              else ''
+                echo -n "${u.name}:" | cat - "${u.passwordFile}" | \
+                  ${pkgs.shadow}/sbin/chpasswd -e
+              ''
+            }
+          fi
+        '';
+        mkhome = n: u:
+         let
+            uid = toString u.uid;
+            gid = toString ((getGroup u.group).gid);
+            h = u.home;
+          in ''
+            test -a "${h}" || mkdir -p "${h}" || true
+            test "$(stat -c %u "${h}")" = ${uid} || chown ${uid} "${h}" || true
+            test "$(stat -c %g "${h}")" = ${gid} || chgrp ${gid} "${h}" || true
+          '';
+      in stringAfter [ "etc" ] ''
+        touch /etc/group
+        touch /etc/passwd
+        VISUAL=${merger groupFile} ${pkgs.shadow}/sbin/vigr &>/dev/null
+        VISUAL=${merger passwdFile} ${pkgs.shadow}/sbin/vipw &>/dev/null
+        ${pkgs.shadow}/sbin/grpconv
+        ${pkgs.shadow}/sbin/pwconv
+        ${concatStrings (mapAttrsToList mkhome mkhomeUsers)}
+        ${concatStrings (mapAttrsToList setpw setpwUsers)}
       '';
 
-    system.activationScripts.groups = stringAfter [ "rootPasswd" "binsh" "etc" "var" ]
-      ''
-        echo "updating groups..."
-
-        createGroup() {
-            name="$1"
-            gid="$2"
-
-            if ! curEnt=$(getent group "$name"); then
-                groupadd --system \
-                    ''${gid:+--gid $gid} \
-                    "$name"
-            fi
-        }
-
-        ${flip concatMapStrings (attrValues config.users.extraGroups) (g: ''
-          createGroup '${g.name}' '${toString g.gid}'
-        '')}
-      '';
+    # for backwards compatibility
+    system.activationScripts.groups = stringAfter [ "users" ] "";
 
   };