use /sbin/nologin as the invalid shell, good idea by tholo

src/etc/master.passwd

@@ -1,9 +1,9 @@
 root::0:0::0:0:Charlie &:/root:/bin/csh
-toor:*:0:0::0:0:Bourne-again Superuser:/root:/dev/null
-daemon:*:1:31::0:0:The devil himself:/root:/dev/null
-operator:*:2:20::0:0:System &:/usr/guest/operator:/dev/null
-bin:*:3:7::0:0:Binaries Commands and Source,,,:/:/dev/null
-games:*:7:13::0:0:Games pseudo-user:/usr/games:/dev/null
+toor:*:0:0::0:0:Bourne-again Superuser:/root:/sbin/nologin
+daemon:*:1:31::0:0:The devil himself:/root:/sbin/nologin
+operator:*:2:20::0:0:System &:/usr/guest/operator:/sbin/nologin
+bin:*:3:7::0:0:Binaries Commands and Source,,,:/:/sbin/nologin
+games:*:7:13::0:0:Games pseudo-user:/usr/games:/sbin/nologin
 uucp:*:66:1::0:0:UNIX-to-UNIX Copy:/var/spool/uucppublic:/usr/libexec/uucp/uucico
-nobody:*:32767:9999::0:0:Unprivileged user:/nonexistent:/dev/null
-ingres:*:267:74::0:0:& Group:/usr/ingres:/dev/null
+nobody:*:32767:9999::0:0:Unprivileged user:/nonexistent:/sbin/nologin
+ingres:*:267:74::0:0:& Group:/usr/ingres:/sbin/nologin