etc: synchronize master.password, group to NetBSD

IMPORTANT: this change has a docs/UPDATING entry!

This change is a long overdue switch-over from the old MINIX set of
user and group accounts to the NetBSD set.  This switch-over is
increasingly important now that we are importing more and more
utilities from NetBSD, several of which expect various user accounts
to exist.  By switching over in one go, we save ourselves various
headaches in the long run, even if the switch-over itself is a bit
painful for existing MINIX users.

The newly imported master.passwd and group files have three exceptions
compared to their NetBSD originals:

1. There is a custom "service" account for MINIX 3 services.  This
   account is used to limit run-time privileges of various system
   services, and is not used for any files on disk.  Its user ID may
   be changed later, but should always correspond to whatever the
   SERVICE_UID definition is set to.
2. The user "bin" has its shell set to /bin/sh, instead of NetBSD's
   /sbin/nologin.  The reason for this is that the test set in
   /usr/tests/minix-posix will not be able to run otherwise.
3. The group "operator" has been set to group ID 0, to match its old
   value.  This tweak is purely for transitioning purposes: as of
   writing, pkgsrc packages are still using root:operator as owner and
   group for most installed files.  Sometime later, we can change back
   "operator" to group ID 5 without breaking anything, because it does
   not appear that this group name is used for anything important.

Change-Id: I689bcfff4cf7ba85c27d1ae579057fa3f8019c68

docs/UPDATING

@@ -1,3 +1,77 @@
+20170218:
+	Before starting a build, you will have to update your master.passwd and
+	group files in /etc.  This is needed because we have switched over from
+	the old set of MINIX users and groups to the new set of NetBSD users
+	and groups, as needed by various imported tools.  Follow these steps.
+
+	1. Make a back-up copy of your old master.passwd and group files:
+
+		# cp /etc/master.passwd /etc/master.passwd~
+		# cp /etc/group /etc/group~
+
+	2. Install /usr/src/etc/master.passwd to /etc/master.passwd, and
+	   install /usr/src/etc/group to /etc/group.  If you have NOT created
+	   any local user accounts yourself, for example because you are
+	   upgrading a fresh MINIX 3 installation right away, all you need to
+	   do is copy over those two files:
+
+		# cp /usr/src/etc/master.passwd /etc/master.passwd
+		# cp /usr/src/etc/group /etc/group
+
+	   If you DO have custom user accounts or groups, you need to merge
+	   their lines (and only those!) into the new master.passwd and group
+	   files manually.  If you are unsure whether you have such custom
+	   entries, you can use the following commands:
+
+		# cd /usr/src
+		# git show 68804c2:etc/master.passwd | diff -u - /etc/master.passwd
+		# git show 68804c2:etc/group | diff -u - /etc/group
+
+	   This should show any changes compared to the old two templates.  If
+	   you have such changes, you need to reapply them after copying over
+	   the new two templates.  The following procedure shows one approach:
+
+		# cd /usr/src
+		# cp /etc/master.passwd /tmp/my-passwd
+		# vi /tmp/my-passwd
+		<remove any lines from /tmp/my-passwd that have no password>
+		# cp /usr/src/etc/master.passwd /etc/master.passwd
+		# cat /tmp/my-passwd >> /etc/master.passwd
+		# rm /tmp/my-passwd
+
+	   ..and follow a similar procedure for /etc/group.
+
+	3. Once the new files are in place, update all derived password files:
+
+		# pwd_mkdb -p /etc/master.passwd
+
+	   If you did everything right so far, the following command:
+
+		# postinstall check uid gid
+
+	   ..should show "postinstall checks passed: uid gid" and no failures.
+
+	4. Now perform a full build as usual:
+
+		# cd /usr/src
+		# make build
+
+	   As part of the build, all /dev files will get new proper ownership.
+
+	5. There may still be files that are owned by users and groups that now
+	   have been renumbered.  It is advisable to run at least the following
+	   three commands to apply the renumbering to the most common files:
+
+		# find / -user 2 -exec chown bin \{\} \;
+		# find / -user 5 -exec chown uucp \{\} \;
+		# find / -user 9998 -exec chown games \{\} \;
+
+	   If you have installed custom programs, you may want to check whether
+	   they are not affected by the change.  This should be rare, though.
+
+	Until a subsequent reboot, various running services will show up in
+	ps(1) output and /proc as owned by "postfix".  This is no problem.
+
 20170122:
 	MINIX 3 did not import NetBSD's passwd.conf file, which makes the
 	userland fall back by default to the old, broken UNIX password hashing