This patch is useful for certain jail environments that
   meet the following criteria:

    - /etc is mounted read-only.
    - The passwd files are symlinked to a different
      directory which is root-writable.
    - Users shall be able to use passwd(1), chsh(1) etc.

   Ordinarily that won't work because the tools that
   work on the passwd files try to create temporary files
   in /etc.  That fails because /etc is read-only.

   This patch changes the way temporary files are created
   by first calling realpath(3) on the symlink, so it is
   resolved to the directory containing the actual passwd
   files, which is root-writable.  Any temporary files
   are then created in that directory.

   How to use:

   Make sure your source (/usr/src) is up to date.  Please
   download the patch appropriate for your FreeBSD version.
   The patch is relative to /usr/src, so the following
   commands should work:

   # cd /usr/src
   # patch < /tmp/X-stable.patch.txt

   Then perform the usual "make world" update, please see
   the FreeBSD Handbook and /usr/src/UPDATING for details.
   You're done.

   If you have already done a "buildworld" before applying
   the patch, and you don't want to build everything all
   over again, then perform the following steps.

   On FreeBSD 4 you need to rebuild and install the tools
   vipw (src/usr.sbin/vipw), chpass (src/usr.bin/chpass)
   and passwd (src/usr.bin/passwd).
   On FreeBSD 5 and above you only need to rebuild and
   install libutil (src/lib/libutil).

   To rebuild and install, go to the source directory (the
   one given in parentheses above), then do this:

   # make clean
   # make
   # make install   # Unless you do "installworld" anyway!

   This assumes that you have done a "buildworld" before
   and have a populated /usr/obj directory.

--