Add some wisdom to the jail setup instructions.

1 files changed, 11 insertions, 1 deletions

diff --git a/usr.sbin/jail/jail.8 b/usr.sbin/jail/jail.8
index f45ddf0cdb20..439677a8696e 100644
--- a/usr.sbin/jail/jail.8
+++ b/usr.sbin/jail/jail.8
@@ -52,10 +52,12 @@ Please see the
 man page for further details.
 .Sh EXAMPLES
 .Ss "Setting up a Jail Directory Tree"
-This shows how to setup a jail directory tree:
+This example shows how to setup a jail directory tree
+containing an entire FreeBSD distribution:
 .Bd -literal
 D=/here/is/the/jail
 cd /usr/src
+mkdir -p $D
 make world DESTDIR=$D
 cd etc
 make distribution DESTDIR=$D -DNO_MAKEDEV_RUN
@@ -64,6 +66,14 @@ sh MAKEDEV jail
 cd $D
 ln -sf dev/null kernel
 .Ed
+.Pp
+In many cases this example would put far more stuff in the jail than is needed.
+In the other extreme case a jail might contain only one singe file:
+the executable to be run in the jail.
+.Pp
+We recommend experimentation and caution that it is a lot easier to
+start with a ``fat'' jail and remove things until it stops working,
+than it is to start with a ``thin'' jail and add things until it works.
 .Ss "Setting Up a Jail"
 Do what was described in
 .Sx "Setting Up a Jail Directory Tree"