namedをchrootで動かしている時は、dfのバグでこうなるようです。
https://bugzilla.redhat.com/show_bug.cgi?id=836557

# du -hs
du: WARNING: Circular directory structure.
This almost certainly means that you have a corrupted file system.
NOTIFY YOUR SYSTEM MANAGER.
The following directory is part of the cycle:
  `./named/chroot/var/named' 

■chrootのnamedが動いている場合

# /etc/init.d/named status
version: 9.7.3-P3-RedHat-9.7.3-8.P3.el6_2.2 (none)
CPUs found: 1
worker threads: 1
number of zones: 17
debug level: 0
xfers running: 0
xfers deferred: 0
soa queries in progress: 0
query logging is OFF
recursive clients: 0/0/1000
tcp clients: 0/100
server is up and running
named (pid  2017) is running...
# du -hs
du: WARNING: Circular directory structure.
This almost certainly means that you have a corrupted file system.
NOTIFY YOUR SYSTEM MANAGER.
The following directory is part of the cycle:
  `./named/chroot/var/named'

535M    .

■chrootのnamedが動いていない場合

# /etc/init.d/named status
rndc: connect failed: 127.0.0.1#953: connection refused
named is stopped
# du -hs
535M    .