Frequently Asked Questions about BIND 9


Q: Why doesn't -u work on Linux 2.2.x?

A: Linux threads do not fully implement the Posix threads (pthreads) standard.
In particular, setuid() operates only on the current thread, not the full
process.  Because of this limitation, BIND 9 cannot use setuid() on Linux as it
can on all other supported platforms.  setuid() cannot be called before
creating threads, since the server does not start listening on reserved ports
until after threads have started.

  In the 2.3.99-pre3 and newer kernels, the ability to preserve capabilities
across a setuid() call is present.  This allows BIND 9 to call setuid() early,
while retaining the ability to bind reserved ports.  This is a Linux-specific
hack.

  On a 2.2 kernel, BIND 9 does drop many root privileges, so it should be less
of a security risk than a root process that has not dropped privileges.

  If Linux threads ever work correctly, this restriction will go away.

  Configuring BIND9 with the --disable-threads option causes a non-threaded
version to be built, which will allow -u to be used.


Q: Why does named log the error message "no TTL specified" and refuse
to load my zone file?

A: Your zone file must either have a line like

   $TTL 86400

at the beginning, or the first record in it must have a TTL field,
like the "84600" in this example:

   example.com. 86400 IN SOA ns hostmaster ( 1 3600 1800 1814400 3600 )

BIND 8 incorrectly accepted files that had neither.


Q: Why do I see 5 (or more) copies of named on Linux?

A: Linux threads each show up as a process under ps.  The approximate
number of threads running is n+4, where n is the number of CPUs.


Q: Why does BIND 9 log "permission denied" errors accessing its
configuration files on my Linux sysetm even though it is running as
root?

A: On Linux, BIND 9 drops most of its root privileges on startup.
This including the privilege to open files owned by other users.
Therefore, if the server is running as root, the configuration files
should also be owned by root.