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 2.2.18 or 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 warning message "no TTL specified - using SOA

MINTTL instead"?

A: Your zone file is illegal according to RFC1035. It 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 )

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. Note that

the amount of memory used is not cumulative; if each process is using 10M of

memory, only a total of 10M is used.

Q: Why does BIND 9 log "permission denied" errors accessing its

configuration files or zones on my Linux system 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

and zone files should also be owned by root.

Q: Why do I get errors like "dns_zone_load: zone foo/IN: loading master file

bar: ran out of space"

A: This is often caused by TXT records with missing close quotes. Check that

all TXT records containing quoted strings have both open and close quotes.

Q: How do I produce a usable core file from a multithreaded named

on Linux?

A: Apply the kernel patch found in bind9/linux/coredump-patch and rebuild

the kernel. This patch causes multithreaded programs to dump the correct

thread.

Q: How do I restrict people from looking up the server version?

A: Put a "version" option containing something other than the real

version in the "options" section of named.conf. Note doing this will

not prevent attacks and may impede people trying to diagnose problems

with your server. Also it is possible to "fingerprint" nameservers to

determine their version.

Q: How do I restrict only remote users from looking up the server

version?

A: The following view statement will intercept lookups as the internal

view that holds the version information will be matched last. The

caveats of the previous answer still apply, of course.

view "chaos" chaos {

match-clients { <those to be refused>; };

allow-query { none; };

zone "." {

type hint;

file "/dev/null"; // or any empty file

};

};

Q: What do "no source of entropy found" or "could not open entropy source foo"

mean?

A: The server requires a source of entropy to perform certain operations,

mostly DNSSEC related. These messages indicate that you have no source

of entropy. On systems with /dev/random or an equivalent, it is used by

default. A source of entropy can also be defined using the random-device

option in named.conf.

Q: I installed BIND 9 and restarted named, but it's still BIND 8. Why?

A: BIND 9 is installed under /usr/local by default. BIND 8 is often

installed under /usr. Check that the correct named is running.

Q: I'm trying to use TSIG to authenticate dynamic updates or zone

transfers. I'm sure I have the keys set up correctly, but the server

is rejecting the TSIG. Why?

A: This may be a clock skew problem. Check that the the clocks on

the client and server are properly synchronized (e.g., using ntp).

Q: I'm trying to compile BIND 9, and "make" is failing due to files not

being found. Why?

A: Using a parallel or distributed "make" to build BIND 9 is not

supported, and doesn't work. If you are using one of these, use

normal make or gmake instead.

Q: I have a BIND 9 master and a BIND 8.2.3 slave, and the master is

logging error messages like "notify to 10.0.0.1#53 failed: unexpected

end of input". What's wrong?

A: This error message is caused by a known bug in BIND 8.2.3 and will

be fixed in 8.2.4. It can be safely ignored - the notify has been

acted on by the slave despite the error message.