Frequently Asked Questions about BIND 9 Q: Why doesn't -u work on Linux 2.2.x when I build with --enable-threads? 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 (the default) 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: If the Linux kernel is 2.4.7 or newer, multithreaded core dumps are usable (that is, the correct thread is dumped). Otherwise, if using a 2.2 kernel, apply the kernel patch found in contrib/linux/coredump-patch and rebuild the kernel. This patch will cause 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 { ; }; 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 is fixed in BIND 8.2.4. It can be safely ignored - the notify has been acted on by the slave despite the error message. Q: I keep getting log messages like the following. Why? Dec 4 23:47:59 client 10.0.0.1#1355: updating zone 'example.com/IN': update failed: 'RRset exists (value dependent)' prerequisite not satisfied (NXRRSET) A: DNS updates allow the update request to test to see if certain conditions are met prior to proceeding with the update. The message above is saying that conditions were not met and the update is not proceeding. See doc/rfc/rfc2136.txt for more details on prerequisites. Q: I keep getting log messages like the following. Why? Jun 21 12:00:00.000 client 10.0.0.1#1234: update denied A: Someone is trying to update your DNS data using the RFC2136 Dynamic Update protocol. Windows 2000 machines have a habit of sending dynamic update requests to DNS servers without being specifically configured to do so. If the update requests are coming from a Windows 2000 machine, see for information about how to turn them off. Q: I see a log message like the following. Why? couldn't open pid file '/var/run/named.pid': Permission denied A: You are most likely running named as a non-root user, and that user does not have permission to write in /var/run. The common ways of fixing this are to create a /var/run/named directory owned by the named user and set pid-file to "/var/run/named/named.pid", or set pid-file to "named.pid", which will put the file in the directory specified by the directory option (which, in this case, must be writable by the named user). Q: When I do a "dig . ns", many of the A records for the root servers are missing. Why? A: This is normal and harmless. It is a somewhat confusing side effect of the way BIND 9 does RFC2181 trust ranking and of the efforts BIND 9 makes to avoid promoting glue into answers. When BIND 9 first starts up and primes its cache, it receives the root server addresses as additional data in an authoritative response from a root server, and these records are eligible for inclusion as additional data in responses. Subsequently it receives a subset of the root server addresses as additional data in a non-authoritative (referral) response from a root server. This causes the addresses to now be considered non-authoritative (glue) data, which is not eligible for inclusion in responses. The server does have a complete set of root server addresses cached at all times, it just may not include all of them as additional data, depending on whether they were last received as answers or as glue. You can always look up the addresses with explicit queries like "dig a.root-servers.net A". Q: Zone transfers from my BIND 9 master to my Windows 2000 slave fail. Why? A: This may be caused by a bug in the Windows 2000 DNS server where DNS messages larger than 16K are not handled properly. This can be worked around by setting the option "transfer-format one-answer;". Also check whether your zone contains domain names with embedded spaces or other special characters, like "John\032Doe\213s\032Computer", since such names have been known to cause Windows 2000 slaves to incorrectly reject the zone. Q: Why don't my zones reload when I do an "rndc reload" or SIGHUP? A: A zone can be updated either by editing zone files and reloading the server or by dynamic update, but not both. If you have enabled dynamic update for a zone using the "allow-update" option, you are not supposed to edit the zone file by hand, and the server will not attempt to reload it. Q: I can query the nameserver from the nameserver but not from other machines. Why? A: This is usually the result of the firewall configuration stopping the queries and / or the replies. Q: How can I make a server a slave for both an internal and an external view at the same time? When I tried, both views on the slave were transferred from the same view on the master. A: You will need to give the master and slave multiple IP addresses and use those to make sure you reach the correct view on the other machine. e.g. Master: 10.0.1.1 (internal), 10.0.1.2 (external, IP alias) internal: match-clients { !10.0.1.2; !10.0.1.4; 10.0.1/24; }; notify-source 10.0.1.1; transfer-source 10.0.1.1; query-source address 10.0.1.1; external: match-clients { any; }; recursion no; // don't offer recursion to the world notify-source 10.0.1.2; transfer-source 10.0.1.2; query-source address 10.0.1.2; Slave: 10.0.1.3 (internal), 10.0.1.4 (external, IP alias) internal: match-clients { !10.0.1.2; !10.0.1.4; 10.0.1/24; }; notify-source 10.0.1.3; transfer-source 10.0.1.3; query-source address 10.0.1.3; external: match-clients { any; }; recursion no; // don't offer recursion to the world notify-source 10.0.1.4; transfer-source 10.0.1.4; query-source address 10.0.1.4; You put the external address on the alias so that all the other dns clients on these boxes see the internal view by default. Q: When I try to use rndc, I get the error message "network unreachable" or "connection refused", even though I know named is running. A: You probably have "default-server localhost" in /etc/rndc.conf, your /etc/hosts or DNS maps "localhost" to both the IPv4 loopback address 127.0.0.1 and the IPv6 loopback address ::1, and you do not have IPv6 fully operational. Change the "default-server localhost" to "default-server 127.0.0.1" to make sure rdnc does not try to contact the name server using IPv6. Q: I have Freebsd 4.4 and "rndc-confgen -a" just sits there. A: /dev/random is not configured. Use rndcontrol(8) to tell the kernel to use certain interrupts as a source of random events. You can make this permanent by setting rand_irqs in /etc/rc.conf. e.g. /etc/rc.conf rand_irqs="3 14 15" Q: Why is named listening on UDP port other than 53? A: Named uses a system selected port to make queries of other nameservers. This behaviour can be overridden by using query-source to lock down the port and/or address. Q: I get error messages like "multiple RRs of singleton type" and "CNAME and other data" when transferring a zone. What does this mean? A: These indicate a malformed master zone. You can identify the exact records involved by transferring the zone using dig then running named-checkzone on it. e.g. dig axfr example.com @master-server > tmp named-checkzone example.com tmp Q: I get error messages like "named.conf:99: unexpected end of input" where 99 is the last line of named.conf. A: Some text editors (notepad and wordpad) fail to put a line termination indication (e.g. CR/LF) on the last line of a text file. This can be fixed by "adding" a blank line to the end of the file. Named expects to see EOF immediately after EOL and treats text files where this is not met as truncated. Q: I get warning messages like "zone example.com/IN: refresh: failure trying master 1.2.3.4#53: timed out". A: Check that you can make UDP queries from the slave to the master dig +norec example.com soa @1.2.3.4 A: You could be generating queries faster than the slave can cope with. Lower the serial query rate. serial-query-rate 5; // default 20