12.2.1 Debugging Command-Line Option

When troubleshooting, you sometimes need to see the sort list, know which interface a file descriptor is bound to, or find out where in the initialization stage the name server was when it exited (if the syslog error message wasn't clear enough). To see this kind of debugging information, you'll have to start debugging with a command-line option; by the time you send a signal, it will be too late. The command-line option for debugging is -d level . When you use the command-line option to turn on debugging, a BIND 4 name server will not go into the background as it does normally; you'll have to add the "&" at the end of your command line to get your shell prompt back. Here's how to start the name server at debugging level 1:

# 

/etc/named -d 1 &

12.2.2 Changing the Debugging Level with Signals

If you don't need to see the name server initialization, start your name server without the debugging command-line option. You can later turn debugging on and off by sending the USR 1 and USR 2 signals to the name server process. The first USR 1 signal causes named to start writing debugging output at level 1. Each subsequent USR 1 signal increases the debugging level by 1. Send USR 2 to turn off debugging. Here, we set debugging to level 3, then turn debugging off:

# 

kill -USR1 `cat /etc/named.pid`

       
 - Level 1

# 

kill -USR1 `cat /etc/named.pid`

       
 - Level 2

# 

kill -USR1 `cat /etc/named.pid`

       
 - Level 3

# 

kill -USR2 `cat /etc/named.pid`

       
 - Off

And, as you might expect, if you turn on debugging from the command line, you can still send USR 1 and USR 2 signals to the name server.