ISC-dhcpd with newsyslog

Problem

Problem: my DHCP server crashed every few days.

Analysis

A quick look at the log file gave a hint that the crash occured just when newsyslog was rotating the log files:

Feb 15 02:59:46 wolfje dhcpd: DHCPACK on 172.25.129.98 to 00:26:4a:e8:ab:b9 via em3
Feb 15 03:00:00 wolfje newsyslog[92690]: logfile turned over due to size>100K
Feb 15 09:02:45 wolfje dhcpd: Internet Systems Consortium DHCP Server 4.2.3-P2
... further boot log of ISC-dhcpd ...

Feb 20 13:59:39 dhcpd: DHCPREQUEST for 172.25.129.67 from 00:13:d3:a2:57:59 via em3
Feb 20 13:59:39 dhcpd: DHCPACK on 172.25.129.67 to 00:13:d3:a2:57:59 via em3
Feb 20 14:00:00 newsyslog[14620]: logfile turned over due to size>100K
Feb 20 15:30:24 dhcpd: Internet Systems Consortium DHCP Server 4.2.3-P2
Feb 20 15:30:24 dhcpd: Copyright 2004-2012 Internet Systems Consortium.
Feb 20 15:30:24 dhcpd: All rights reserved.
... further boot log of ISC-dhcpd ...

Now I recently added the following line to /etc/newsyslog.conf:

/var/log/dhcpd.log	dhcpd:audit	640  10	   100	*     C	/var/run/dhcpd/dhcpd.pid 

The PID file means that newsyslog will send a SIGHUP to the process ID (PID) of dhcpd when it is rotated.

From the DHCP FAQ:

How do you have dhcpd reload its configuration file?

At this time, the dhcpd server doesn't have any reload mechanism. It doesn't handle HUP signal nor have a 'soft' reconfiguration method. The server has to be stopped and restarted.

So this SIGHUP caused the DHCP server to stop.

Solution

My /etc/newsyslog.conf configuration was at fault. It was easily solved by using syslog, and sending a SIGHUP to syslog instead of dhcpd:

From /usr/local/etc/dhcpd.conf:

# Log to syslog
log-facility local7;

And in /etc/newsyslog.conf:

/var/log/dhcpd.log	dhcpd:audit	640  10	   10	*     C