Hi all, I am having trouble tracking down a bug in my monitoring setup. It all happened when I upgraded the monitored host (host B in my example below) to bullseye. Note that Host A is also running bullseye, but the problem didn't show itself until Host B was upgraded.
Here is the setup: Host A (monitoring): Installed: nagios4, nrpe-ng IP address: 192.0.2.1 Host B (monitored): Installed: nrpe-ng, monitoring-plugins-standard, bind9-dnsutils IP address: 192.0.2.2 Host C (monitored through host B): Installed: bind9 IP address: 192.0.2.3 Configured to answer authoritatively for example.com on port 53. nrpe over HTTPs DNS Host A ------------------> Host B -------------> Host C On Host B, I run the following: sudo /usr/bin/python3 /usr/sbin/nrpe-ng --debug -f --config /etc/nagios/nrpe-ng.cfg While that is running, I run the following on Host A: /usr/lib/nagios/plugins/check_nrpe_ng -H 192.0.2.2 -c check_dns -a example.com 192.0.2.3 0.1 1.0 The result of running the command on Host A is: DNS CRITICAL - '/usr/bin/nslookup -sil' msg parsing exited with no address On Host B, I see the following debug output: 200 POST /v1/check/check_dns (192.0.2.1) 78.05ms Executing: /usr/lib/nagios/plugins/check_dns -H example.com -s 192.0.2.3 -A -w 0.1 -c 1.0 When I run this exact command on Host B, I get: $ /usr/lib/nagios/plugins/check_dns -H example.com -s 192.0.2.3 -A -w 0.1 -c 1.0 DNS OK: 0.070 seconds response time. example.com returns 192.0.2.10,2001:db8::10|time=0.069825s;0.100000;1.000000;0.000000 Looks good! When I run nslookup (run by check_dns), it looks good too: $ /usr/bin/nslookup -sil example.com 192.0.2.3 Server: 192.0.2.3 Address: 192.0.2.3#53 Name: example.com Address: 192.0.2.10 Name: example.com Address: 2001:db8::10 After rerunning nrpe-ng with strace -f, I see something: [pid 1183842] write(2, "nslookup: ./src/unix/core.c:570:"..., 83) = 83 ... [pid 1183841] read(4, "nslookup: ./src/unix/core.c:570:"..., 4096) = 83 So it appears that the nslookup process is reporting an error. But I cannot reproduce it outside of nrpe-ng. Any suggestions? Casey