check_ping behaves different between EL8 (working) and EL9 (IPv6 broken)

[pbiering]

While migrating monitoring system from EL8 to EL9 a strange issue was found:

• EL9 check_ping from RPM has a problem, option -6 is not proper honored and ping is called with -4

rpm -qf /opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping
omd-5.20-labs-edition-el9-1.x86_64

/opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping -V
check_ping v2.3.3 (monitoring-plugins 2.3.3)

/opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping -H ipv6.bieringer.de -w 3000.0,80% -c 5000.0,100% -p 5 -6
/usr/sbin/ping -4 -n -U -w 30 -c 5 ipv6.bieringer.de
CRITICAL - Could not interpret output from ping command

• EL8 check_ping from RPM is ok

rpm -qf /opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping
omd-5.20-labs-edition-el8-1.x86_64

/opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping -V
check_ping v2.3.3 (monitoring-plugins 2.3.3)

/opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping -H ipv6.bieringer.de -w 3000.0,80% -c 5000.0,100% -p 5 -6
PING OK - Packet loss = 0%, RTA = 12.23 ms|rta=12.230000ms;3000.000000;5000.000000;0.000000 pl=0%;80;100;0;

BTW: copy of binary check_ping from EL8 to EL9 would be a workaround as it is running even on next major version.

[pbiering]

found even more curious behavior while tweaking local DNS resolution:

/opt/omd/versions/5.20-labs-edition/lib/monitoring-plugins/check_ping -H ipv6.bieringer.de -w 3000.0,80% -c 5000.0,100% -p 5 -6
/usr/sbin/ping -4 -n -U -w 30 -c 5 ipv6.bieringer.de
PING OK - Packet loss = 0%, RTA = 0.12 ms|rta=0.119000ms;3000.000000;5000.000000;0.000000 pl=0%;80;100;0;
/usr/sbin/ping: ipv6.bieringer.de: Address family for hostname not supported

does it try IPv4 ping even in case of -6 is supplied?

[sni]

you can always add -vvv to see the actual ping command executed.

[pbiering]

The issue still persists on 5.30 and EL9:

opt/omd/versions/5.30-labs-edition/lib/monitoring-plugins/check_ping -h
check_ping v2.3.5 (monitoring-plugins 2.3.5)
...
Usage:
check_ping -H <host_address> -w <wrta>,<wpl>% -c <crta>,<cpl>%
 [-p packets] [-t timeout] [-4|-6]
...
 -4, --use-ipv4
    Use IPv4 connection
 -6, --use-ipv6
    Use IPv6 connection
...

Result is that -6 is not honored and -4 is selected

/opt/omd/versions/5.30-labs-edition/lib/monitoring-plugins/check_ping -H ftp6.bieringer.de -w 3000.0,80% -c 5000.0,100% -p 5 -6
/usr/sbin/ping -4 -n -U -w 30 -c 5 ftp6.bieringer.de
CRITICAL - Could not interpret output from ping command
```