It can be really useful to monitor, if you need to exchange any ssl certificates.
Here is a short script which enables you to do that.
#!/bin/bash
# check if target was provided
if [ -z "$1" ]; then
echo "no target provided"
exit 1
fi
# set target port to second argument
TargetPort=$2
# check if a second argument was provided. if not set default port.
if [ -z "$2" ]; then
TargetPort=443
fi
# openssl does not return so pipe the `echo -n` to close it once it finishes
# use openssl s_client to fetch the certificate from the target
# and use openssl x509 to extract the dates from the certificate.
# Then grep for the expiration date with `notAfter=` and remove "notAfter" from the output.
# You are left with the expiration date in a pretty formating.
ExpDatePretty=$(echo -n | openssl s_client -connect $1:$TargetPort 2> /dev/null | openssl x509 -text -noout -dates | grep notAfter= | sed 's/notAfter=//')
# convert the pretty timestamp to unix epoch timestamp
ExpDateEpoch=$(date --date="$ExpDatePretty" +%s)
# get the current date as unix epoch timestamp
CurDateEpoch=$(date +%s)
# get the difference in seconds between current date and expiration date
RemainingSeconds=$(($ExpDateEpoch-$CurDateEpoch))
RemainingDays=$(($RemainingSeconds/60/60/24))
echo "$RemainingDays days remaining."
# Less then 10 days, return status WARNING
if [[ $RemainingDays -lt 10 ]]; then
exit 2
# Less than 30 days, return status CRITICAL
elif [[ $RemainingDays -lt 30 ]]; then
exit 1
# Return status OK
else
exit 0
fi
To use it, we need to create a command and a service. This can be done in any config file in your nagios-configuration-directory.
define command {
command_name check_cert_valid_time
command_line $USER1$/check_cert_valid_time.sh $ARG1$ $ARG2$
}
define service {
service_description Expire Certificate nagios-01.home
use local-service
host_name nagios-01.home
check_command check_cert_valid_time!nagios-01.home!443
}
Last we need to reload nagios, to load the new configuration changes.
$ systemctl reload nagios
Now you have certificate check for the host nagios-01.home. Of course you will need to adjust this name to your hostname.
