Monitoring SSL Certificate Expiration with Zabbix

If you run some websites/webservices that run over HTTPS, you might be interested in getting some notice before your SSL Certificate is about to expire. If you already use Zabbix, here is a possible way to do so.

Place this script somewhere accessible for the “zabbix” agent-user on the system to monitor:


# 2012, Looke

# Checks whether a SSL x509 Certificate expires within a specified amount of seconds.
# Takes two arguments: 
# 1. Certificate
# 2. Time Until Expiration in Seconds


if [ -f "$1" ] && [ "$(file -b $1)" == "PEM certificate" ] && [ -n $2 ] && [ $2 -eq $2 2> /dev/null ]
        $OPENSSL x509 -noout -checkend $2 -in $1
        if [ $? -gt 0 ]
                echo 1
                echo 0

Unfortunately there is no way to check the returncode of the command/script in Zabbix, so we have to echo our return value (0 for certificate doesn’t expire within the specified amount of seconds, 1 for certificate does expire).

Also, make sure you have allowed the execution of remote commands in zabbix_agentd.conf:


Here is how you setup the check in Zabbix:

Zabbix Item – Checking if a certificate expires within 30 days (2592000 seconds)
Type: Zabbix agent
Key:[/home/zabbix/bin/ /var/www/ 2592000]
Type of information: Numeric (unsigned)
Data Type: Decimal

Now, add a Trigger based on this Item and you’re ready to go.

More info

Sending Zabbix Alert SMS via USB modem

During some Zabbix sessions, I thought it would be nice to be able to alert via SMS. Zabbix, out of the box, supports the possibility to send SMS via attached GSM modems, so I gave it a try. I am currently using a Huawei USB modem:

Bus 003 Device 011: ID 12d1:1003 Huawei Technologies Co., Ltd. E220 HSDPA Modem / E230/E270/E870 HSDPA/HSUPA Modem

Unfortunately, this modem has some troubles with the AT command sequences Zabbix sends:

   856:20120120:170920.965 Read from GSM modem [^MOK^M]
   856:20120120:170920.965 End of read_gsm():SUCCEED
   856:20120120:170920.965 Write to GSM modem [ATE0^M]
   856:20120120:170920.965 In read_gsm() [OK] [NULL] [NULL] [NULL]
   856:20120120:170921.069 Read from GSM modem [^MOK^M]
   856:20120120:170921.069 In check_modem_result()
   856:20120120:170921.069 End of check_modem_result():SUCCEED
   856:20120120:170921.069 End of read_gsm():SUCCEED
   856:20120120:170921.069 Write to GSM modem [AT^M]
   856:20120120:170921.069 In read_gsm() [OK] [NULL] [NULL] [NULL]
   856:20120120:170921.173 Read from GSM modem [^MOK^M]
   856:20120120:170921.174 In check_modem_result()
   856:20120120:170921.174 End of check_modem_result():SUCCEED
   856:20120120:170921.174 End of read_gsm():SUCCEED
   856:20120120:170921.174 Write to GSM modem [AT+CMGF=1^M]
   856:20120120:170921.174 In read_gsm() [OK] [NULL] [NULL] [NULL]
   856:20120120:170921.277 Read from GSM modem [^MOK^M]
   856:20120120:170921.277 In check_modem_result()
   856:20120120:170921.277 End of check_modem_result():SUCCEED
   856:20120120:170921.277 End of read_gsm():SUCCEED
   856:20120120:170921.277 Write to GSM modem [AT+CMGS="]
   856:20120120:170921.277 Write to GSM modem [0041791234567]
   856:20120120:170921.277 Write to GSM modem ["^M]
   856:20120120:170921.277 In read_gsm() [> ] [NULL] [NULL] [NULL]
   856:20120120:170921.385 Read from GSM modem [^M> ]
   856:20120120:170921.385 In check_modem_result()
   856:20120120:170921.385 End of check_modem_result():SUCCEED
   856:20120120:170921.385 End of read_gsm():SUCCEED
   856:20120120:170921.385 Write to GSM modem [Host xyz is unreachable: PROBLEM]
   856:20120120:170921.385 Write to GSM modem [^Z]
   856:20120120:170921.385 In read_gsm() [+CMGS: ] [NULL] [NULL] [NULL]
   856:20120120:170921.489 Read from GSM modem [^M]
   856:20120120:170921.489 In check_modem_result()
   856:20120120:170921.489 End of check_modem_result():FAIL
   856:20120120:170921.489 End of read_gsm():FAIL
   856:20120120:170921.489 Write to GSM modem [^MESC^Z]
   856:20120120:170921.489 In read_gsm() [] [NULL] [NULL] [NULL]
   856:20120120:170921.489 Error during wait for GSM modem.
   856:20120120:170921.489 Read from GSM modem []
   856:20120120:170921.489 End of read_gsm():SUCCEED
   856:20120120:170921.494 End of send_sms():FAIL
   856:20120120:170921.494 End execute_action()
   856:20120120:170921.494 Error sending alert ID [62]

After some research I figured out that it probably would be a better idea to write a wrapper-script to implement the SMS functionality. There is actually a way to fix this AT command sequence issue, but it would require recompiling some parts of Zabbix (which is not an option for me, as I use the Debian packaged Zabbix). To interface with the modem, I am finally using Gnokii:


port = /dev/ttyUSB1
model = AT
connection = serial

Thats the script I use to send the alerts to (taken straight from


echo "To: '$1' Text: '$3'" >> ${LOGFILE} 
PHONENR=`echo "$1" | sed s#\s##` 
/bin/echo "$3" | /usr/bin/gnokii --config /etc/zabbix/gnokii.conf --sendsms "${PHONENR}" 1>>${LOGFILE} 2>&1

Here are some screenshots on how to configure the SMS alert in the Zabbix GUI:


Monitoring ESX servers with Zabbix

Install the Zabbix monitoring agent binaries
Installing the Zabbix agent is quite simple, you could try the RedHat RPMs… I tried with the generic Linux 2.6.x binaries and it worked.
The only thing you have to consider, that the ESX console doesn’t come with wget, so you probably will have to SCP the rpm package to your ESX server.

Create a Firewall rule for the in- and outbound monitoring ports used by Zabbix
There are two ways of doing that:

  1. Issuing the following commands on the ESX command console – nice, but annoying for more that two ESXes:
    esxcfg-firewall -openPort 10050,tcp,in,zabbixClient
    esxcfg-firewall -openPort 10051,tcp,out,zabbixServer
  2. Or creating a XML file which holds the definition of the rule, which later allows more convenient handling (activating or deactivating) of the rule through the vSphere Client GUI – neat for larger farms of ESX servers.

Here is what you need to do to implement the second option (works for ESX 4):

  • Connect to the ESX console and create a new XML file in /etc/vmware/firewall called zabbixMonitoring.xml
  • Contents of /etc/vmware/firewall/zabbixMonitoring.xml:
    <!-- Firewall configuration information for Zabbix Monitoring system -->
     <rule id='0000'>
     <port type='dst'>10050</port>
     <flags>-m state --state NEW</flags>
     <rule id='0001'>
     <port type='dst'>10051</port>
     <flags>-m state --state NEW</flags>
  • Restart the VMware management service: service mgmt-vmware restart
  • Connect to the ESX server and enable the Zabbix Monitoring rule in the vSphere Client GUI