Nagios notification commands and Postfix sendmail

Postfix does not have a mail command. But this is used to send out notifications in the Nagios default configuration. Postfix installs its own sendmail command which works with a different syntax and is placed into a different directory. To tell Nagios that it should use sendmail open the commands.cfg file from Nagios and locate the following lines.

# 'notify-host-by-email' command definition
define command{
       command_name    notify-host-by-email
       command_line    /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HO
STADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /usr/bin/mail -s "** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **" $CONTACTEM
AIL$
       }

# 'notify-service-by-email' command definition
define command{
       command_name    notify-service-by-email
       command_line    /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddre
ss: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /usr/bin/mail -s "** $NOTIFICATIONTYPE$ Servi
ce Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
       }

These lines are used to send email notifications. Only two changes are needed to make them work with Postfix sendmail. The first one is to move the subject line after parameter (-s) to the beginning of the second string which follows printf. The second one is to change the path and command itself from /usr/bin/mail to /usr/sbin/sendmail. Here are the modified commands.

# NEW 'notify-host-by-email' command definition
define command{
        command_name    notify-host-by-email
        command_line    /usr/bin/printf "%b" "Subject:** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **\n***** Nagios *****\n\nNotification Type
: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /usr/sbin/sendmail $
CONTACTEMAIL$
        }

# NEW 'notify-service-by-email' command definition
define command{
        command_name    notify-service-by-email
        command_line    /usr/bin/printf "%b" "Subject:** $NOTIFICATIONTYPE$ Service Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **\n***** Nagios *****
\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATE
TIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /usr/sbin/sendmail $CONTACTEMAIL$

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