The program has two modes of operation: normal mode and quiet mode. In normal mode, the certificate given by the filename argument is examined, and a warning email is issued to standard output if the certificate is outside its validity period, or approaching expiry. If the certificate cannot be found, or any errors occur whilst parsing the certificate, the certificate is ignored and no output is produced. In quiet mode, no output is given, but the exit status can still be used.
The exit code indicates the state of the certificate:
The certwatch program is run daily by crond from the file /etc/cron.daily/certwatch to warn about the imminent expiry of SSL certificates configured for use in the Apache HTTP server. This warning can be disabled by adding the line: NOCERTWATCH=yes to the file /etc/sysconfig/httpd. Options to pass to certwatch can be specified in that file in the CERTWATCH_OPTS environment variable.
/etc/cron.daily/certwatch
genkey(1)