I am trying to reproduce that here: %> TZ=UTC ./check_http -v -p443 -H github.com -C 7,3 --sni OK - Certificate 'github.com' will expire on Tue 12 Apr 2016 12:00:00 PM UTC. %> ./check_http -v -p443 -H github.com -C 7,3 --sni OK - Certificate 'github.com' will expire on Tue 12 Apr 2016 01:00:00 PM CEST. %> TZ=Europe/Berlin ./check_http -v -p443 -H github.com -C 7,3 --sni OK - Certificate 'github.com' will expire on Tue 12 Apr 2016 01:00:00 PM CEST. %> ./check_http -V check_http v2.1.1.51.g08fc (monitoring-plugins 2.1.1) I'd say, the real question is, why is there no timezone mentioned in your output. The check uses strftime with "%c" fomat. This is "The preferred date and time representation for the current locale.". So, if i set LANG as well, i get close to your results: LANG=C TZ=Europe/Berlin ./check_http -v -p443 -H github.com -C 7,3 --sni OK - Certificate 'github.com' will expire on Tue Apr 12 13:00:00 2016. Which is not wrong, but you have to know the timezone :-) In the end, i would leave it like it is. With every ENV variable we set to a fixed value, we just trade reduced flexibility for a specific use case. — <a href="https://github.com/monitoring-plugins/monitoring-plugins/pull/1337#issuecomment-95487885">Reply to this email on GitHub</a>.<img alt="" height="1" src="https://github.com/notifications/beacon/AFQl2YsLGfvL5GISn8egiRi7uKEgponiks5oCKPvgaJpZM4EGE_1.gif" width="1" /> <div itemscope itemtype="http://schema.org/EmailMessage"> <div itemprop="action" itemscope itemtype="http://schema.org/ViewAction"> <link itemprop="url" href="https://github.com/monitoring-plugins/monitoring-plugins/pull/1337#issuecomment-95487885"></link> <meta itemprop="name" content="View Pull Request"></meta> </div> <meta itemprop="description" content="View this Pull Request on GitHub"></meta> </div>