UPDATE: I just had a server experience downtime due to this bug. An update of the apache2 package was automatically triggered on a client's 16.04 LTS server on Aug 31 via the unattended-upgrades cron script, and apparently before this update, the last time the Apache service had been restarted was done via "apachectl graceful", without an appropriately modified /usr/sbin/apachectl as described in my initial report, so the usual unattended-upgrades stop-and-start which follows an Apache update failed to perform as expected, leaving the service in the stopped state.
Therefore, it appears there is now a definite case where a user invoking "apachectl graceful" leads to downtime. To mitigate this, you can either disable/uninstall unattended-upgrades, or patch the /usr/sbin/apachectl file as described in this bug report.
I have deleted the old patch file and replaced it with an actual correct one based on the apache2ctl file on my client's server after the latest apache2 package update, now that I know how diff patch files are generated
UPDATE: I just had a server experience downtime due to this bug. An update of the apache2 package was automatically triggered on a client's 16.04 LTS server on Aug 31 via the unattended-upgrades cron script, and apparently before this update, the last time the Apache service had been restarted was done via "apachectl graceful", without an appropriately modified /usr/sbin/apachectl as described in my initial report, so the usual unattended-upgrades stop-and-start which follows an Apache update failed to perform as expected, leaving the service in the stopped state.
Therefore, it appears there is now a definite case where a user invoking "apachectl graceful" leads to downtime. To mitigate this, you can either disable/uninstall unattended- upgrades, or patch the /usr/sbin/apachectl file as described in this bug report.
I have deleted the old patch file and replaced it with an actual correct one based on the apache2ctl file on my client's server after the latest apache2 package update, now that I know how diff patch files are generated