I have set "$logLevel='7';" and "$paramDebugMode='true';" in files/config/parameters.php , so here is some additional information about my cron problem. In all these tests I have left my main browser (Firefox) open with an SSO-user that has administration rights continuously logged in. I also had a different make of browser (MS Edge) open and used that for logging in & out a non-SSO user that has administration rights (actually the inbuilt user #1) as a test to see if it restarted the dead cron process.
Pressing the cron run button on the Administration page generates log entries::
2019-08-13 00:38:45.969 ..... SCRIPT .... [IP redacted] =====/projects/tool/cronRun.php
2019-08-13 00:38:45.979 ..... SCRIPT .... [IP redacted] Page=cronRun.php
2019-08-13 00:38:45.979 ..... SCRIPT .... [IP redacted] refreshParameters()
2019-08-13 00:38:45.987 ..... SCRIPT .... [IP redacted] getProfile(objectOrIdProject=Audit #62)
2019-08-13 00:38:45.987 ..... SCRIPT .... [IP redacted] getProfile(objectOrIdProject=Audit #62)
2019-08-13 00:38:46.011 ===== TRACE ===== Cron started at 13/08/2019 00:38:46
There does not appear to be anything logged when the process is killed approx 20mins later. files/cron/RUNNING continues to exist, in this case with a last modified time of 00:55:06.
Logging in as a non-SSO user from the other make of browser generates log entries:
2019-08-13 02:13:48.513 ..... SCRIPT .... [IP redacted] Page=cronRelaunch.php
2019-08-13 02:13:48.514 ..... SCRIPT .... [IP redacted] refreshParameters()
2019-08-13 02:13:48.524 ..... SCRIPT .... [IP redacted] getProfile(objectOrIdProject=Audit #63)
2019-08-13 02:13:48.524 ..... SCRIPT .... [IP redacted] getProfile(objectOrIdProject=Audit #63)
2019-08-13 02:13:48.534 ===== TRACE ===== Cron started at 13/08/2019 02:13:48
files/cron/RUNNING get updated accordingly and the Administration page reports cron is running again.
Logging the non-SSO user out of the other browser and rebooting the server a short time later to apply a kernel patch does not remove files/cron/RUNNING but subsequently checking the Administration page does delete RUNNING. The page reports cron is stopped and there is nothing in the log file that refers to this or cron in general.
Logging in again from that other make of browser generates log entries:
2019-08-13 02:37:39.127 ..... SCRIPT .... [IP redacted] =====/projects/tool/cronRelaunch.php
2019-08-13 02:37:39.132 ..... SCRIPT .... [IP redacted] Page=cronRelaunch.php
2019-08-13 02:37:39.132 ..... SCRIPT .... [IP redacted] refreshParameters()
2019-08-13 02:37:39.141 ..... SCRIPT .... [IP redacted] getProfile(objectOrIdProject=Audit #65)
2019-08-13 02:37:39.142 ..... SCRIPT .... [IP redacted] getProfile(objectOrIdProject=Audit #65)
Note that there was no "===== TRACE ===== Cron started" entry at this point, and refreshing the Administration page reports cron as stopped.