The active ABS log file abs.log is located in the logs directory and rotated every 24-hours at midnight local time. The rotated log files append timestamps to the name and follow the naming convention of abs.log.<yyyy>-<mm>-<dd> (for example, abs.log.2018-11-24). Here is an example:

-rw-r--r--. 1 root root 68K Apr 25 23:59 abs.log.2019-04-25
-rw-r--r--. 1 root root 68K Apr 25 23:59 abs.log.2019-04-24
-rw-r--r--. 1 root root 68K Apr 26 23:59 abs.log.2018-04-26
-rw-r--r--. 1 root root 158K Apr 27 23:59 abs.log.2018-04-27
-rw-r--r--. 1 root root 32K Apr 28 11:21 abs.log

The ABS log file contains INFO messages (for example, ABS started, MongoDB status) and ERROR messages (for example, MongoDB is not reachable). The log files also contains entry of all the email alerts sent. Here is a snippet of an abs.log file:

2019-04-28 11:16:45 INFO - starting abs periodic actions
2019-04-28 11:16:45 INFO - MongoDB heartbeat success
2019-04-28 11:16:45 INFO - notification node not set.
2019-04-28 11:16:45 INFO - training period 1 hours.
2019-04-28 11:16:45 INFO - system threshold update interval 1 hour(s).
2019-04-28 11:16:45 INFO - api discovery interval 1 hour(s).
2019-04-28 11:16:45 INFO - subpath limit: 100
2019-04-28 11:16:45 INFO - ABS started successfully...
2019-04-28 11:17:45 INFO - MongoDB heartbeat success
2019-04-28 11:19:45 ERROR - MongoDB heartbeat failure