Where do weewx log files go?

[Bradley Dawson]

I have weewx installed on a RPi 3 and successfully collecting data from my weather station. I now want to use mqtt to send this data back to my server, so I have installed the mqtt extension as per instructions at https://github.com/weewx/weewx/wiki/mqtt. It all looks to have installed correctly (apart from the cjson library, but it says this is optional anyway) with appropriate changes made to the weewx.conf file. I modified this file to put my mqtt server address into it, but I am seeing nothing come out of it. I ran another program on the RPi which outputs  data to the same mqtt server and this works fine. 

I enabled the debug option in weewx.conf to see what is going on, but all I see in the syslog file is the few lines below. Is it trying to write to the exim4/mainlog file? 

Initially syslog was not installed and it didn't seem to want to install, so I tried syslog-ng, which installed and seems to be working. Do I need to point weewx logs into this somehow?

Jul  6 13:52:32 0000000028e33d47 systemd[1]: Starting LSB: weewx weather system...

Jul  6 13:52:33 0000000028e33d47 weewx[4086]: Starting weewx weather system: weewx.

Jul  6 13:52:33 0000000028e33d47 systemd[1]: Started LSB: weewx weather system.

Jul  6 13:53:17 0000000028e33d47 wpa_supplicant[557]: wlan0: WPA: Group rekeying completed with 78:8a:20:81:1b:52 [GTK=CCMP]

Jul  6 14:00:02 0000000028e33d47 cron[690]: 2020-07-06 14:00:02 1jsIlW-000157-2d Cannot open main log file "/var/log/exim4/mainlog": Permission denied: euid=109 egid=115

Jul  6 14:00:02 0000000028e33d47 cron[690]: 2020-07-06 14:00:02 1jsIlW-000157-2d <= root@pppi U=root P=local S=1038

Jul  6 14:00:02 0000000028e33d47 cron[690]: 2020-07-06 14:00:02 1jsIlW-000157-2d Cannot open main log file "/var/log/exim4/mainlog": Permission denied: euid=109 egid=115

Jul  6 14:00:02 0000000028e33d47 cron[690]: exim: could not open panic log - aborting: see message(s) above

Thanks.