Ok so i sort of replicated this on my daily branch, my other release branch server is ok but different environment completely.
librenms user is in the www-data group
Click “New Device Group” - Something went wrong, check logs/librenms.log
Full Stack trace https://pastebin.com/raw/qUkPzWZU
devices_relationships.cache was owned by librenms:librenms
File: devices_relationships.cache
Size: 5979 Blocks: 16 IO Block: 4096 regular file
Device: 801h/2049d Inode: 1182620 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 999/librenms) Gid: ( 999/librenms)
Access: 2019-07-11 16:16:17.716875995 +0100
Modify: 2019-07-09 10:23:10.813061295 +0100
Change: 2019-07-11 16:15:42.915964900 +0100
Birth: -
Then i was just playing around,
chown librenms:www-data devices_relationships.cache (didn’t work)
chown www-data:www-data devices_relationships.cache (worked, can now create device group)
changed back:
chown librenms:www-data devices_relationships.cache (worked , didn’t before)
chown librenms:librenms devices_relationships.cache (works again, don’t see what changed)
Hope that might help 