I get a “Internal Server Error” after following the manual installation of Nextcloud. I check the nextcloud.log file and can read the only message “Failed to start session”. Where can I further investigate this issue?
OS: Arch Linux
Web Server: nginx (mainline) 1.17.1
PHP: 7.3.6
Database: mariadb 10.4.6
I had similar problem and it was due to have not enough RAM in my VPS. In my case it needed 1Gb minimum.
I had just read that in another topic category. I upgraded my VPS to 1GB and will check if i have to reconfigure anything after the upgrade. But there is no immediate solution after upgrading it seems.
Let us to know if your problem has got fixed after the upgrade, please. I think that it’s very interesting to future users with the same problem arriving to this thread 
Unfortunately upgrading the VPS didn’t work for me. I cancelled my 1GB RAM and waited until Ramnode had 2GB RAM in stock (July 2, 2019). I followed the installation like nextcloud docs and arch linux wiki guided. I still get the “Failed to start session” message on my nextcloud.log.
I followed the latest server admin install from docs.nextcloud.com. I think I might’ve just solved my issue. I think the “open_basedir” directive for my php.ini needed the “/dev/urandom” value.
Not sure if any of the guides point that out. Is it necessary?