Upgrade to 18 don't work

I have done all as described in documention.

  1. rename nextcloud folder to nextcloud_old
  2. transfer nextcloud18 to server and extract
  3. copy config.php from -old to 18
  4. copy /data from _old to 18

But I’m getting the best known error ‘The server encountered an internal error’.
I have searched the forum for this error and tried all solutions I have found. But still getting that error.
The log files are shown some line, but I can’t identify an error

My server is a armbian (debian stretch) with php7.3
The _old version was 15.?? and was running without any issue

Unfortunately I wouldn’t be possible to help you without any log information. Have you checked the web server log file too? Have you used the occ command to force an upgrade of the database?

I have just seen, that every occ command starts with this error:
An unhandled exception has been thrown:
Doctrine\DBAL\DBALException: Failed to connect to the database: An exception occurred in driver: could not find driver in /var/www/html/nextcloud/lib/private/DB/Connection.php:68

The line 68 include this:
throw new DBALException('Failed to connect to the database: ’ . $e->getMessage(), $e->getCode());

Sorry, don’t know what does this means.

EDIT: Nextcloud error log is empty.
apache2 error.log shows:
[Wed Jan 22 17:42:22.688536 2020] [mpm_prefork:notice] [pid 931] AH00169: caught SIGTERM, shutting down
[Wed Jan 22 17:43:26.441196 2020] [mpm_prefork:notice] [pid 920] AH00163: Apache/2.4.25 (Debian) OpenSSL/1.0.2u configured – resuming normal$
[Wed Jan 22 17:43:26.441585 2020] [core:notice] [pid 920] AH00094: Command line: ‘/usr/sbin/apache2’

I think that’s no errors.

That means that the database specific php module is missing. You have to make sure that you install the php7.3 module, e.g. php7.3-mysql (I don’t know if this is the correct name for your server, so double-check it) if you use MySQL/MariaDB as database.
You should find many matches to this problem when you use the search function of this forum. Make sure that the module is available for the php web AND the cli environment!

The _old version was 15.?? and was running without any issue
Updates over several major releases is not working. I also got this problem when tying to go from 16.xx to 18
There is no other way than
15 -> 16 -> 17 -> 18