sh script works manually but not via cron - shell

Question

I'm trying to run a sh script from crontab. If I run script manually it works perfect, but when I run it in crontab, I get errors.
The script:
#!/bin/bash
sudo tar -zcvf /var/www/nextcloud/data/nextcloud/files/backup.tar.gz /home/beno/stuff/
sudo -u www-data /usr/bin/php /var/www/nextcloud/occ file:scan --all >> /var/www/nextcloud/data/nextcloud/files/backup_log.txt
The script is supposed to make a tar backup of a folder and put it in nextcloud folder and run command files:scan, so nextcloud rescans filesystem and starts synchronization...as I read it here:
https://doc.owncloud.org/server/9.0/admin_manual/configuration_server/occ_command.html#file-operations-label
When crontab runs the script, backup.tar.gz is created, then I get following error:
An unhandled exception has been thrown:
Doctrine\DBAL\DBALException: Failed to connect to the database: An exception occured in driver: SQLSTATE[HY000] [2002] No such file or directory in /var/www/nextcloud/lib/private/DB/Connection.php:60
I'm using ubuntu16 and nextcloud11. Please help!

Answer 1

Following you'r request
Instead of using you'r own crontab, you have to use specic user's crontab, by sudo your crontab command:
sudo -s
then
crontab -e
now you coul add the root's 1st line:
tar -zcvf /var/www/nextcloud/data/nextcloud/files/backup.tar.gz /home/beno/stuff/
and once finished
exit
sudo -s www-data
... and so on...
or (if you could'nt run a shell under www-data):
sudo www-data crontab <<<'01 2 * * * /usr/bin/php /var/www...'
Note: This will overwrite www-data's crontab by this only line!
To prevent this, you could:
sudo www-data crontab -l
to see what contain actual crontab, then
sudo www-data crontab -l |
sed -e '$a 01 2 * * * /usr/bin/php /var/www...'
For adding you'r line, and finally
sudo www-data crontab -l |
sed -e '$a 01 2 * * * /usr/bin/php /var/www...' |
sudo www-data crontab
For replacing actual crontab by modified one.
But it could be simplier to
sudo vi /etc/cron.d/mybackups
Then add you'r rule by following time spec by user name:
21 22 * * * root tar -zcvf /var/w...
22 23 * * * www-data /usr/bin/php /var/www...
Further doc
see man -P'less +/SYSTEM' 5 crontab