When importing huge SQL dumps back into phpmyadmin sometimes the import will be interrupted by time outs. To solve this it is possible to increase the Execution time of the import mechanism, or even better: set the execution time limit to infinite.
To do this open the in your phpmyadmin folder the /phpmyadmin/libraries/config.default.php file and change:

$cfg['ExecTimeLimit'] = 300;

to

$cfg['ExecTimeLimit'] = 0; (zero means: no limit!)

After a restart of the apache server (service apache2 restart or systemctl restart apache2) there will not be any time out when uploading/importing SQL-dump files.