Question
Is it safe to remove files mysql.preupgrade.* from the directory /var/lib/psa/dumps/ on a Plesk for Linux server which are created by Plesk automatically?
# ls -lat /var/lib/psa/dumps | grep "mysql.preupgrade"
-rw------- 1 root root 298700 Dec 20 06:20 mysql.preupgrade.apsc.17.8.11-17.8.11.20181220-062042.dump.gz
-rw------- 1 root root 259607 Dec 20 06:20 mysql.preupgrade.17.8.11-17.8.11.20181220-062041.dump.gz
...
-rw------- 1 root root 298800 Dec 10 05:22 mysql.preupgrade.apsc.17.8.11-17.8.11.20181210-052236.dump.gz
-rw------- 1 root root 239266 Dec 10 05:22 mysql.preupgrade.17.8.11-17.8.11.20181210-052235.dump.gz
Answer
Files mysql.preupgrade.* are backups of Plesk system databases that are automatically created before any Plesk upgrade/update.
It is not recommended to remove all files mysql.preupgrade.*.dump.gz, however, it is safe to keep the last backups of each type mysql.preupgrade.apsc and mysql.preupgrade:
# ls -lat /var/lib/psa/dumps | grep "mysql.preupgrade"
-rw------- 1 root root 298700 Dec 20 06:20 mysql.preupgrade.apsc.17.8.11-17.8.11.20181220-062042.dump.gz
-rw------- 1 root root 259607 Dec 20 06:20 mysql.preupgrade.17.8.11-17.8.11.20181220-062041.dump.gz
and remove old backups.