Following report received:

Hi I think there's an error on:
https://mariadb.com/kb/en/library/full-backup-and-restore-with-mariadb-backup/
and likely also affects:
https://mariadb.com/kb/en/library/incremental-backup-and-restore-with-mariadb-backup/
This line: "$ mariabackup --prepare --target-dir /var/mariadb/backup/ \
-user backup_user --password backup_passwd" Should not include the "-user
backup_user --password backup_passwd" part. The comment from Vladislav
Vaintroub (2017-10-27 05:13)
https://jira.mariadb.org/browse/MDEV-14150?jql=text%20~%20%22backup%20prepare%20encryption%22
"--prepare does not need user, or password, it does not contact any
server.. , it does not understand --innodb-encrypt-log either, it is not a
server." explains this. Impact of including the username and password when
attempting to prepare an encrypted backup is the following error on Ubuntu
18 / Centos 7 2018-09-27 15:31:53 0 [ERROR] InnoDB: Obtaining redo log
encryption key version 1 failed (4294967295). Maybe the key or the required
encryption key management plugin was not found. 2018-09-27 15:31:53 0
[ERROR] InnoDB: Reading checkpoint encryption info failed. 2018-09-27
15:31:53 0 [ERROR] InnoDB: No valid checkpoint found (corrupted redo log).
You can try --innodb-force-recovery=6 as a last resort. 2018-09-27 15:31:53
0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error
... fairly challenging to debug so think best to update the page if
possible.