Backup failure due to access denied errors is not logged as an error

If the user who takes the backup does not have the correct permissions on the database server, the backup will fail but it does not indicate this being a permission issue in any way. There is one message about output from the command on the info level:

2025-07-11 14:09:57   notice : [mariadbmon] Backup transferred to SRV

2025-07-11 14:09:57   info   : [mariadbmon] Backup send error output from SRV: [00] 2025-07-11 14:09:54 Connecting to MariaDB server host: localhost, user: foobar, password: set, port: 3306, socket: /var/run/mysqld/mysqld.sock\n[00] 2025-07-11 14:09:54 Failed to connect to MariaDB server: Access denied for user 'foobar'@'localhost' (using password: YES).\n

2025-07-11 14:09:57   error  : [mariadbmon] Directory '/var/lib/mysql' on SRV does not contain file 'backup-my.cnf'. Transfer must have failed.

Checking the error output for Access denied and logging the output as a warning/error would help resolve these sorts of errors a lot quicker.

Comments:
This situation is improved in MaxScale 25.10. If, for example, the monitor user cannot access the server locally, MaxScale log reads:

2025-10-23 12:04:50 notice : [mariadbmon] Backup transferred to server4.
2025-10-23 12:04:50 error : [mariadbmon] Backup send failure on server2. Error 1. Additional details follow.
2025-10-23 12:04:50 error : [mariadbmon] mariabackup: Deprecated program name. It will be removed in a future release, use '/usr/bin/mariadb-backup' instead
2025-10-23 12:04:50 error : [mariadbmon] [00] 2025-10-23 12:04:48 Connecting to MariaDB server host: localhost, user: rebuild_user, password: set, port: not set, socket: not set
2025-10-23 12:04:50 error : [mariadbmon] [00] 2025-10-23 12:04:48 Failed to connect to MariaDB server: Access denied for user 'rebuild_user'@'localhost'.
2025-10-23 12:04:50 error : [mariadbmon] Directory '/var/lib/mysql' on server4 does not contain file 'backup-my.cnf'. Transfer must have failed.

Also, the "fetch-cmd-status"-command shows all available logs from Mariabackup:

maxctrl call command mariadbmon fetch-cmd-status monitor=MyMonitor
.
.
.
{
"errors": [
{
"detail": "Backup send failure on server2. Error 1.",
"meta": {
"errors": [
"mariabackup: Deprecated program name. It will be removed in a future release, use '/usr/bin/mariadb-backup' instead",
"[00] 2025-10-23 14:00:35 Connecting to MariaDB server host: localhost, user: rebuild_user, password: set, port: not set, socket: not set",
"[00] 2025-10-23 14:00:35 Using server version 11.4.8-MariaDB-log",