In defaults for backups.
include files - default is checked (yes)
this comment:
"Sets the default for including files in a backup. Please note: Disabling this setting will result in a backup which only includes references to files. This is not a problem if the backup is restored on the same site and the files have not been deleted according to the setting 'Clean up trash pool files' (filescleanupperiod)."
That version of Moodle is now 4.1.13+ so your 4.1.1 site is behind a bunch of point
releases.
and
shouldn't --destination=/root/course_test_backup end with a /?
Do you have a file in /root/ by the name of course_test_backup?
If so, see if it is a backup ...
file -b /root/course_test_backup
When a backup is created, moodle does use moodledata/temp/backup/ as a build area.
In above, contenthash folder names contain the build.
Are there any contenthash folders at that location?
If so investigate what's in them ... is there a moodle_backup.xml file?
Is there a backup.mbz file present? IF the latter, the last operation is to copy ... that's copy ... it to destination ... not move. So for a little while disk usage will increase the size of that backup file.
Those contenthash directories should not be present if a backup was successful. They should be cleaned up by a task in the next run of cron job.
'SoS', Ken