mysqldump: Got errno 28 on write
ERROR: mysqldump command did not succeed.
You are backing up your MYSQL database using mysqldump command line tool and you encounter the above error message. In my case I was outputting my mysql backup database file to an external usb drive.
The issue here was that my external usb drive had run out of free disk space and the above error means that sufficient disk space is not available to do backups.
To resolve this problem, simply free up disk space and re-run the mysqldump command line tool for MySQL to backup your database.