Changes a flag on the disk. A flag can be either “on” or “off”. Some or all of these flags will be available, depending on what disk label you are using:
(GPT) - this flag enables the boot flag on the GPT’s protective MBR partition.
The disk’s flags are displayed by the print command on the "Disk Flags:" line. They are also output as the last field of the disk information in machine mode.
(parted) disk_set pmbr_boot on
Set the PMBR’s boot flag.