parted: disk_set
2.4.2 disk_set
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-- Command: disk_set FLAG STATE
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:
'pmbr_boot'
(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.