Sætte boot-flag med CLI

Jeg sidder og sysler med et lille script, der fra kommandolinien kan sætte boot-flaget på en USB-stick. Jeg tænkte sfdisk ville være velegnet, men...
#sfdisk /dev/sdb -N1 ,,,*

sfdisk: can specify only one device (except with -l or -s)
Undlader jeg ",,,*" og giver det interaktivt, brokker den sig:


Checking that no-one is using this disk right now ...
OK

Disk /dev/sdb: 1016 cylinders, 31 heads, 62 sectors/track
Old situation:
Warning: The partition table looks like it was made
for C/H/S=*/16/32 (instead of 1016/31/62).
For this listing I'll assume that geometry.
Units = cylinders of 262144 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/sdb1 0+ 3815 3816- 976880 e W95 FAT16 (LBA)
end: (c,h,s) expected (1023,15,32) found (743,15,32)
/dev/sdb2 0 - 0 0 0 Empty
/dev/sdb3 0 - 0 0 0 Empty
/dev/sdb4 0 - 0 0 0 Empty
Input in the following format; absent fields get a default value.

Usually you only need to specify and (and perhaps ).

/dev/sdb1 :,,,*
Warning: given size (1017) exceeds max allowable size (1016)

/dev/sdb1 :
Nogen der har et hint? Eller et andet bud på at sætte boot-flaget fra kommandolinien.