あいかわらずブートフラグがないねえ
$ sudo sfdisk --list /dev/sdb
Disk /dev/sdb: 59.5 GiB, 63864569856 bytes, 124735488 sectors
Disk model: Card Reader
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0634f60c
Device Boot Start End Sectors Size Id Type
/dev/sdb1 8192 532480 524289 256M c W95 FAT32 (LBA)
/dev/sdb2 540672 4292607 3751936 1.8G 83 Linux