我已经安装了pepermint 4，但是重新启动后，grub 菜单没有显示，现在它直接启动到Windows。我通过使用启动 USB 中的“尝试薄荷”选项回到薄荷。我也跑过
sudo fdisk -l
这是输出。
Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xd9aacbf3
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 821247 409600 27 Hidden NTFS WinRE
/dev/sda2 821248 489330687 244254720 7 HPFS/NTFS/exFAT
/dev/sda3 489330688 976773119 243721216 7 HPFS/NTFS/exFAT
Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x99954f66
Device Boot Start End Blocks Id System
/dev/sdb1 2048 557340671 278669312 7 HPFS/NTFS/exFAT
/dev/sdb2 * 557340672 557828095 243712 83 Linux
/dev/sdb3 557830142 691828735 66999297 5 Extended
/dev/sdb5 557830144 567828479 4999168 83 Linux
/dev/sdb6 567830528 667828223 49998848 83 Linux
/dev/sdb7 667830272 691828735 11999232 82 Linux swap / Solaris
Disk /dev/sdc: 16.2 GB, 16231956480 bytes
140 heads, 32 sectors/track, 7076 cylinders, total 31703040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc3072e18
Device Boot Start End Blocks Id System
/dev/sdc1 * 32 31703039 15851504 c W95 FAT32 (LBA)薄荷的分区/boot设置为/dev/sdb。
我也尝试过使用键入此代码：
sudo mount /dev/sdb2 /mnt
chroot /mnt
它已成功安装它，但尝试后chroot /mnt它说：
不允许操作。
现在我该怎么做才能启用 grub？