客户使用 yum update 将其 EC2 CentOS 6.4 实例更新到 6.9。更新并重新启动后，实例将不再启动（变得无法访问）
系统日志（从 AWS 控制台恢复）如下所示：
Xen Minimal OS!
start_info: 0x10d3000(VA)
nr_pages: 0xe4f53
shared_inf: 0xeea31000(MA)
pt_base: 0x10d6000(VA)
nr_pt_frames: 0xd
mfn_list: 0x9ab000(VA)
mod_start: 0x0(VA)
mod_len: 0
flags: 0x300
cmd_line: root=/dev/sda1 ro console=hvc0 4
stack: 0x96a100-0x98a100
MM: Init
_text: 0x0(VA)
_etext: 0x7b824(VA)
_erodata: 0x97000(VA)
_edata: 0x9cce0(VA)
stack start: 0x96a100(VA)
_end: 0x9aa700(VA)
start_pfn: 10e6
max_pfn: e4f53
Mapping memory range 0x1400000 - 0xe4f53000
setting 0x0-0x97000 readonly
skipped 0x1000
MM: Initialise page allocator for 1807000(1807000)-e4f53000(e4f53000)
MM: done
Demand map pfns at e4f54000-20e4f54000.
Heap resides at 20e4f55000-40e4f55000.
Initialising timer interface
Initialising console ... done.
gnttab_table mapped at 0xe4f54000.
Initialising scheduler
Thread "Idle": pointer: 0x20e4f55050, stack: 0xe4810000
Thread "xenstore": pointer: 0x20e4f55800, stack: 0xe4820000
xenbus initialised on irq 3 mfn 0xfeffc
Thread "shutdown": pointer: 0x20e4f55fb0, stack: 0xe4830000
Dummy main: start_info=0x98a200
Thread "main": pointer: 0x20e4f56760, stack: 0xe4840000
"main" "root=/dev/sda1" "ro" "console=hvc0" "4"
vbd 2048 is hd0
******************* BLKFRONT for device/vbd/2048 **********
backend at /local/domain/0/backend/vbd/2334/2048
629145600 sectors of 512 bytes
**************************
vbd 2128 is hd1
******************* BLKFRONT for device/vbd/2128 **********
backend at /local/domain/0/backend/vbd/2334/2128
314572800 sectors of 512 bytes
**************************
[H[J
GNU GRUB version 0.97 (3751244K lower / 0K upper memory)
[m[4;2H+-------------------------------------------------------------------------+[5;2H|[5;76H|[6;2H|[6;76H|[7;2H|[7;76H|[8;2H|[8;76H|[9;2H|[9;76H|[10;2H|[10;76H|[11;2H|[11;76H|[12;2H|[12;76H|[13;2H|[13;76H|[14;2H|[14;76H|[15;2H|[15;76H|[16;2H|[16;76H|[17;2H+-------------------------------------------------------------------------+[m
Use the ^ and v keys to select which entry is highlighted.
Press enter to boot the selected OS, 'e' to edit the
commands before booting, or 'c' for a command-line.[5;78H [m[7m[5;3H CentOS (2.6.32-696.18.7.el6.x86_64) [5;75H[m[m[6;3H CentOS (2.6.32-573.el6.x86_64) [6;75H[m[m[7;3H CentOS (2.6.32-358.18.1.el6.x86_64) [7;75H[m[m[8;3H CentOS-6.4-x86_64-GA-03 2.6.32-358.el6.x86_64 [8;75H[m[m[9;3H [9;75H[m[m[10;3H [10;75H[m[m[11;3H [11;75H[m[m[12;3H [12;75H[m[m[13;3H [13;75H[m[m[14;3H [14;75H[m[m[15;3H [15;75H[m[m[16;3H [16;75H[m[16;78H [5;75H[23;4H The highlighted entry will be booted automatically in 1 seconds. [5;75H[H[J Booting 'CentOS (2.6.32-696.18.7.el6.x86_64)'
root (hd0)
Filesystem type is ext2fs, using whole disk
kernel /boot/vmlinuz-2.6.32-696.18.7.el6.x86_64 root=/dev/xvde ro crashkernel=a
uto LANG=en_US.UTF-8 KEYTABLE=us
initrd /boot/initramfs-2.6.32-696.18.7.el6.x86_64.img
============= Init TPM Front ================
Tpmfront:Error Unable to read device/vtpm/0/backend-id during tpmfront initialization! error = ENOENT
Tpmfront:Info Shutting down tpmfront
close blk: backend=/local/domain/0/backend/vbd/2334/2048 node=device/vbd/2048
close blk: backend=/local/domain/0/backend/vbd/2334/2128 node=device/vbd/2128
我们对 AWS 都没有太多经验，所以我们不知道该怎么做。知道我们应该关注什么或有什么可以为我们指明正确的方向吗？该实例实际上是生产的克隆，我们在实际生产中进行升级之前对其进行了测试，因此我们有机会再次尝试并在更新之前或之后调整任何设置或其他内容。