最近，我在一台多年来一直使用 FreeBSD 6.2 运行良好的机器上安装了 FreeBSD 10.1。由于机器位于数据中心，我通过串行控制台配置了远程访问。
安装后，我在启动时遇到了一个奇怪的问题。每次重启都无法挂载 rootfs。
uhub4: 8 ports with 8 removable, self powered
Trying to mount root from ufs:/dev/raid/r0p2 [rw]...
mountroot: waiting for device /dev/raid/r0p2 ...
Mounting from ufs:/dev/raid/r0p2 failed with error 19.
Loader variables:
vfs.root.mountfrom=ufs:/dev/raid/r0p2
vfs.root.mountfrom.options=rw
Manual root filesystem specification:
<fstype>:<device> [options]
Mount <device> using filesystem <fstype>
and with the specified (optional) option list.
eg. ufs:/dev/da0s1a
zfs:tank
cd9660:/dev/acd0 ro
(which is equivalent to: mount -t cd9660 -o ro /dev/acd0 /)
? List valid disk boot devices
. Yield 1 second (for background tasks)
<empty line> Abort manual input
mountroot>
但当我按下 Enter 键（通过连接的键盘或串行控制台）时，我可以看到以下内容，系统重新启动正常
mountroot>
panic: mountroot: unable to (re-)mount root.
cpuid = 0
KDB: stack backtrace:
#0 0xffffffff80963000 at kdb_backtrace+0x60
#1 0xffffffff80928125 at panic+0x155
#2 0xffffffff809c554f at vfs_mountroot+0x1eaf
#3 0xffffffff808d7533 at start_init+0x53
#4 0xffffffff808f8b6a at fork_exit+0x9a
#5 0xffffffff80d0acbe at fork_trampoline+0xe
Uptime: 12s
Automatic reboot in 15 seconds - press a key on the console to abort
现在系统重新启动，一切正常
Trying to mount root from ufs:/dev/raid/r0p2 [rw]...
Setting hostuuid: 530c9cf5-a7e5-11e4-97b5-00e08146563c.
Setting hostid: 0xe4218f4f.
Entropy harvesting: interrupts ethernet point_to_point swi.
Starting file system checks:
/dev/raid/r0p2: FILE SYSTEM CLEAN; SKIPPING CHECKS
/dev/raid/r0p2: clean, 7232943 free (983 frags, 903995 blocks, 0.0% fragmentation)
/dev/raid/r1s1f: FILE SYSTEM CLEAN; SKIPPING CHECKS
/dev/raid/r1s1f: clean, 41630678 free (104646 frags, 5190754 blocks, 0.1% fragmentation)
/dev/raid/r0p4: FILE SYSTEM CLEAN; SKIPPING CHECKS
/dev/raid/r0p4: clean, 49146170 free (8498 frags, 6142209 blocks, 0.0% fragmentation)
Mounting local file systems:.
Writing entropy file:.
我只是认为，如果系统在无法挂载根目录时自动重新启动（我猜是由于内核恐慌），我就可以让这个系统正常工作，它只会重新启动两次。
我找到了类似的线程，但与 Linux 相关，我可以在其中设置 /etc/sysctl 变量并让系统在内核崩溃时自动重启
kernel.panic = 20
但它似乎在 FreeBSD 上不起作用。我的问题是，当无法挂载 rootfs 时，有没有办法让这个系统自动重启？我希望它可以在第二次运行时重新启动并挂载 root？
我也会很感激任何其他建议。
谢谢
评论1：
我被要求从服务器设置中输出一些数据，如下所示：
nn@d02:~ % uname -a
FreeBSD hostname 10.1-RELEASE-p19 FreeBSD 10.1-RELEASE-p19 #0: Sat Aug 22 03:55:09 UTC 2015 [email protected]:/usr/obj/usr/src/sys/GENERIC amd64
nn@d02:~ % freebsd-version -k
10.1-RELEASE-p19
nn@d02:~ % freebsd-version -u
10.1-RELEASE-p19
nn@d02:~ % gpart show
=> 34 488390589 raid/r0 GPT (233G)
34 1024 1 freebsd-boot (512K)
1058 62914560 2 freebsd-ufs (30G)
62915618 8388608 3 freebsd-swap (4.0G)
71304226 417086396 4 freebsd-ufs (199G)
488390622 1 - free - (512B)
=> 63 488390593 raid/r1 MBR (233G)
63 488375937 1 freebsd [active] (233G)
488376000 14656 - free - (7.2M)
=> 0 488375937 raid/r1s1 BSD (233G)
0 1048576 1 freebsd-ufs (512M)
1048576 8324192 2 freebsd-swap (4.0G)
9372768 6258688 4 freebsd-ufs (3.0G)
15631456 1048576 5 freebsd-ufs (512M)
16680032 471695905 6 freebsd-ufs (225G)
nn@d02:~ % graid show
graid: Unknown command: show.
nn@d02:~ % graid status
Name Status Components
raid/r0 OPTIMAL ada0 (ACTIVE (ACTIVE))
ada1 (ACTIVE (ACTIVE))
raid/r1 OPTIMAL ada2 (ACTIVE (ACTIVE))
ada3 (ACTIVE (ACTIVE))
答案1
GENERIC如果您在 FreeBSD 中使用内核，则该KDB选项与 sysctl 一起启用debug.debugger_on_panic，默认在出现问题时进入内核调试器进行故障排除。
要停止调用调试器，请将 sysctl 更改debug.debugger_on_panic为0按照内核调试选项词汇表。这应该可以解决您在发生恐慌时需要在场才能与服务器交互的问题。
希望这对你有帮助。祝你好运。=)