solaris下failsafe 是做什么用的？

新手，X86机器进系统在grub界面，可以选择solaris failsafe，这个是用来做什么用的？出什么故障的时候可以用得到？与单用户模式有什么区别呢？谢谢~~

再问下，我在x86系统下使用reboot -- -s命令是进入单用户模式么？
reboot -- -s
重启后有如下提示
booting to milestone "milestone/single-user:default"
requesting  system maintenance mode
single usermode
root password for system maintenance (control-d to bypass)****
single-user privilege assigned to /dev/console.
entering system maintenance mode
#

而如果在grub界面选择solaris failsafe
booting to milestone "milestone/single-user:default"
configuring devices
searching for installer OS instances...
solaris 10 10/09 s10x_u8wos_08a x86 was found on /dev/dsk/c0d0s0.
do you wish to have it mounted read-write on /a?{y,n} y
mounting /dev/dsk/c0d0s0 on /a
starting shell
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这两种方式有啥区别

我一直以为是一回事 ，，坐等有人来普及知识