由于长久不用Air了，所以忘记了之前的root密码，导致很多命令都无法执行，于是找到了这个解决方法（经本人在Mac os x 10.6.8下测试成功！），故来跟大家分享下。
开机，并迅速按住 Command + S组合键，进入命令行模式
输入命令(有时可能要命令路径不同，可参考屏幕上显示的那两行提示),检查系统错误并修复
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/sbin/fsck -fy
输入命令,使有权限更改系统配置
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/sbin/mount -uw /
最后根据命令
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passwd root
来更改密码就ok啦！
然后 敲入 reboot 命令，重启机器就完工啦！
以下是原文：
Change an Admin Password in Mac OS X Single User Mode
This is a multistep process but it’s easy to follow:
First you need to enter Single User Mode. Reboot the Mac and hold down Command+S at boot to enter into the command line.
You’ll see a note where Mac OS X tells you that you need to run two commands in order to make filesystem changes, this is necessary so let’s handle that first
The first command checks the Mac OS X filesystem for errors and fixes them, it can take a few minutes to run:
fsck -fy
The next command mounts the root Mac OS X drive as writable, allowing you to make changes to the filesystem:
mount -uw /
After the filesystem is mounted, you can reset any users password using the following command:
passwd username
You’ll need to enter the new password twice to reset and confirm the changes