使用Alt-ScrollLock ，Ctrl-ScrollLock来获得当前系统的backtrace

    我们的linux经常会挂掉，可是并不是说我们不能看到任何信息，我们可以在/var/log/messages里面看到一些信息。

    如果有个process haung掉了，那么我们可以通过Alt-ScrollLock followed by Ctrl-ScrollLock来让系统将当前hang掉的进程以及其他进程的backtrace写入/var/log/messages，当然前提是我们的键盘还可以工作。此外还得满足：

1. The kernel that is running on the system must be built with CONFIG_MAGIC_SYS-REQ enabled. The system must also be in text mode. Pressing Ctrl-Alt-F1 places the system in text mode. Pressing Ctrl-Alt-F7 places the system back in X Window.

2. While in text mode, press Alt-ScrollLock followed by Ctrl-ScrollLock. These magic keystrokes give you a stack trace of the currently running processes and all processes, respectively.

3. Look in the system's /var/log/messages file for the back trace. If everything is set up correctly, the system should have converted the symbolic kernel addresses.