Linux Serial Console
Linux support for a serial console is a
very useful feature. It allows running a Linux box in a headless
configuration without a monitor or keyboard. This is very common in
server rooms where there are racks of servers.
It also can come in handy at home. Since I
have two computers and only one monitor, it really helps. My main
computer runs Windows 2000 and my lesser computer runs Linux. Normally,
the Linux computer is accessed completely through the network. But
every one in a while, it needs administration help. Then, a serial
console comes in handy. Only in true emergencies or when reinstalling
the operating system do I need to connect a monitor and keyboard.
I use
as a boot loader. GRUB supports sending its messages to the serial
console. The following lines should be added to the top of the
/boot/grub/grub.conf
file.
serial –unit=0 –speed=9600terminal –timeout=10 serial console
The following parameters need to be passed to each instance of the linux kernel. They should be added to the
kernel
line. It would be helpful if GRUB
supported variable substitution so that the parameters only needed to
be defined in one place.
console=tty0 console=ttyS0,9600
Linux needs to be told to listen for logins on the serial port. This is done by adding the following line to
/etc/inittab
. The
115200,9600
part indicates it should start at 115200 and then downgrade to 9600 if it receives junk indicating a speed mismatch.
s0:2345:respawn:/sbin/agetty ttyS0 115200,9600 linux
To connect another computer to the serial port, you need a null modem cable. Or a null modem adapter and regular serial.
On Windows, I use SecureCRT as the terminal program. Unluckily, the excellent open source doesn’t support serial ports.
It is also possible to connect a Palm
handheld to a serial port using a serial HotSync cable. Unluckily, the
newer Palms use USB HotSync cables instead of serial cables. It is
possible to buy serial HotSync cable for most models but I haven’t yet
tried it. It is also possible to get IrDA to serial adapters to
communicate through the Palm’s IR port. Use a terminal application like
on the Palm. The usability is poor because of the small screen size and lack of keyboard but you can’t beat the portability.
简单来说，就是
1.修改/boot/Grub/menu.lst文件，在文件中添加
serial –unit=0 –speed=9600
terminal –timeout=0 serial console
(–timeout设置为零，启动直接进入grub，不用再等了)
2.修改/boot/Grub/menu.lst文件，在kernel=*** root=*** 后面添加console=tty0 console=ttyS0 , 9600
3.修改inittab.
添加一行：s0:2345:respawn:/sbin/agetty ttyS0 9600
通过windows的超级终端进入系统，系统提示输入用户名和密码，之前需要先按键盘Scroll Lock键，否则键盘不能用。
当然，内核也要支持串口才行。
Device Drivers–>Character devices–>Serial drivers