If you are running RedHat 9.0 and want to run “headless” (no monitor, keyboard, or mouse) but still want to have a console to receive console messages or login, here are the basics of what I did to get it working.

This example will set up a serial console on Com 1 (ttyS0) at 38.4K Baud, Data bits 8, Parity None, 1 stop bit.

Requirements:

* agetty – alternative Linux getty – agetty is included in the RedHat 9.0 Installation (unless you chose not to install it)
* A Null Modem Cable – To connect to your PC, laptop, or terminal. You can make one yourself or pick one up from Radio Shack for a few bucks.
* Running lilo as your boot loader.
* Support for console on serial port must be compiled into the kernel (not loaded as a module) This option is located under Character devices – it is compiled in by default on Redhat 9 installations.
* Root access.

Make sure you set up your BIOS to continue on Keyboard or Mouse errors. Some machines will allow you to ignore these errors specifically, on others you may have to configure it to continue on any error.

In /etc/lilo.conf add this to the global section:

serial = 0,38400n8

Then add this to the append line in the kernel section:

append = “console=ttyS0,38400n8″

If you are already using an append for other options just add console=ttyS0,38400n8 to the end of those. Once you have made the changes to /etc/lilo.conf remember to run /sbin/lilo to set the new configuration for the next boot.

To enable the ability to login on to the machine using the serial console add the following line to /etc/inittab:

s0:12345:respawn:/sbin/agetty -i -h -L 38400 ttyS0 vt100

Connect the null modem cable to Com 1 and then to your PC, Laptop, or Terminal. Configure the connection (terminal program) for 38400 baud (38.4k), 8 data bits, parity none, and stop bits 1. (On windows you can connect using Hyperterminal, TeraTerm, or any other terminal program that supports serial ports. On a Linux machine you can use minicom).

Now reboot the linux box that you configured the serial console on and monitor the connection. You should see the kernel decompress and then the boot messages over your serial connection. Once the machine has finished booting you should receive a logon prompt on the console.

If you receive a bunch of garbage on the terminal check your baud and parity settings. If you do not receive a logon prompt check you inittab configuration and make sure agetty is running on ttyS0 (ps -ef | grep agetty).

For more help check out the man pages for agetty, lilo, lilo.conf, and inittab.

You can also try a google search for linux serial console, there are a lot of other similar ways to do this.

Here is the quick and dirty configuration for bonding two Serial (T1) PPP links on a Cisco 1841 router.

interface Mulitlink1
ip address xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
ppp multilink
ppp multilink group 1

interface Serial 0/0
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 1

interface Serial 0/1
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 1

The two serial interfaces then look like one – the Multilink1 interface.  The PPP ip address for this end will be the ip address of the Multilink1 interface. You can still check the status of each serial interface using “show interface serial 0/x” .  This will also show you what Multilink group the serial interface is a member of

Link is a member of Multilink bundle Multilink1

You can also check the status of the Multilink interface by using “show interface Multilink1″.  The command “show ppp multilink interface multilink1″ will display what interfaces belong to the multilink group (useful if you are on a larger router with multiple multilink ppp groups).

I have set up these multilink interfaces in the past, but I can say I am not sure what happens if just one of the T1s fail.  I would guess that the PPP would not like this and bring the whole interface down.

Does losing one T1 bring the whole Multilink interface down or will it the protocol stay up? Is there a better way to do this that will keep the interface up if one of the T1s fail?

Going to have to test this when I get a chance.