Working with the serial console

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Introduction

Configure your Arch Linux machine, so you can connect to it via the serial console port (com port). This will enable you to administer the machine, even if it has no keyboard, mouse, monitor or network attached to it (a headless server).

As of Arch Linux 2007.x, installation of Arch Linux is possible via the serial console as well.

A basic environment for this scenario is two machines, connected using a serial cable (9-pin connector cable). The administering machine can be any Linux or Windows machine with a terminal emulator program (putty or Minicom for example)

The configuration instructions below will enable grub menu selection, boot messages and terminal forwarding to the serial console.

Configuration

Configure console access on the target machine

1. Edit the grub.conf file:

# vi /boot/grub/menu.lst

Add these lines to the general area of the configuration:

serial --unit=0 --speed=9600
terminal --timeout=5 serial console

Add the console parameters at the end of your current kernel line:

console=tty0 console=ttyS0,9600

For example, the kernel line should look something like this after modification:

kernel /vmlinuz26 root=/dev/md0 ro md=0,/dev/sda3,/dev/sdb3 vga=773 console=tty0 console=ttyS0,9600

2. Edit the inittab file:

# vi /etc/inittab

Add a new agetty line below the existing ones :

c0:2345:respawn:/sbin/agetty 9600 ttyS0 linux

3. Edit the securetty file:

# vi /etc/securetty

Below the existing tty's add an entry for the the serial console:

ttyS0

4. Reboot the machine

Note that in all of the steps above ttyS1 can also be used, in case that your machine has more than one serial port.

Making Connections

Connect using a terminal emulator program

Perform these steps on the machine used to connect the remote console.

Minicom

1. Install Minicom:

# pacman -S minicom

2. Start Minicom in setup mode:

# minicom -s

3. Using the textual navigation menu change the serial port settings to the following:

Serial Device: /dev/ttyS0
Bps/Par/Bits: 9600 8N1

Press Enter to exit the menus (pressing Esc will not save changes)

4. Remove the modem Init and Reset strings:

Under the 'Modem and Dialing' menu delete the Init and Reset strings.

5. Save the setup:

From the main menu, choose 'save setup as dfl'

6. Exit Minicom:

From the main menu, choose 'Exit from Minicom'

7. Connect to the target machine:

While the serial cable is connected to the target machine, start the Minicom program:

# minicom

8. Exiting Minicom

To finish the session press 'ctrl-A' and then 'X'.

Screen

Screen is able to connect to a serial port. It will connect to a standard 9600 speed port without options.

# screen /dev/ttyS0

If needed see the section "WINDOW TYPES" in the screen man page for details on setting the baud rate.

Windows Options

On Windows machines, connect to the serial port using programs like Putty or Hyper Terminal.

Installing Arch Linux using the serial console

1. Connect to the target machine using the method described above.

2. Boot the target machine using the Arch Linux installation CD.

After a while, output from the console will start showing on screen and setup can be started normally.

Note that after setup is complete, the console settings will not be saved on the target machine, in order to avoid having to connect a keyboard and monitor, configure console access on the target machine before rebooting.

Note that while a port speed of 9600 is used in all of the examples in this document, working with higher values is recommended (List of available speeds is displayed in Minicom by pressing 'Ctrl-A' and then 'P')

Troubleshooting

Ctrl-C and Minicom

If you are having trouble sending a Control-C command through minicom you need to switch off hardware flow control in the device settings (minicom -s), which then enables the break.