OpenBSD: Setup a Serial Console

How do I enable console redirection under OpenBSD so that I can see my remote server boot information and any diagnostic information that is normally printed to the screen? I’ve already enabled serial ports in my server BIOS and wired them up. How do I configure and access OpenBSD UNIX x86/amd64 server over serial console?

OpenBSD operating system supports serial console. You can use the serial console for the following purpose:

Configuration: Setup a serial console

To direct the boot process to use the serial port as a console, edit /etc/boot.conf, enter:
# vi /etc/boot.conf
Edit / append as follows:

set tty com0

The above will use first serial port as your console. You can also define baud rate (default baud rate is set to 9600bps). Append the following line to /etc/boot.conf (set baud rate to 115200):

stty com0 115200

Save and close the file. Reboot the server to test your configuration.

How do I connect to a serial console under Unix/OpenBSD/Linux?

You can also use client tool such as cu, scree, putty (Windows based), and putty for management purpose:
screen /dev/serialdevice 19200,cs8 cu -l /dev/serialdevice -s baud-rate-speed
You can also use minicom, ipmi or KVM over IP clients:
Sample session:

Fig.01: Connected To OpenBSD using KVM serial console

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

1 comment

This was second hit on my google search, so I thought I’d add a comment that might help someone else:

When connecting from an OpenBSD computer, the cu(1) command is available. It has always been part of the OpenBSD base install, and is often overlooked. A simple “cu -l /dev/cua00 -s 115200” will allow you to connect to the serial console. No need to add packages. Note: To leave cu you need to type “~.”, neither Esc nor Ctrl-C will work.

Barry says:
August 23, 2012 at 7:17 pm
This was second hit on my google search, so I thought I’d add a comment that might help someone else:
When connecting from an OpenBSD computer, the cu(1) command is available. It has always been part of the OpenBSD base install, and is often overlooked. A simple “cu -l /dev/cua00 -s 115200” will allow you to connect to the serial console. No need to add packages. Note: To leave cu you need to type “~.”, neither Esc nor Ctrl-C will work.

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