An Arch Linux machine can be configured for connections via the serial console port, which enables administration of a machine even if it has no keyboard, mouse, monitor, or network attached to it.
Mac's are excellent tools for accessing serial device TTY ports (to console into. You can use screen, although Minicom (or a GUI program) offer more features and functionality. Enter the command ls /dev/cu. Add the following line to the bottom of the file: /opt/minicom/2.2/bin, save and exit - then relaunch the terminal. Minicom is a communication program which somewhat resembles the shareware program TELIX but is free with source code and runs under most unices. Features include dialing directory with auto-redial, support for UUCP-style lock files on serial devices, a separate script language interpreter, capture to file, multiple users with individual configurations, and more.
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 Unix/Linux or Windows machine with a terminal emulator program (PuTTY or Minicom, for example).
The configuration instructions below will enable boot loader menu selection, boot messages, and terminal forwarding to the serial console.
- 1Configure console access on the target machine
- 1.1Boot loader
- 2Making Connections
- 2.1Connect using a terminal emulator program
- 2.1.1Command line
- 2.1Connect using a terminal emulator program
- 4Troubleshooting
Configure console access on the target machine
Boot loader
GRUB
When using GRUB with a generated
grub.cfg
, edit /etc/default/grub
and enable serial input and output support:Next add the
GRUB_SERIAL_COMMAND
variable and set the options for the serial connection. For COM1 (/dev/ttyS0
) with baud rate of 115200 bit/s:Read GRUB's manual on Using GRUB via a serial line and the serial command for detailed explanation of the available options.
GRUB Legacy
Edit the GRUB Legacy configuration file
/boot/grub/menu.lst
and add these lines to the general area of the configuration:Note: When the
terminal --timeout=5 serial console
line is added to your menu.lst
, your boot sequence will now show a series of Press any key to continue
messages. If no key is pressed, the boot menu will appear on whichever (serial or console) appears first in the terminal
configuration line.rEFInd
rEFInd supports serial console only in text mode. Edit
refind.conf
and uncomment textonly
.Syslinux
To enable serial console in Syslinux, edit
syslinux.cfg
and add SERIAL
as the first directive in the configuration file.For COM1 (
/dev/ttyS0
) with baud rate of 115200 bit/s:The serial parameters are hardcoded to 8 bits, no parity and 1 stop bit.[1]. Read Syslinux Wiki:Config#SERIAL for the directive's options.
Kernel
Kernel's output can be sent to serial console by setting the
console=
kernel parameter. The last specified console=
will be set as /dev/console
.See https://www.kernel.org/doc/Documentation/admin-guide/serial-console.rst.
getty
At boot, systemd-getty-generator(8) will start a getty instance for each console specified in the kernel command line.
If you have not configured
console=
in kernel command line startserial-getty@device.service
. For /dev/ttyS0
(COM1) that would be [email protected]
. Enable the service to start it at boot. Unless specified otherwise in the kernel command line, getty will be expecting 38400 bit/s baud rate, 8 data bits, no parity and one stop bit-times.
Making Connections
Connect using a terminal emulator program
Note: Before making a connection, it is recommended to add your user to the
uucp
group. Otherwise you will need root's permission to make a connection:See Users and groups#User groups for details.Perform these steps on the machine used to connect the remote console.
Command line
dterm
dtermAUR is a tiny serial communication program. If you invoke it without parameters, it will connect to
/dev/ttyS0
at 9600 baud by default. The following example connect to /dev/ttyS0
at 115200 baud, with 8 data bits, no parity bit and 1 stop bit-times:See its homepage[2] for more examples.
Minicom
minicom can be obtained from the official repositories. Start Minicom in setup mode:
Using the textual navigation menu, change the serial port settings to the following:
Press Enter to exit the menus (pressing Esc will not save changes).Remove the modem Init and Reset strings, as we are not connecting to a modem. To do this, under the
Modem and Dialing
menu, delete the Init and Reset strings. Optionally save the configuration by choosing save setup as dfl
from the main menu.Restart minicom with the serial cable connected to the target machine.To end the session, press Ctrl+A
followed by Ctrl+X
.picocom
picocom is a tiny dumb-terminal emulation program that is very like minicom, but instead of mini, it is pico. The following example connect to
ttyS0
at 9600 bps:![Line Line](/uploads/1/2/6/4/126470752/708276156.png)
Note: if the backspace key won't work properly try out this option: '--omap delbs'
See its manual for detailed usage.
Screen
GNU Screen is able to connect to a serial port. It will connect at 9600 baud by default:
A different baud rate (e.g. 115200) may be specified on the command line.
To end the session, press
Ctrl+a
followed by K
. Alternatively, press Ctrl+a
, type :quit
and confirm it by pressing Enter
.Serialclient
Serialclient[3] is a CLI client for serial connection written in ruby. Install it with the following:
Then, you can use like this:
And, for Windows
On Windows machines, connect to the serial port using programs like PuTTY[4] or Terminalbpp[5].
Graphical front-ends
cutecomAUR is another gui enabled serial monitor.
putty is also available for Linux.
moserial is a gtk-based serial terminal, primarily intended for technical users and hardware hackers who need to communicate with embedded systems, test equipment, and serial consoles.
Installing Arch Linux using the serial console
Note: The Arch Linux monthly release(i.e. the installation CD)'s boot loader has been configured[6] to listen on 0 port(
ttyS0
/COM1) at 38400 bps, with 8 data bits, no parity bit and 1 stop bit-times.- Connect to the target machine using the method described above.
- Boot the target machine using the Arch Linux installation CD.
- When the bootloader appears, select Boot Arch Linux (<arch>) and press
Tab
to edit - Append
console=ttyS0,38400
and pressEnter
. - Now systemd should detect ttyS0 and spawn a serial getty on it. Login as
root
and start the installation as usual.
Note: 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: While a port speed of 9600 is used in most 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.
Resizing a terminal
Unlike ssh, serial connections do not have a mechanism to transfer something like
SIGWINCH
when a terminal is resized. This can cause weird problems with some full-screen programs (e.g. less
) when you resize your terminal emulator's window.Resizing the terminal via
stty
is a workaround:However, this requires you to manually input the proper geometry. The following methods should be simpler.
1. There is a lesser-known utility called
resize
, shipped with xterm, that can solve this problem. Invoke it without parameters after you resize the terminal emulator's window:2. If you don't want to install xterm, it is possible to do the same work via a shell function. Put the following function into your zshrc and invoke it without parameters after resizing the terminal emulator's window:
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