Table of Contents
Slackware can be installed on various embedded devices. A lot of those don't have a traditional console, like a monitor and keyboard. Instead, the console is often routed to the serial port. In order to take advantage of this, some post-install configuration is necessary.
This howto can also be used to setup a serial console on an existing headless server as a backup for administering the machine.
You need to know the serial device and the speed. The device will mostly be ttyS0, the first serial device. If you are using a serial to USB adapter, it will likely be ttyUSB0. Consult the documentation of your board if you are not sure.
Some devices have an option in the BIOS to change the speed and other serial settings. Make sure you know the speed that is currently set.
In the below examples we will assume ttyS0 with speed 38400.
Activate serial port
/etc/inittab and uncomment the correct serial console line. Change
the speed setting when required.
# Local serial lines: s1:12345:respawn:/sbin/agetty -L ttyS0 38400 vt100 #s2:12345:respawn:/sbin/agetty -L ttyS1 9600 vt100
Allow root login
/etc/securetty and uncomment your serial device to allow root to
login via the serial console. You can omit this step if you will access the
machine with a normal user id.
# These are some remote ttys, and uncommenting them might be less than fully secure: ttyS0 #ttyS1
Setup LILO boot loader
/etc/lilo.conf. Add a line to the general section:
The 0 refers to the first serial device, ttyS0.
Add the following parameter to the kernel line:
If the append line already exists, add the parameter as follows:
/sbin/lilo to write the new bootloader configuration.
To have the console on normal tty as well as serial port, adjust the kernel line as follows:
Setup GRUB-legacy boot loader
/boot/grub/menu.lst and change it as follows:
Add lines to the general section as follows:
serial --speed=38400 terminal serial
Add the following parameter to the kernel line:
The complete kernel line might look like this (substitute your root partition and vmlinuz file):
kernel /boot/vmlinuz root=/dev/sda2 ro vga=normal console=ttyS0,38400n8
To have the console on normal tty as well as serial port, adjust the terminal and kernel lines as follows:
terminal --timeout=5 serial console
kernel xxx console=tty0 console=ttyS0,38400n8
When the terminal timeout expires, the first option (in this case serial) will be chosen as the console. The normal bootloader timeout will start when the terminal timeout ends.
Setup GRUB2 boot loader
/etc/default/grub and change the following line to define the console:
Add the following lines to define the console settings:
GRUB_TERMINAL=serial GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"
Now rebuild the GRUB2 configuration:
# grub-mkconfig -o /boot/grub/grub.cfg
Connect from a remote computer
To use the serial console, you need to attach a second computer to the serial port of the host. Use a null modem cable. Most modern computers no longer have a serial port so you might need a serial to USB connector as well.
Once you have physically connected the machines, you need a communications package to interact with the console. Two popular options are screen and minicom.
Connect using screen
This is the easiest option because it doesn't need any configuration. Start screen and specify the serial device and the desired speed on the command line.
user@darkstar$ screen /dev/ttyUSB0 38400
Connect using minicom
Before using minicom, you need to configure it. Start with the
user@darkstar$ minicom -s
You will see the main menu.
+-----[configuration]------+ | Filenames and paths | | File transfer protocols | | Serial port setup | | Modem and dialing | | Screen and keyboard | | Save setup as dfl | | Save setup as.. | | Exit | | Exit from Minicom | +--------------------------+
Select Serial port setup. You will see the serial port settings.
+-----------------------------------------------------------------------+ | A - Serial Device : /dev/ttyS1 | | B - Lockfile Location : /var/lock | | C - Callin Program : | | D - Callout Program : | | E - Bps/Par/Bits : 115200 8N1 | | F - Hardware Flow Control : Yes | | G - Software Flow Control : No | | | | Change which setting? | +-----------------------------------------------------------------------+
Use the A to G keys to change various settings. Make sure the device and Bps/Par/Bits settings are correct. Hit Enter to return to the main screen and select the Modem and dialing option. On the detail screen, make sure the Init string and Reset string options are empty. Hit Enter again to return to the main screen. Now you can save your options. Use Save setup as dfl to save this as your new default. Use Save setup as.. to save as a certain profile.
Call minicom again and the new options will take effect.
Or you can start with a certain configuration
user@darkstar$ minicom myprofile
Use Ctrl+A, Z for help. Use Ctrl+A,X to quit.
Garbled characters in terminal
When you see progress in the terminal but the characters are garbled and unreadable, make sure you have the same speed set in the following sections: BIOS, bootloader and inittab. Also make sure your client connects with the same speed.
Unable to sign on as root
securetty settings. See section above.
Unable to use screen or minicom as a regular user
When you get authorization problems using the serial device, make sure your user is in the
- Originally written by Frank Donkers.