Difference between revisions of "Working with the serial console"

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m (Minicom: fixed package link)
(Bit of a tidy-up, mainly changing configuration blocks from {{ic}} to code blocks)
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====GRUB2 and systemd====
 
====GRUB2 and systemd====
  
If you configure the serial console in GRUB2 systemd will create a getty listener on the same serial device as GRUB2 by default. So, this is the only configuration needed for Arch running with systemd.
+
If you configure the serial console in GRUB2 systemd will create a getty listener on the same serial device as GRUB2 by default. So, this is the only configuration needed for Arch running with systemd. To make grub enable the serial console, open {{ic|/etc/default/grub}} in an editor.
<br><br>
+
Change the {{ic|GRUB_CMDLINE_DEFAULT}} line to start the console on {{ic|/dev/ttyS0}}. Note in the example below, we set two consoles up; one on tty0 and one on the serial port.
Edit /etc/default/grub
+
  GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,38400n8"
<br><br>
 
1. Edit the GRUB_CMDLINE_DEFAULT="" line to start the console on /dev/ttyS0<br>
 
{{ic|<nowiki>
 
GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,38400n8"
 
</nowiki>}}
 
<br><br>
 
2. Add a serial console section<br>
 
{{ic|<nowiki>
 
# Serial console</nowiki><br>
 
<nowiki>GRUB_TERMINAL=serial</nowiki><br>
 
<nowiki>GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"
 
</nowiki>}}
 
<br><br>
 
3. Rebuild the grub.cfg file<br>
 
{{ic|<nowiki>
 
grub-mkconfig > /boot/grub/grub.cfg
 
</nowiki>}}
 
<br><br>
 
Now you are done. After reboot getty will be listening on device /dev/ttyS0 with settings 38400 8N1 and systemd will automatically start a getty session to listen on the same device with the same settings.
 
  
=====Without GRUB2, systemd only=====
+
Now we've got to tell grub what command to start in order to enable the serial console:
This step is not needed if you have configured GRUB2 to listen on the serial interface. If you do not want GRUB2 to listen on the serial device, but only want getty listening after boot then follow these steps.
+
 
<br><br>
+
  # Serial console
1. To start getty listening on /dev/ttyS0 use systemctl<br>
+
  GRUB_TERMINAL=serial
{{ic|<nowiki>
+
  GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"
systemctl start getty@ttyS0.service
+
 
</nowiki>}}
+
Rebuild the grub.cfg file
<br><br>
+
  # grub-mkconfig -o /boot/grub/grub.cfg
You can check to see the speed getty is useing with systemctl, but should be 38400 8N1<br>
 
{{ic|<nowiki>
 
systemctl status serial-getty@ttyS0.service
 
</nowiki>}}
 
<br><br>
 
2. To have getty listening on /dev/ttyS0 every boot create this symlink
 
{{ic|<nowiki>
 
ln -s /usr/lib/systemd/system/serial-getty@.service  /etc/systemd/system/getty.target.wants/serial-getty@ttyS0.service
 
</nowiki>}}
 
<br><br>
 
Now after reboot getty will be listening on device /dev/ttyS0 with settings 38400 8N1
 
  
====GRUB v1 and No systemd====
+
After a reboot, getty will be listening on {{ic|/dev/ttyS0}}, expecting 38400 baud, 8 data bits, no parity and one stop bit. When Arch boots, systemd will automatically start a getty session to listen on the same device with the same settings.
  
1. Edit the GRUB config file:
+
=====Without GRUB2, systemd only=====
 +
Ignore this entire section if you have configured GRUB2 to listen on the serial interface. If you do not want GRUB2 to listen on the serial device, but only want getty listening after boot then follow these steps.
  
vi /boot/grub/menu.lst
+
To start getty listening on {{ic|/dev/ttyS0}} use systemctl
 +
  systemctl start getty@ttyS0.service
  
Add these lines to the general area of the configuration:
+
You can check to see the speed(s) getty is using with systemctl, but should be 38400 8N1
  
{{ic|<nowiki>
+
  systemctl status serial-getty@ttyS0.service
serial --unit=0 --speed=9600</nowiki><br>
 
<nowiki>terminal --timeout=5 serial console</nowiki>
 
}}
 
  
Add the console parameters at the end of your current kernel line:
+
To have getty listening on {{ic|/dev/ttyS0}} every boot, enable the service for that specific port.
  
{{ic|<nowiki>
+
  systemctl enable serial-getty@ttyS0.service
console=tty0 console=ttyS0,9600
 
</nowiki>}}
 
  
For example, the kernel line should look something like this after modification:
+
Now, after a reboot, getty will be listening on device {{ic|/dev/ttyS0}} expecting 38400 baud, 8 data bits, no parity and one stop bit
  
{{ic|<nowiki>
+
====GRUB v1 and No systemd====
kernel /vmlinuz-linux root=/dev/md0 ro md=0,/dev/sda3,/dev/sdb3 vga=773 console=tty0 console=ttyS0,9600
+
Edit the GRUB config file {{ic|/boot/grub/menu.lst}} and add these lines to the general area of the configuration:
</nowiki>}}
 
  
{{note|When the {{ic|<nowiki>terminal --timeout=5 serial console</nowiki>}} line is added to your menu.lst grub configuration, 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.  The lines will look like this upon boot:}}
+
  serial --unit=0 --speed=9600
 +
  terminal --timeout=5 serial console
  
{{ic|
+
Add suitable console parameters (e.g. change the serial device name or baud rate if required) at the end of your current kernel line:
Press any key to continue.<br>
 
Press any key to continue.<br>
 
Press any key to continue.<br>
 
Press any key to continue.<br>
 
Press any key to continue.<br>
 
Press any key to continue.<br>
 
Press any key to continue.
 
}}
 
  
2. Edit the inittab file:
+
  console=tty0 console=ttyS0,9600
  
vi /etc/inittab
+
For example, the kernel line should look something like this after modification:
  
Add a new agetty line below the existing ones:
+
  kernel /vmlinuz-linux root=/dev/md0 ro md=0,/dev/sda3,/dev/sdb3 vga=773 console=tty0 console=ttyS0,9600
  
 +
{{note|When the {{ic|<nowiki>terminal --timeout=5 serial console</nowiki>}} line is added to your menu.lst grub configuration, 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.  The lines will look like this upon boot:}}
 
{{ic|
 
{{ic|
c0:2345:respawn:/sbin/agetty 9600 ttyS0 linux
+
  Press any key to continue.<br>
 +
  Press any key to continue.<br>
 +
  Press any key to continue.<br>
 +
  Press any key to continue.<br>
 +
  Press any key to continue.<br>
 +
  Press any key to continue.<br>
 +
  Press any key to continue.
 
}}
 
}}
  
3. Edit the securetty file:
+
Next, we have to edit {{ic|/etc/inittab}} and add a new agetty line below the existing ones:
  
vi /etc/securetty
+
  c0:2345:respawn:/sbin/agetty 9600 ttyS0 linux
  
Below the existing ttys, add an entry for the the serial console:
+
Edit {{ic|/etc/securetty}} and add an entry for the the serial console, ''below the existing entries'':
  
{{ic|
+
  ttyS0
ttyS0
 
}}
 
  
4. Reboot the machine
+
Reboot.
  
 
{{note|In all of the steps above, ttyS1 can also be used in case your machine has more than one serial port.}}
 
{{note|In all of the steps above, ttyS1 can also be used in case your machine has more than one serial port.}}
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====Minicom====
 
====Minicom====
  
1. Install {{Pkg|minicom}}:
+
{{Pkg|minicom}} can be obtained from the official repositories. Start Minicom in setup mode:
 
 
pacman -S minicom
 
 
 
2. Start Minicom in setup mode:
 
  
 
  minicom -s
 
  minicom -s
  
3. Using the textual navigation menu, change the serial port settings to the following:
+
Using the textual navigation menu, change the serial port settings to the following:
  
{{ic|
+
  Serial Device: /dev/ttyS0
Serial Device: /dev/ttyS0<br>
+
  Bps/Par/Bits: 9600 8N1
Bps/Par/Bits: 9600 8N1
 
}}
 
  
 
Press Enter to exit the menus (pressing Esc will not save changes).
 
Press Enter to exit the menus (pressing Esc will not save changes).
 
+
Remove the modem Init and Reset strings, as we're 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.
4. Remove the modem Init and Reset strings:
+
Restart minicom with the serial cable connected to the target machine.
 
+
To end the session, press Ctrl+A followed by Ctrl+X.
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====
  
Screen is able to connect to a serial port. It will connect to a standard 9600 speed port without options.
+
{{Pkg|screen}} is able to connect to a serial port. It will connect at 9600 baud by default:
  
 
  screen /dev/ttyS0
 
  screen /dev/ttyS0
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  screen /dev/ttyS0 115200
 
  screen /dev/ttyS0 115200
  
If needed, see the section "WINDOW TYPES" in the screen man page for details on setting other connection parameters.
 
  
 
====Serialclient====
 
====Serialclient====

Revision as of 05:49, 18 June 2014

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

GRUB2 and systemd

If you configure the serial console in GRUB2 systemd will create a getty listener on the same serial device as GRUB2 by default. So, this is the only configuration needed for Arch running with systemd. To make grub enable the serial console, open /etc/default/grub in an editor. Change the GRUB_CMDLINE_DEFAULT line to start the console on /dev/ttyS0. Note in the example below, we set two consoles up; one on tty0 and one on the serial port.

 GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,38400n8"

Now we've got to tell grub what command to start in order to enable the serial console:

 # Serial console
 GRUB_TERMINAL=serial
 GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"

Rebuild the grub.cfg file

 # grub-mkconfig -o /boot/grub/grub.cfg

After a reboot, getty will be listening on /dev/ttyS0, expecting 38400 baud, 8 data bits, no parity and one stop bit. When Arch boots, systemd will automatically start a getty session to listen on the same device with the same settings.

Without GRUB2, systemd only

Ignore this entire section if you have configured GRUB2 to listen on the serial interface. If you do not want GRUB2 to listen on the serial device, but only want getty listening after boot then follow these steps.

To start getty listening on /dev/ttyS0 use systemctl

 systemctl start getty@ttyS0.service

You can check to see the speed(s) getty is using with systemctl, but should be 38400 8N1

 systemctl status serial-getty@ttyS0.service

To have getty listening on /dev/ttyS0 every boot, enable the service for that specific port.

 systemctl enable serial-getty@ttyS0.service

Now, after a reboot, getty will be listening on device /dev/ttyS0 expecting 38400 baud, 8 data bits, no parity and one stop bit

GRUB v1 and No systemd

Edit the GRUB config file /boot/grub/menu.lst and add these lines to the general area of the configuration:

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

Add suitable console parameters (e.g. change the serial device name or baud rate if required) 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 /vmlinuz-linux root=/dev/md0 ro md=0,/dev/sda3,/dev/sdb3 vga=773 console=tty0 console=ttyS0,9600
Note: When the terminal --timeout=5 serial console line is added to your menu.lst grub configuration, 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. The lines will look like this upon boot:

 Press any key to continue.
Press any key to continue.
Press any key to continue.
Press any key to continue.
Press any key to continue.
Press any key to continue.
Press any key to continue.

Next, we have to edit /etc/inittab and add a new agetty line below the existing ones:

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

Edit /etc/securetty and add an entry for the the serial console, below the existing entries:

 ttyS0

Reboot.

Note: In all of the steps above, ttyS1 can also be used in case 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

minicom can be obtained from the official repositories. Start Minicom in setup mode:

minicom -s

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). Remove the modem Init and Reset strings, as we're 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.

Screen

screen is able to connect to a serial port. It will connect at 9600 baud by default:

screen /dev/ttyS0

A different baud rate (e.g. 115200) may be specified on the commmand line.

screen /dev/ttyS0 115200


Serialclient

Serialclient[1] is a client for serial connection in command line in your shell. Install it doing:

pacman -S ruby
gem install serialclient

Then, you can use like this:

serialclient -p /dev/ttyS0

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.

3. When the bootloader appears, select "Boot Arch Linux (<arch>)" and press tab to edit

4. Append console=ttyS0 and press enter

5. Systemd should now detect ttyS0 and spawn a serial getty on it, allowing you to proceed 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 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.