Difference between revisions of "Working with the serial console"

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[[Category:HOWTOs (English)]]
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[[Category:Other hardware]]
=Introduction=
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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).
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.
 
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 connecting the administering machine to the administrated machine, using a serial cable (9-pin connector cable).
+
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 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=
+
==Configuration==
  
 
===Configure console access on the target machine===
 
===Configure console access on the target machine===
  
1. Edit the grub.conf file:
+
====GRUB2 and systemd====
  
<pre>
+
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.
# vi /boot/grub/menu.lst
+
<br><br>
</pre>
+
Edit /etc/default/grub
 +
<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=====
 +
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>
 +
1. To start getty listening on /dev/ttyS0 use systemctl<br>
 +
{{ic|<nowiki>
 +
systemctl start getty@ttyS0.service
 +
</nowiki>}}
 +
<br><br>
 +
You can check to see the speed getty is useing with systemctl, but should be 38400 8N1<br>
 +
{{ic|<nowiki>
 +
systemctl status 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/getty@.service  /etc/systemd/system/getty.target.wants/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====
 +
 
 +
1. Edit the GRUB config file:
 +
 
 +
vi /boot/grub/menu.lst
 +
 
 +
Add these lines to the general area of the configuration:
 +
 
 +
{{ic|<nowiki>
 +
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:
 
Add the console parameters at the end of your current kernel line:
  
<pre>
+
{{ic|<nowiki>
console=ttyS0,9600
+
console=tty0 console=ttyS0,9600
</pre>
+
</nowiki>}}
  
 
For example, the kernel line should look something like this after modification:
 
For example, the kernel line should look something like this after modification:
  
<pre>
+
{{ic|<nowiki>
kernel /vmlinuz26 root=/dev/md0 ro md=0,/dev/sda3,/dev/sdb3 vga=773 console=ttyS0,9600
+
kernel /vmlinuz-linux root=/dev/md0 ro md=0,/dev/sda3,/dev/sdb3 vga=773 console=tty0 console=ttyS0,9600
</pre>
+
</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:}}
 +
 
 +
{{ic|
 +
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:  
 
2. Edit the inittab file:  
  
<pre>
+
vi /etc/inittab
# vi /etc/inittab
+
</pre>
+
  
Add a new agetty line below the existing ones :
+
Add a new agetty line below the existing ones:
  
<pre>
+
{{ic|
 
c0:2345:respawn:/sbin/agetty 9600 ttyS0 linux
 
c0:2345:respawn:/sbin/agetty 9600 ttyS0 linux
</pre>
+
}}
  
 
3. Edit the securetty file:
 
3. Edit the securetty file:
<pre>
 
# vi /etc/securetty
 
</pre>
 
  
Below the existing tty's add an entry for the the serial console:
+
vi /etc/securetty
<pre>
+
 
 +
Below the existing ttys, add an entry for the the serial console:
 +
 
 +
{{ic|
 
ttyS0
 
ttyS0
</pre>
+
}}
  
 
4. Reboot the machine
 
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.
+
{{note|In all of the steps above, ttyS1 can also be used in case your machine has more than one serial port.}}
  
=Making Connections=
+
==Making Connections==
  
 
===Connect using a terminal emulator program===
 
===Connect using a terminal emulator program===
Line 64: Line 126:
 
Perform these steps on the machine used to connect the remote console.
 
Perform these steps on the machine used to connect the remote console.
  
1. Install Minicom:
+
====Minicom====
  
<pre>
+
1. Install {{Pkg|Minicom}}:
# pacman -S minicom
+
 
</pre>
+
pacman -S minicom
  
 
2. Start Minicom in setup mode:
 
2. Start Minicom in setup mode:
  
<pre>
+
minicom -s
# minicom -s
+
</pre>
+
  
3. Using the textual navigation menu change the serial port settings to the following:
+
3. Using the textual navigation menu, change the serial port settings to the following:
  
<pre>
+
{{ic|
Serial Device: /dev/ttyS0
+
Serial Device: /dev/ttyS0<br>
 
Bps/Par/Bits: 9600 8N1
 
Bps/Par/Bits: 9600 8N1
</pre>
+
}}
  
Press Enter to exit the menus (pressing Esc will not save changes)
+
Press Enter to exit the menus (pressing Esc will not save changes).
  
 
4. Remove the modem Init and Reset strings:
 
4. Remove the modem Init and Reset strings:
  
Under the 'Modem and Dialing' menu delete the Init and Reset strings.
+
Under the 'Modem and Dialing' menu, delete the Init and Reset strings.
  
 
5. Save the setup:
 
5. Save the setup:
  
From the main menu, choose 'save setup as dfl'
+
From the main menu, choose 'save setup as dfl'.
  
 
6. Exit Minicom:
 
6. Exit Minicom:
  
From the main menu, choose 'Exit from Minicom'
+
From the main menu, choose 'Exit from Minicom'.
  
 
7. Connect to the target machine:
 
7. Connect to the target machine:
Line 101: Line 161:
 
While the serial cable is connected to the target machine, start the Minicom program:
 
While the serial cable is connected to the target machine, start the Minicom program:
  
<pre>
+
minicom
# minicom
+
</pre>
+
  
 
8. Exiting Minicom
 
8. Exiting Minicom
  
To finish the session press 'ctrl-A' and then 'X'.
+
To finish the session, press 'ctrl-A' and then 'X'.
  
On Windows machines, connect to the serial port using programs like Putty or Hyper Terminal.
+
====Screen====
  
=Installing Arch Linux using the serial console=
+
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.
 +
 
 +
====Serialclient====
 +
 
 +
Serialclient[https://github.com/flagos/serialclient] 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.
 
1. Connect to the target machine using the method described above.
Line 117: Line 194:
 
2. Boot the target machine using the Arch Linux installation CD.
 
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.
+
3. When the bootloader appears, select "Boot Arch Linux (<arch>)" and press tab to edit
 +
 
 +
4. Append {{ic|1=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')}}
  
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.
+
==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.

Revision as of 18:03, 28 November 2012

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.

Edit /etc/default/grub

1. Edit the GRUB_CMDLINE_DEFAULT="" line to start the console on /dev/ttyS0
GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,38400n8"

2. Add a serial console section
# Serial console
GRUB_TERMINAL=serial
GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"


3. Rebuild the grub.cfg file
grub-mkconfig > /boot/grub/grub.cfg

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

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.

1. To start getty listening on /dev/ttyS0 use systemctl
systemctl start getty@ttyS0.service

You can check to see the speed getty is useing with systemctl, but should be 38400 8N1
systemctl status getty@ttyS0.service

2. To have getty listening on /dev/ttyS0 every boot create this symlink ln -s /usr/lib/systemd/system/getty@.service /etc/systemd/system/getty.target.wants/getty@ttyS0.service

Now after reboot getty will be listening on device /dev/ttyS0 with settings 38400 8N1

GRUB v1 and No systemd

1. Edit the GRUB config 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 /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.

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 ttys, add an entry for the the serial console:

ttyS0

4. Reboot the machine

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

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.

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.