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Configuration Steps
- Connect a null modem cable between the system that will act as the console and the server. Refer to the Wikipedia article Null modem for details, including pin mapping.
- If the server's BIOS supports serial console, configure the BIOS for it. The details of this procedure are dependent on the BIOS vendor - refer to vendor documentation.
- Configure GRUB on the server to use the first serial port. In the file /boot/grub/menu.lst, comment out the color and gfxmenu lines and add the following lines:
serial --unit=0 --speed=115200
terminal --timeout=15 serial console
- Configure the kernel (and hypervisor) on the server to use the serial port. This configuration differs between Xen setups and non-Xen setups.
Non-Xen setup
In the file /boot/grub/menu.lst, add the following options to the kernel command line:
console=tty0 console=ttyS0,115200
Kernel messages will be written to both tty0 and ttyS0, but OS messages will only be written to ttyS0. OS messages go to the last console defined on the boot options line.
A sample /boot/grub/menu.lst file illustrating these changes:
#color white/blue black/light-gray
Xen setup
default 0
timeout 8
#gfxmenu (hd0,1)/boot/message
serial --unit=0 --speed=115200
terminal --timeout=15 serial console
title Linux ! SERIAL CONSOLE !
kernel (hd0,1)/boot/vmlinuz root=/dev/sda3 selinux=0 splash=0 resume=/dev/sda1 showopts elevator=cfq vga=791 console=tty0 console=ttyS0,115200
initrd (hd0,1)/boot/initrd
When Xen virtualization is used, both the Xen hypervisor and the Dom0 kernel need to be instructed to use the serial connection:
- Add console=vga,com1 com1=115200 to the parameters for the hypervisor.
- Add console=tty0 console=xvc0,115200 to the parameters for the Dom0 kernel.
A sample /boot/grub/menu.lst file illustrating these changes:
#color white/blue black/light-gray
default 0
timeout 8
#gfxmenu (hd1,0)/boot/message
serial --unit=0 --speed=115200
terminal --timeout=15 serial console
title Linux - Xen ! SERIAL CONSOLE !
kernel (hd0,1)/boot/xen.gz console=vga,com1 com1=115200
module (hd0,1)/boot/vmlinuz root=/dev/sda3 console=tty0 console=xvc0,115200
module (hd0,1)/boot/initrd
- Configure the server to allow logins over the serial connection. In the file /etc/inittab, add the following line.
S0:12345:respawn:/sbin/agetty -L 115200 console vt102
To allow single-user mode to work using the serial connection, additionally change the line
~~:S:respawn:/sbin/sulogin
in /etc/inittab to
~~:S:respawn:/sbin/sulogin /dev/console
NOTE: Single-user mode will only work on the serial console with this option. You will need to change it back, to run on the local console.
- Configure the serial port on the server as a secure port, so a login as root is possible on it without the need to log in as a regular user first.
Add lines
console
to the file /etc/securetty
ttyS0
xvc0
- Ensure the package screen is installed on the server; this will be used later on to send control sequences to it.
Society
Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers : Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism : The Iron Law of Oligarchy : Libertarian Philosophy
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Bulletin:
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History:
Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds : Larry Wall : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOS : Programming Languages History : PL/1 : Simula 67 : C : History of GCC development : Scripting Languages : Perl history : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history
Classic books:
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Last modified: March 12, 2019
