By configuring the physical serial port on a Linux server to listen for incoming connections, administrators can replace the traditional keyboard and monitor with a single serial cable. Now system administrators can manage physical servers with a serial cable attached to a laptop or a serial console server over a remote SSH session.
Over the years, serial consoles have lost favor to lights out management cards, such as
ipmi. However, in organizations where serial management is still prevalent, such as data centers with large networking environments, serial consoles are a viable alternative to LoM and KVM.
The first task is to determine the device file for the serial port. On Linux, the serial port is typically
Double check by looking at the
/dev/ttyS* files. Group ownership of physical serial ports may be
jemurray@myserver:~$ ls -al /dev/ttyS* crw-rw---- 1 root tty 4, 64 May 11 2019 /dev/ttyS0
Another option, is to examine the
/proc/tty/driver/serial file. Look for devices with
uart:16550A in them:
jemurray@myserver:~$ sudo cat /proc/tty/driver/serial serinfo:1.0 driver revision: 0: uart:16550A port:000003F8 irq:4 tx:1346 rx:172 brk:172 RTS|CTS|DTR|DSR 1: uart:16550A port:000002F8 irq:3 tx:0 rx:0 CTS
When in doubt, it does not hurt to try
/dev/ttyS0. If that does not work try the next
uart from the list above (ie.
The process that listens on the serial port is called
getty. It opens a tty port, prompts for a login name and invokes the /bin/login command. To enable
getty on the serial port, create and add the following to the
(For Ubuntu 9.10 to current)
# ttyS0 - getty # # This service maintains a getty on ttyS0 from the point the system is # started until it is shut down again. start on stopped rc or RUNLEVEL= stop on runlevel [!2345] respawn exec /sbin/getty -L 115200 ttyS0 vt102
(Ubuntu 6.x to 9.04)
# ttyS0 - getty # # This service maintains a getty on ttyS0 from the point the system is # started until it is shut down again. start on runlevel 1 start on runlevel 2 start on runlevel 3 start on runlevel 4 start on runlevel 5 stop on runlevel 0 stop on runlevel 6 respawn exec /sbin/getty 115200 ttyS0
Then start the
sudo start ttyS0
The following process will start:
root 3480 1 0 2020 ttyS0 00:00:00 /sbin/getty -L 115200 ttyS0 vt102
Connecting to Linux from a serial console:
Connect to port > 17 Ubuntu 20.04.4 LTS myserver ttyS0 myserver login:
Using a serial cable attached to laptop is dependent on the operating system, for macOS follow these instructions.