5 Linux / Unix Commands For Connecting To The Serial Console

Posted on in Categories Command Line Hacks, Hardware, Networking last updated August 9, 2016

Most embedded Linux / BSD systems such as routers, servers and nas devices comes with console interface (serial port with RS-232). BIOS can uses this, and after boot BIOS screen I/O is redirected so that you can use the device. RS-232 is also used for communicating to headless server, where no monitor or keyboard is installed, during boot when operating system is not running yet and therefore no network connection is possible. You need to use a serial cable between your computer and embedded system or server. In this post I will cover five conman utilities used for serial communication under Linux / Unix / *BSD and Mac OS X.

Find out information about your serial ports

Type the following dmesg command:
$ dmesg | egrep --color 'serial|ttyS'
Sample outputs:

[    1.245258] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[    1.265727] serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
[    1.286713] 00:07: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[    1.307321] 00:08: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A

You can use setserial command which is designed to set and/or report the configuration information associated with a serial port:
$ setserial -g /dev/ttyS[0123]
Sample outputs:

/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 3
/dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4
/dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3

#1 cu command

The cu command is used to call up another system and act as a dial in terminal. cu command is installed on many Unix like systems including OpenBSD/AIX/Solaris and so on. You can use it as follows:

cu -l /dev/device -s baud-rate-speed

In this example, I’m using /dev/ttyS0 with 19200 baud-rate:

cu -l /dev/ttyS0 -s 19200

Sample outputs:

Fig.01: cu command in action
Fig.01: cu command in action

To exit enter tilde dot (~.).

#2 screen command

Use the screen command as follows:
$ screen /dev/device baud-rate
$ screen /dev/ttyS0 19200
$ screen /dev/ttySUSB0 19200,cs8
Sample outputs:

Fig.02: serial command connected to my personal router powered by dd-wrt
Fig.02: serial command connected to my personal router powered by dd-wrt

#3 minicom command

minicom command is a communication program which somewhat resembles the shareware program TELIX from old good MS-DOS days. Type minicom to connect:
$ minicom
Sample outputs:

Fig.03: minicom connected to my m0n0wall embedded firewall
Fig.03: minicom connected to my m0n0wall embedded firewall

See how to install and use minicom under Linux operating systems.

#4 putty command

PuTTY is a free and open source gui X based terminal emulator client for the SSH, Telnet, rlogin, and raw TCP computing protocols and as a serial console client. It works under Linux, Unix, Mac OS X, MS-Windows and few other operating systems. See how to configure and use putty for cisco routers:

Fig.04: putty in action
Fig.04: putty in action

You can use the apt-get or yum command to install putty:
$ sudo apt-get install putty

#5 tip command

The tip command is used as a serial terminal. tip command can be found under AIX/HP-UX/Solairs/*BSD/Linux operating systems. The syntax is:
tip -19200 device
tip -19200 s0
tip -19200 ttys0

How do I redirect Linux / BSD console output over serial port?

See our previous howtos about setting and redirecting console output over serial port:

  1. OpenBSD: Set a serial console
  2. FreeBSD: Set a serial console
  3. Debian / Ubuntu Linux: Set a serial console
  4. RHEL / CentOS / Fedora Linux: Set a serial console

You can also use the KVM over IP client as described here for serial console redirection over IP (LAN/WAN).

A note about MS-Windows users

If you forced to use MS-Windows, try the following free and open source serial communication programs:

Check out related media

Here is a quick demo of my Soekris router running monowall embedded version. The minicom is used to connect to the device and access BIOS and boot the system:

(Video.01: minicom in action)

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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15 comment

  2. NinjaTerm is another serial terminal option. It is a graphical program that works on Windows/MacOS/Linux. It has features such as ANSI esc. code support, filtering and timestamping.

    DISCLAIMER: I am the author.

  4. May I suggest replacing “dmesg | egrep –color ‘serial|ttyS'” with “dmesg | egrep –color ‘serial|ttyS|ttyU'”… I used this to also display my USB-rs232 dongle info.

  7. Hi, gr8 article!
    I’m looking for a way to communicate over RS232 with non-ASCII as well.
    How can I send non-ASCII character to serial?
    how can i read a non-ASCII character form serial?

    where can I get setserial? All links on the web seem to be dead.
    Does anyone have a copy of that program?

    1. Use your package manager to install setserial.

      All links on the web seem to be dead.

      What do you mean by all links are dead? Are you talking about links on our domain cyberciti.biz or external resources?

  8. Python-serial have a utility named miniterm.py. I like it because it have a full support for colors and UTF and is very tiny if you have python.

    leonardo@betty:~$ miniterm.py --help
Usage: miniterm.py [options] [port [baudrate]]

Miniterm - A simple terminal program for the serial port.

Options:
  -h, --help            show this help message and exit
  -p PORT, --port=PORT  port, a number (default 0) or a device name
                        (deprecated option)
  -b BAUDRATE, --baud=BAUDRATE
                        set baud rate, default 9600
  --parity=PARITY       set parity, one of [N, E, O, S, M], default=N
  -e, --echo            enable local echo (default off)
  --rtscts              enable RTS/CTS flow control (default off)
  --xonxoff             enable software flow control (default off)
  --cr                  do not send CR+LF, send CR only
  --lf                  do not send CR+LF, send LF only
  -D, --debug           debug received data (escape non-printable chars)
                        --debug can be given multiple times: 0: just print
                        what is received 1: escape non-printable characters,
                        do newlines as unusual 2: escape non-printable
                        characters, newlines too 3: hex dump everything
  --rts=RTS_STATE       set initial RTS line state (possible values: 0, 1)
  --dtr=DTR_STATE       set initial DTR line state (possible values: 0, 1)
  -q, --quiet           suppress non error messages
  --exit-char=EXIT_CHAR
                        ASCII code of special character that is used to exit
                        the application
  --menu-char=MENU_CHAR
                        ASCII code of special character that is used to
                        control miniterm (menu)

  10. Be advised, that screen’s serial terminal support is optional and some Linux distros disable it, citing redundancy issues. Namely Debian and Ubuntu.

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