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Linux Terminal and Basic Usage

 

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Overview

In this section, you will access the Linux terminal through the debug UART interface and learn basic useful Linux commands. In this module you will:

  • Power on your Computer on Module.
  • Use a serial terminal to communicate with the embedded system.
  • Be introduced to the Linux command-line interface.

Note: We will access the module using the Serial Terminal, therefore the USB keyboard and video interface connected to the module will not be used in this section.

Step 1

Open a terminal in the host machine:


  • Host terminal

    Host terminal

Step 2

Add your user to dialout group:

sudo adduser user dialout

Warning: Change the user on the command above to your system username.

Warning: After the command it is necessary to reboot or logoff the system.

Step 3

Install a serial terminal emulator application in your host computer:

sudo apt-get install gtkterm

Step 4

Open GTKterm, you can do it from your distro menu or from the terminal:


  • Find GTKterm on menu

    Find GTKterm on menu

gtkterm

  • GTKterm window

    GTKterm window

Step 5

To start the serial application, the parameters must be correctly set. From GTKTerm menu, select configuration->port:


  • GTKterm configuration menu

    GTKterm configuration menu

From the configuration window, select the serial device that corresponds to your module:

Note: Generally the last device listed on Port combo box (/dev/ttyUSB0) is the device you want. But if you have more than one usb serial connected, there will be more options listed e.g. /dev/ttyUSB1, /dev/ttyUSB2 and etc... To find out which one is the serial port device that you must use, you can unplug the USB-Serial adapter --> close the configuration window --> open it again and find the new device listed.


  • GTKterm configuration select serial device port

    GTKterm configuration select serial device port

With the device selected we need to set the correct baud rate 115200:


  • GTKterm configuration set baud rate

    GTKterm configuration set baud rate

With this configuration click "Ok" button to connect:


  • GTKterm configuration seted click ok

    GTKterm configuration seted click ok

Step 5

Power-on the embedded system. Messages will immediately start to be printed in the serial terminal. When the messages stop, a login prompt will be the last content printed to the terminal. You can press Enter to refresh the login prompt if any message is printed after it.

Warning: To login, the default username is root and no password is required:


  • Login prompt

    Login prompt

Note: In some cases, it is needed to close or to reconnect to the serial port, you can do it by pressing F5 to connect/reconnect and F6 to close, or use the Control signals menu:


  • GTKterm Control signals

    GTKterm Control signals

Some modules will get a kernel panic error while updating from an image 2.7b3 or older to 2.74b4 or newer, it occurs because images 2.7b3 and older use EXT-3 for mounting the root file system, and starting with image 2.7b4, the root file system is mounted using EXT-4,. To solve this problem, power-cycle the system and enter U-Boot command line by pressing any key, then reload the default U-Boot environment and save it, as presented in the commands below:

env default -a
saveenv
boot

Warning: If you have custom U-Boot variables set, please make sure to copy them before proceeding, since this will erase any custom variables.

Step 6

If you are new to Linux or the command-line interface and want to learn some basic commands, please read this article