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Linux Terminal and Basic Usage


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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 usermod -a -G dialout user

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 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 6

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 Ext3 for mounting the root file system, and starting with image 2.7b4, the root file system is mounted using Ext4. 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

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 7

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