cu Command in Linux

Introduction

In this guide, we will delve into the cu command, a valuable asset in Linux environments for creating remote connections and facilitating file transfers between different systems. We will cover the installation process for the cu command, demonstrate how to establish a connection, and illustrate how to transfer files between the local and remote machines. This tutorial provides an introduction to the cu command, details connection establishment, and offers practical examples of file transfers.

The cu command might require manual installation on certain distributions, as it's not always included in the default installation. It's also worth noting that while the cu command remains functional and utilized, more modern and feature-rich alternatives exist, such as screen or tmux, which might be preferable depending on the specific needs of the systemadmin.

Introduction to the cu Command

In this section, we will explore the cu command, short for "Call Up" or "Connect to". The cu command is a useful utility within Linux for setting up remote connections and moving files across systems. It enables connections to various systems, including mainframes, minicomputers, and other Linux/Unix based systems, via a serial line or modem.

Initially, let's verify if the cu command is already present on our system:

sudo apt-get update
sudo apt-get install -y cu

Example output:

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following NEW packages will be installed:
  cu
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 35.6 kB of archives.
After this operation, 112 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu jammy/main amd64 cu amd64 1.07-1 [35.6 kB]
Fetching and Extracting packages... Done
Setting up cu (1.07-1) ...

With the cu command now installed, we are ready to use it for connecting to remote systems.

Establishing a Connection Using the cu Command

In this part, we will focus on how to initiate a connection using the cu command. This command facilitates connections to remote systems through a serial line or modem.

To establish a connection, use the following syntax:

sudo cu -l /dev/ttyUSB0 -s 9600

Here, the -l option designates the serial device to utilize, while the -s option determines the baud rate. Adjustments to these options might be necessary based on your particular configuration.

Upon successful connection, a prompt will appear, indicating your connection to the remote system. At this point, you can interact with the remote system as if directly logged in.

To terminate the cu session, type ~. (tilde followed by a period) and then press Enter.

Example output:

Connected.
login:

Let's now try to set up a connection using the cu command.

Transferring Files with the cu Command

In this section, we will explore the process of transferring files utilizing the cu command. This command enables the sending and receiving of files between the local and remote systems.

To transfer a file from the local system to the remote system, execute these steps:

  1. Establish a connection to the remote system using the cu command:
sudo cu -l /dev/ttyUSB0 -s 9600
  1. With the connection active, input ~> followed by the filename to transmit the file:
~>example.txt

This action will start the file transfer sequence. The remote system will prompt you to initiate the file transfer.

  1. To proceed with the file transfer, simply press Enter on the local system. The file will be transmitted to the remote system.

Example output:

Connected.
~>example.txt
[remote system prompts]
[file transfer starts]

To retrieve a file from the remote system, take the following steps:

  1. Establish a connection to the remote system through the cu command.
  2. On the remote system, enter ~< followed by the filename to initiate the file transfer.
  3. On the local system, the file transfer will commence automatically. The file will be saved in the current directory.

Example output:

Connected.
~<example.txt
[file transfer starts]
[file saved on local system]

Now, let's practice transferring a file using the cu command.

Summary

In this guide, we first explored the cu command, a powerful utility in Linux for creating remote connections and transferring files. We covered how to determine if the cu command is installed and the steps for installing it if needed.

Then, we focused on establishing connections with the cu command. We explained the syntax, including the -l option for specifying the serial device and the -s option for setting the baud rate. We also described how to terminate a cu session using ~..

400+ Linux Commands