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How To Fix “make: flex: Command not found” Error on Xubuntu

Ubuntu 19

When using Xubuntu, you may encounter the error message “make: flex: Command not found”. This error typically occurs when the flex package, a tool for generating scanners, is not installed in your system. This article will guide you on how to fix this issue step by step.

Quick Answer

To fix the "make: flex: Command not found" error on Xubuntu, you need to install the flex package. However, in some versions of Xubuntu, the flex package might not be available in the default repositories. In that case, you can update your package sources to use the old-releases repository and then install the flex package.

Understanding the Error

Before we dive into the solution, it’s important to understand what the error message means. The make command is a utility for building and maintaining groups of programs (and other types of files) from source code. flex is a tool for generating scanners: programs which recognize lexical patterns in text. When you see the error “make: flex: Command not found”, it means the make utility is trying to use flex, but it can’t find it because it’s not installed.

Solution: Installing the Flex Package

To resolve this error, you need to install the flex package. However, in some versions of Xubuntu, the flex package might not be available in the default repositories. Therefore, you may need to update your package sources to use the old-releases repository. Here’s how you can do it:

Step 1: Open Terminal

Open a terminal by pressing Ctrl+Alt+T. This will bring up the terminal window, where you can input commands.

Step 2: Switch to Root User

Run the command sudo -i to switch to the root user. The sudo command allows you to run programs with the security privileges of another user (by default, the superuser). The -i (simulate initial login) option runs the shell specified by the password database entry of the target user as a login shell.

Step 3: Edit sources.list File

Open the sources.list file in the nano text editor by running nano /etc/apt/sources.list. The nano command opens the nano text editor, and /etc/apt/sources.list is the file you want to edit. This file contains a list of repositories from which packages can be installed or updated.

Step 4: Replace the Contents of the File

Delete the contents of the file and replace them with the following lines:

deb http://old-releases.ubuntu.com/ubuntu/ utopic main restricted
deb-src http://old-releases.ubuntu.com/ubuntu/ utopic main restricted
deb http://old-releases.ubuntu.com/ubuntu/ utopic-updates main restricted
deb-src http://old-releases.ubuntu.com/ubuntu/ utopic-updates main restricted
deb http://old-releases.ubuntu.com/ubuntu/ utopic universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ utopic universe multiverse
deb http://old-releases.ubuntu.com/ubuntu utopic-security main restricted
deb-src http://old-releases.ubuntu.com/ubuntu utopic-security main restricted
deb http://old-releases.ubuntu.com/ubuntu/ utopic-backports main restricted universe multiverse

Step 5: Save and Exit the File

Save the file by pressing Ctrl+O, then exit nano by pressing Ctrl+X.

Step 6: Update the Package Lists

Run the command apt-get update to update the package lists. The apt-get command is a powerful command-line tool used to work with Ubuntu’s Advanced Packaging Tool (APT) performing such functions as installation of new software packages, upgrade of existing software packages, updating of the package list index, and even upgrading the entire Ubuntu system.

Step 7: Upgrade the Installed Packages

Run the command apt-get dist-upgrade to upgrade the installed packages. The dist-upgrade command intelligently handles changing dependencies with new versions of packages and will attempt to upgrade the most important packages at the expense of less important ones if necessary.

Step 8: Install the Flex Package

Finally, run the command apt-get install flex to install the flex package.

Conclusion

This should install flex and resolve the “flex: Command not found” error. However, please note that Xubuntu 14.10 has reached its End of Life and is no longer supported. It is recommended to upgrade to a supported release or perform a fresh installation. For more information on how to do this, you can visit the Xubuntu website.

By following these steps, you should be able to fix the “make: flex: Command not found” error on Xubuntu. If you encounter any issues, feel free to ask for help in the comments section below.

What is Xubuntu?

Xubuntu is an official flavor of the Ubuntu operating system that uses the Xfce desktop environment. It is designed to be lightweight and fast, making it a good choice for older or less powerful hardware.

How do I open a terminal in Xubuntu?

To open a terminal in Xubuntu, you can press Ctrl+Alt+T on your keyboard. This will bring up the terminal window where you can input commands.

What is the purpose of the `sudo` command?

The sudo command allows you to run programs with the security privileges of another user, typically the superuser. It is often used to perform administrative tasks or run commands that require elevated privileges.

What is the `sources.list` file?

The sources.list file is a configuration file in Ubuntu that contains a list of repositories from which packages can be installed or updated. It specifies the locations from which the package manager should retrieve packages.

What does the `apt-get update` command do?

The apt-get update command updates the package lists for upgrades and installations. It retrieves the latest information about available packages from the repositories specified in the sources.list file.

How can I upgrade the installed packages in Xubuntu?

To upgrade the installed packages in Xubuntu, you can use the apt-get dist-upgrade command. This command intelligently handles changing dependencies with new versions of packages and will attempt to upgrade the most important packages at the expense of less important ones if necessary.

What is the purpose of the `apt-get install` command?

The apt-get install command is used to install packages in Ubuntu. By specifying the name of the package after the command, you can install the package and its dependencies.

How can I update or upgrade Xubuntu to a supported release?

To update or upgrade Xubuntu to a supported release, you can use the do-release-upgrade command. This command initiates the upgrade process and guides you through the steps to upgrade to the latest version of Xubuntu.

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