What does sudo apt update on Linux do?

sudo apt update is a command used in Debian-based Linux distributions like Ubuntu to update the package information on your system. Here's what it does:

  1. Refreshes Package Lists: When you run sudo apt update, your system contacts the package repositories specified in your /etc/apt/sources.list file. These repositories are servers that contain a list of available software packages for your distribution.

  2. Downloads Package Information: The command downloads the latest package information from these repositories. This information includes details about available packages, their versions, dependencies, and their current status.

  3. Updates Local Cache: This downloaded package information is stored locally on your system in the /var/lib/apt/lists/ directory. This cache is used by the package manager (apt) to quickly search for and retrieve packages when you install or update software.

By running sudo apt update, you ensure your system has the most up-to-date information about available packages and their versions. This is essential for several reasons:

  • Security: It allows you to receive security updates promptly. When security vulnerabilities are discovered in software, updates are released to patch those vulnerabilities. Running sudo apt update ensures that your system knows about these updates and can install them when you run sudo apt upgrade.

  • Software Installation: Before you install new software or update existing packages, you should update the package information. This ensures that you're working with the latest versions of packages and their dependencies.

  • Dependency Resolution: apt uses the package information to resolve dependencies. When you want to install or upgrade a package, it checks this information to determine which other packages are required and whether they're available.


sudo apt update is a crucial step in maintaining a well-functioning and secure Linux system. It doesn't install any updates itself but ensures your system is aware of the latest package versions and their availability, which you can then install using sudo apt upgrade or install new software with sudo apt install.