Linux apt Tutorial: Install, Update and Remove Packages

On Linux you rarely download installers from websites. A package manager installs software from trusted repositories, along with everything it depends on, and keeps it up to date.

On Ubuntu and Debian, the tool is apt.

Update the list, then upgrade#

These two commands are often confused:

sudo apt update      # refresh the list of available versions
sudo apt upgrade     # install newer versions of what you have

apt update installs nothing. It only downloads the latest list, so always run it first.

Install a package#

Here we install cowsay, a small fun program. -y answers yes to the question, which is useful in scripts:

sudo apt-get install -y -qq cowsay > /dev/null 2>&1
/usr/games/cowsay "Installed with apt" 2>&1 | head -n 3

 ____________________
< Installed with apt >
 --------------------

Games like this one install to /usr/games. apt is designed for people, and apt-get is the older form, with stable output for scripts. They do the same job.

Search and inspect#

apt-cache search '^nginx$' | cut -c1-60
apt-cache policy cowsay | head -n 3
dpkg -l cowsay | tail -n 1 | awk '{print $1, $2, $3}'

nginx - small, powerful, scalable web/proxy server
cowsay:
  Installed: 3.03+dfsg2-8
  Candidate: 3.03+dfsg2-8
ii cowsay 3.03+dfsg2-8

Which files did it install?#

dpkg is the lower-level tool beneath apt:

dpkg -L cowsay | grep bin/
dpkg -S /usr/bin/grep

grep: /usr/bin/grep

-L lists a package's files. -S finds which package owns a file.

Remove a package#

sudo apt-get remove -y -qq cowsay > /dev/null 2>&1
dpkg -l cowsay 2>&1 | tail -n 1 | cut -c1-30

dpkg-query: no packages found

Other sources#

If a package is out of date in the official repositories, projects often offer their own repository. You add its signing key and a source file to /etc/apt/sources.list.d/. Only do this for sources you trust, because packages run as root when they install.

A .deb file downloaded by hand installs like this:

sudo apt install ./package.deb

Other package managers#

Common mistakes#

Practice#

dpkg -S /usr/bin/ls
dpkg -l | grep -c '^ii' | awk '{print ($1 > 100) ? "More than 100 packages" : "Fewer than 100"}'

coreutils: /usr/bin/ls
More than 100 packages

Key takeaway#

Next: Disk Space.