Ubuntu Basic Tutorial: apt-get Command

Preface

The apt-get command is a package management tool in the Ubuntu system. It can be used to install and uninstall packages, upgrade packages, and upgrade the system to a new version. This article introduces the basic usage of the apt-get command. The demonstration environment is Ubuntu 18.04.

Basic syntax

Syntax format:

apt-get [options] command

Configuration Files:

The default configuration file for apt-get in the early days was /etc/apt/apt.conf, but this file does not exist by default in the current Ubuntu system.

If the /etc/apt/apt.conf file exists, apt-get will still read it. But the current design idea is to separate the configuration files and place them in the /etc/apt/apt.conf.d directory, which is easier to manage.

Common options:

-h, --help // View the help documentation -v, --version // View the version of apt-get -y // Respond to yes in scenarios that require confirmation
-s, --dry-run // Simulate execution and output results -d, --download-only // Download the package to the cache without installing it --only-upgrade // Update the current version of the package instead of installing a new version --no-upgrade // When executing the install command, do not install updates of the installed package -q, --quiet // Reduce output --purge // Delete the package configuration file with the remove command --reinstall // Reinstall the installed package or its new version

Common subcommands:

update

The update command is used to resynchronize the package index file. The configuration in the /etc/apt/sources.list file specifies the source of the package index file. After updating the package index file, you can get updated information and new package information of available packages. In this way, we have the following information locally: which versions of which software can be installed from where (source).

The update command should always be executed before installing or upgrading a package.

install

The install command is used to install or upgrade packages. Each package has a package name, not a fully qualified file name (for example, on a Debian system, the supplied argument is apt-utils, not apt-utils_1.6.1_amd64.deb). Packages that the installed package depends on will also be installed. The configuration file /etc/apt/sources.list contains the sources (servers) used to obtain packages. The install command can also be used to update specified packages.

upgrade

The upgrade command is used to install the latest versions of all packages currently installed on the system from the sources listed in /etc/apt/sources.list. In any case, currently installed packages will not be removed, and packages not yet installed will not be retrieved and installed. If a new version of a currently installed package cannot be upgraded without changing the installation state of another package, the current version will be retained. The update command must be executed in advance so that apt-get knows whether new versions of installed packages are available.

Note the difference between update and upgrade:

update is to update the software list, and upgrade is to update the software.

dist-upgrade

In addition to performing the upgrade function, dist-upgrade also intelligently handles changes in dependencies with new versions of packages. apt-get has a "smart" conflict resolution system that will try to upgrade the most important packages at the expense of less important ones if necessary. Therefore, the distr -upgrade command may remove some packages. Therefore, when updating the packages in the system, it is recommended to execute the following commands in sequence:

$ apt-get update
$ apt-get upgrade -y
$ apt-get dis-upgrade -y

remove

remove is similar to install, except that it removes packages instead of installing them. Note that removing a package using the remove command will leave its configuration files on the system.

purge

The purge command is similar to the remove command. The purge command deletes the package's configuration file at the same time as deleting the package.

autoremove

The autoremove command is used to remove automatically installed packages that were originally installed to satisfy the dependencies of other packages but are no longer needed.

download

The download command downloads the binary files of the specified package to the current directory. Note that it is a package file like *.deb.

clean

The clean command clears the packages retrieved from the local repository. It removes everything except the lock file from the /var/cache/apt/archives/ and /var/cache/apt/archives/partial/ directories.

autoclean

Similar to the clean command, the autoclean command clears the local repository of retrieved package files. The difference is that it only removes package files that can no longer be downloaded and are largely useless. This allows the cache to be maintained for long periods of time without growing out of control.

source

The source command downloads the source code for a package. By default, the latest available version of the source code is downloaded to the current directory.

changelog

The changelog command attempts to download and display a package's changelog.

Common usage

View Help Documentation

$ apt-get -h 

Update package index file

$ sudo apt-get update

Installing Packages

$ sudo apt-get install nginx

Respond with yes in situations where confirmation is required

Most packages require user interaction before installation and will continue installation after user confirmation. However, there is no way to interact with users in automated tasks. The -y option can be useful in scenarios like this, where it acts as if the user confirmed the installation:

$ sudo apt-get install -y nginx

Install updated packages in the system

$ sudo apt-get update
$ sudo apt-get upgrade -y
$ sudo apt-get dis-upgrade -y

Reinstall installed packages

If we think a package is not working properly, we can try to reinstall it by adding the --reinstall option to the install command. In addition, if the installed package has an update or new version, you can also use this method to upgrade the package to the latest version:

$ sudo apt-get install --reinstall curl 

Update the specified package

What is strange is that the update of the specified package is not done through the upgrade command, but with the install command. Note: it is the install command:

$ sudo apt-get install vim

Simulate execution of commands and output results

After applying the -s option, the command will not be actually executed, but it will simulate execution and output the results, such as the following example:

$ sudo apt-get update
$ sudo apt-get -s upgrade

By adding the -s option, the upgrade command will output the software to be updated but will not actually perform the upgrade.

Check the version of a package

You can view the versions of installed or upcoming packages by using the following command:

$ sudo apt-get -s install vim

Here is an example of an installed package:

Here is an example of an uninstalled package:

Install a specific version of the package

Note that this refers to the version number of the package:

$ sudo apt-get install tree=1.7.0-5

Download the package to the cache without installing it

The option -d, --download-only tells the command to only download the packages to the cache without installing them. It is mainly used in scenarios where downloading packages and installing packages are separated, such as the system's default automatic update:

$ sudo apt-get install -d nginx
$ sudo apt-get upgrade -d
$ sudo apt-get dist-upgrade -d

Removing a Package

The feature of the remove command is that it only deletes program files and retains related configuration files:

$ sudo apt-get remove vim

If you want to completely remove the package, you can use the purge command, which will delete both the program files and its configuration files:

$ sudo apt-get purge vim

The autoremove command is used to remove automatically installed packages that were originally installed to satisfy the dependencies of other packages but are no longer needed. Therefore it is a good idea to run autoremove after deleting the package:

$ sudo apt-get autoremvoe

Clear the cached package installation files in the system

The process of installing a package actually downloads the package installation file to the cache directory first, and then performs the installation. Over time, there will be a large number of useless package installation files in the system. The clean command can clear these cached package installation files:

$ sudo apt-get clean

The clean command removes everything except the lock file from the /var/cache/apt/archives/ and /var/cache/apt/archives/partial/ directories.

The autoclean command is similar to the clean command. The difference is that it only removes package files that can no longer be downloaded and are largely useless. This allows the cache to be maintained for long periods of time without growing out of control:

$ sudo apt-get autoclean

Using the --purge option when executing the remove command is equivalent to executing the purge command:

$ sudo apt-get remove --purge vim

Use the --autoremove option when executing the install/remove command to remove useless dependency packages at the same time, similar to executing the autoremove command again after executing the install/remove command:

$ sudo apt-get remove --autoremove vim

Display more detailed version information when executing install/upgrade commands

By using the -V option, you can let the install/upgrade command output the specific version of the package. The following is the default output:

$ sudo apt-get upgrade -s 

Here is the output after adding the -V option:

$ sudo apt-get upgrade -V -s 

Reduce output

Now that you can increase the verbose output, you can also use the -q option to reduce the output:

$ sudo apt-get install -q curl
$ sudo apt-get install -q=2 curl

View the change log of an installed package

You can use the changelog command to view the update record of the package:

$ apt-get changelog tree 

Download the source code of the package

The apt-get source command is used to download the source code of a package. To make the apt-get source command work, you need to update the /etc/apt/sources.list file and add the deb-src configuration, which is actually to cancel the originally commented-out line starting with deb-src. On the desktop version of the system, you can also do the same thing through the "Software & Updates" UI, in the "Ubuntu Software" tab, select the "Source code" item:

Now execute the apt-get source command and specify the package name to download the source code of the package:

$ apt-get source tree 

Check the version of apt-get

$ apt-get -v 

What is displayed here is actually apt, which is so weird! Next:

It turns out that the functions of apt-get, apt-cache and apt-config are all provided by the apt command.

View the system update history

The log file /var/log/apt/history.log records the system's update history. It can be used to view all installation, upgrade, and deletion records executed by the apt command:

$ less /var/log/apt/history.log

refer to:

apt-get man page

apt.conf man page

Summarize

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