Package Management Functions in Linux
As most UKFast servers are either CentOS/Red Hat or Ubuntu/Debian, this article will only cover two of the most popular Linux package managers, yum and apt.
yum
Installing Packages
To install a package in yum, the following syntax can be used:
yum install $PACKAGE_NAME
This will search the currently installed repositories for a package with that name and install it if it’s found.
If the package you’re looking for isn’t found, then you may have to install an additional repository that does provide it.
A common additional repository is epel (Extra Packages for Enterprise Linux).
On CentOS, this can itself be installed using yum:
yum install epel-release
If you’re using official Red Hat Enterprise Linux, you will need to download the RPM from the EPEL site and install it manually, as well as enabling packages in the ‘optional’ RHEL repo. More instructions can be found here
With this installed, we can then install additional utilities on our server that were previously unavailable:
yum install htop
Updating Packages
In all these examples, the update command will be used rather than upgrade. Both commands look to perform the same function, but upgrade will remove packages that it classifies as obsolete as part of the upgrade process. If you’re confident in what you’re removing or drive space is at a premium then this option can be used instead.
The update syntax for yum is similar to the install syntax:
yum update $PACKAGE_NAME
If it’s just one package that needs to be updated then the above syntax is fine, for example:
yum update httpd
If you’re looking to update all the packages on your server, simply run the command without a package name:
yum update
Take care when updating all the packages on a server, this isn’t something that should be done blindly. Review the packages that are going to update before accepting it. Failure to review package updates could result in you running a higher version of something critical (such as PHP) than your code supports.
Extra functions
You can always run a number of checks with yum before either installing or updating an application.
If you wish to check whether a package is available on your system, you can always run a search in yum. This will print out all the packages that match your search:
yum search $QUERY
An example of this, including a snippet of the output, is as follows:
yum search php
...
=============================== N/S matched: php ===============================
php.x86_64 : PHP scripting language for creating dynamic web sites
php-Assetic.noarch : Asset Management for PHP
php-EasyRdf.noarch : A PHP library designed to make it easy to consume and
: produce RDF
...
If the package exists on your system, you can pull additional information on it, including what version of the package is available to you.
This will also show you information on an updated version of the package you’ve got. It also highlights the package’s name in a different collour based on its status.
Red: Obsolete yellow: Installed from another source bold white: Currently installed white: Available, but not installed blue: Update
yum info $PACKAGE_NAME
Here is an example, including a snippet of the output, without colour highlights:
yum info php70w
...
Installed Packages
Name : **php70w**
Arch : x86_64
Version : 7.0.11
Release : 1.w7
Size : 9.0 M
Repo : installed
From repo : webtatic
...
Available Packages
Name : **php70w**
Arch : x86_64
Version : 7.0.12
Release : 1.w7
Size : 2.8 M
Repo : webtatic/x86_64
...
Yum also has great history features that allow you to examine your previous installations and roll them back if necessary.
To view the history of your yum transactions, run yum history list, which will output something like:
[root@7dd0ac475f64 /]# yum history
Loaded plugins: fastestmirror, ovl
ID | Command line | Date and time | Action(s) | Altered
-------------------------------------------------------------------------------
4 | groupinstall development | 2017-10-24 09:20 | I, U | 109 EE
3 | install vim-enhanced | 2017-10-24 09:19 | Install | 33 EE
2 | -y remove bind-libs bind | 2017-08-01 17:24 | Erase | 35 E<
1 | | 2017-08-01 17:23 | Install | 178 >
history list
In the above example, if you had finished with the packaged you installed in transaction 4, you could then remove those by running yum history undo 4. If you wished to rollback your server to transaction 2, you could run yum history rollback 2 which would remove packages installed in transactions 3 and 4.
You can get more information about this powerful feature by running yum help history or viewing the yum man page (man yum).
apt
Installing Packages
To install a package with apt you should first update the apt cache, then install your desired package:
apt-get update
apt-get install $PACKAGE_NAME
Updating the cache first is important as this will ensure you get the latest available packages and security updates.
Updating Packages
As with installing, you should ensure your apt cache is up to date so you get the latest software updates and security patches.
apt-get update
apt-get upgrade
or
aptitude update
aptitude upgrade
This will pull in all available updates for your system. Sometimes you may find that packages have been held back (usually Linux kernel updates). These can be pulled in by running a dist-upgrade.
apt-get dist-upgrade
or
aptitude full-upgrade
If you wish to view which version you’re upgrading to and from you can always enable verbosity with the ‘-V’ option
apt-get -V upgrade|dist-upgrade
or
aptitude -V upgrade|full-upgrade
Take care when updating all packages on a server. This is not something which should be done blindly. Review the packages that are going be updated before accepting the upgrade. If you fail to review the packages you may end up installing a new major version of a package which is not going to be compatible with your code, e.g. MySQL or PHP.
Extra Functions
With apt, there are 2 ways to perform a search for packages, but viewing package info applies the same to both methods.
apt-cache search $QUERY
This will display all packages that have matches based on name, summary, and full description.
If you only want package and summary searches, you can run the following:
aptitude search $QUERY
Here are some examples and their outputs:
apt-cache search php
...
adminer - Web-based database administration tool
air-quality-sensor - user space driver for AppliedSensor's Indoor Air Monitor
ampache - web-based audio file management system
ampache-common - web-based audio file management system common files
ampache-themes - Themes for Ampache
aolserver4-doc - AOL web server version 4 - documentation
...
aptitude search php
...
p cakephp - MVC rapid application development framework for PHP
p cakephp-instaweb - Development webserver for CakePHP applications
p cakephp-scripts - MVC rapid application development framework for PHP (scripts)
p dh-make-php - Creates Debian source packages for PHP PEAR and PECL extensions
p dh-php5 - debhelper add-on to handle PHP PECL extensions
...
With aptitude searches, they show information about the installation status of a package.
- ‘p’ shows that the package is available, but not installed.
- ‘v’ shows that this is a virtual package, i.e. it’s provided by another package.
- ‘i’ shows that the package is installed.
- ‘c’ shows that the package was removed, but the configuration still remains
If an ‘A’ is visible, it shows that this was automatically installed as a dependency to another package.
After searching for a package you can get more information with the following command:
apt-cache show $PACKAGE_NAME
or
aptitude show $PACKAGE_NAME
Here is an example, and a snippet of the output:
apt-cache show linux-image-amd64
or
aptitude show linux-image-amd64
...
Package: linux-image-amd64
State: installed
Automatically installed: no
Version: 3.16+63
Priority: optional
Section: kernel
...
This will tell you additional information, such as what packages it depends on, and which packages it will conflict with, along with a description of what the package does.
