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Package management

Workflow

What is a package manager?

Modern operating systems use package managers to take care of the installation, maintenance and removal of software. On Windows this is Windows Installer (formerly Microsoft Installer). On Linux there are two popular package managers:

  • APT (used by Debian, Ubuntu)
  • RPM (RedHat, CentOS, Fedora, SuSe)

Specific commands for each system vary, but at their core they all provide the same functionality:

  • Install and uninstall packages
  • Upgrade packages
  • Install packages from a central repository
  • Search for information on installed packages and files

RPM and yum (RedHat, CentOS, Fedora, Scientific Linux)

In the following examples, we will be using dstat as the package we will be manipulating. The process however applies to any software you may want to install.

Yum provides a wrapper around RPM, which can be used to search for, and install packages from multiple package repositories. It also resolves dependencies, so that if a package has prerequisites, they will be installed at the same time.

If your Linux distribution uses RPM and yum, you can search for packages by running:

user@opsschool ~$ yum search dstat
======================== N/S Matched: dstat =========================
dstat.noarch : Versatile resource statistics tool

Installing packages

You can install a package using yum, by running:

root@opsschool ~# yum install dstat

=============================================================================
 Package        Arch            Version              Repository         Size
=============================================================================
Installing:
 dstat          noarch          0.7.0-1.el6          CentOS-6          144 k

Transaction Summary
=============================================================================
Install       1 Package(s)

Total download size: 144 k
Installed size: 660 k
Is this ok [y/N]:

If you have a downloaded RPM file, you can also install the package directly with the rpm command:

root@opsschool ~# rpm -i dstat-0.7.0-1.el6.noarch.rpm

Upgrading packages

RPM and yum both make it easy to upgrade existing packages, too. Over time, new packages may be added to the yum repositories that are configured on your system, or you may have a newer RPM for an already installed package.

To upgrade a package using yum, when a newer package is available, simply ask yum to install it again:

root@opsschool ~# yum install dstat

To upgrade all packages that have newer versions available, run:

root@opsschool ~# yum upgrade

To upgrade a package with an RPM file, run:

root@opsschool ~# rpm -Uvh dstat-0.7.1-1.el6.noarch.rpm

Uninstalling packages

To uninstall a package using yum, run:

root@opsschool ~# yum remove dstat

Similarly, you can uninstall a package with rpm:

root@opsschool ~# rpm -e dstat

Cleaning the RPM database

You can clean the RPM database, forcing it to refresh package metadata from its sources on next install or upgrade operation.

root@opsschool ~# yum clean all

Querying the RPM database

Occasionally you will want to find out specific information regarding installed packages. The -q option to the rpm command comes in handy here. Let's take a look at a few examples:

One common task is to see if you have a package installed. The -qa option by itself will list ALL installed packages. You can also ask it to list specific packages if they are installed:

user@opsschool ~$ rpm -qa dstat
dstat-0.7.0-1.el6.noarch

Now let's say we want to list all of the files installed by a package. The -ql option is the one to use:

user@opsschool ~$ rpm -ql dstat
/usr/bin/dstat
/usr/share/doc/dstat-0.7.0
/usr/share/doc/dstat-0.7.0/AUTHORS
/usr/share/doc/dstat-0.7.0/COPYING
/usr/share/doc/dstat-0.7.0/ChangeLog
...

We can also do the reverse of the previous operation. If we have a file, and want to known which package it belongs to:

user@opsschool ~$ rpm -qf /usr/bin/dstat
dstat-0.7.0-1.el6.noarch

Creating packages

.. todo:: Mention spec files and roughly how RPMs are put together.

.. todo:: Then introduce FPM and tell them not to bother with spec files yet.

There are two todos here.

dpkg and APT (Debian, Ubuntu)

In the following examples, we will be using dstat as the package we will be manipulating. The process however applies to any software you may want to install.

APT provides a wrapper around dpkg, which can be used to search for, and install packages from multiple package repositories.

If your Linux distribution uses dpkg and APT, you can search for packages by running:

user@opsschool ~$ apt-cache search dstat
dstat - versatile resource statistics tool

Note

In the following sections, we will be describing use of APT through the traditional commands of apt-get and apt-cache. However, modern systems may ship with an additional command apt which (generally) combines the functionality of both of the above commands. If your system supports apt by itself, it is recommended to use that, as it is a bit more user friendly.

Installing packages

You can install a package through apt, by running:

root@opsschool ~# apt-get install dstat

The following NEW packages will be installed:
  dstat
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/79.3 kB of archives.
After this operation, 351 kB of additional disk space will be used.
Selecting previously unselected package dstat.
(Reading database ... 124189 files and directories currently installed.)
Unpacking dstat (from .../archives/dstat_0.7.2-3_all.deb) ...
Processing triggers for man-db ...
Setting up dstat (0.7.2-3) ...

If you have a downloaded DEB file, you can also install the package directly with the dpkg command:

root@opsschool ~# dpkg -i dstat_0.7.2-3_all.deb

Upgrading packages

dpkg and APT both make it easy to upgrade existing packages, too. Over time, new packages may be added to the apt repositories that are configured on your system, or you may have a newer deb for an already installed package.

In order to retrieve the updated package lists, first run:

root@opsschool ~# apt-get update

To upgrade a single package using apt, when a newer package is available, simply ask apt to install it again:

root@opsschool ~# apt-get install dstat

To upgrade all packages at once, run:

root@opsschool ~# apt-get upgrade

To upgrade a package with an deb file, run:

root@opsschool ~# dpkg -i dstat_0.7.2-3_all.deb

Uninstalling packages

To uninstall a package using apt, run:

root@opsschool ~# apt-get remove dstat

Similarly, you can uninstall a package with dpkg:

root@opsschool ~# dpkg -r dstat

With APT and dpkg, removing a package still leaves behind any configuration files, in case you wish to reinstall the package again later. To fully delete packages and their configuration files, you need to purge:

root@opsschool ~# apt-get purge dstat

or:

root@opsschool ~# apt-get --purge remove dstat

or:

root@opsschool ~# dpkg -P dstat

Querying the dpkg database

Occasionally you will want to find out specific information regarding installed packages. The dpkg-query command has many options to help. Let's take a look at a few examples:

One common task is to see if you have a package installed. The -l option by itself will list ALL installed packages. You can also ask it to list specific packages if they are installed:

user@opsschool ~$ dpkg-query -l dstat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-==================================
ii  dstat          0.7.2-3      all          versatile resource statistics tool

Now let's say we want to list all of the files installed by a package. The -L option is the one to use:

user@opsschool ~$ dpkg-query -L dstat
/.
/usr
/usr/bin
/usr/bin/dstat
/usr/share
...

We can also do the reverse of the previous operation. If we have a file, and want to know to which package it belongs:

user@opsschool ~$ dpkg-query -S /usr/bin/dstat
dstat: /usr/bin/dstat