Tuesday, August 3, 2010

Linux Ubuntu Server 10.04 Chapter 2 Package Management

Linux Ubuntu Server 10.04 Chapter 2 is about Package Management


Ubuntu features a comprehensive package management system for the installation, upgrade, configuration, and removal of software. In addition to providing access to an organized base of over 24,000 software packages for your Ubuntu computer, the package management facilities QPPK7DA834B3 also feature dependency resolution capabilities and software update checking.

Several tools are available for interacting with Ubuntu's package management system, from simple
command-line utilities which may be easily automated by system administrators, to a simple graphical interface which is easy to use by those new to Ubuntu.


Ubuntu's package management system is derived from the same system used by the Debian GNU/
Linux distribution. The package files contain all of the necessary files, meta-data, and instructions to implement a particular functionality or software application on your Ubuntu computer.

Debian package files typically have the extension '.deb', and typically exist in repositories which are collections of packages found on various media, such as CD-ROM discs, or online. Packages are normally of the pre-compiled binary format; thus installation is quick and requires no compiling of software.

Many complex packages use the concept of dependencies. Dependencies are additional packages
required by the principal package in order to function properly. For example, the speech synthesis package Festival depends upon the package libasound2, which is a package supplying the ALSA sound library needed for audio playback. In order for Festival to function, it and all of its dependencies must be installed. The software management tools in Ubuntu will do this automatically

dpkg
dpkg is a package manager for Debian based systems. It can install, remove, and build packages, but unlike other package management system's it can not automatically download and install packages and their dependencies. This section covers using dpkg to manage locally installed packages:
• To list all packages installed on the system, from a terminal prompt enter:
dpkg -l

• Depending on the amount of packages on your system, this can generate a large amount of output.
Pipe the output through grep to see if a specific package is installed:
dpkg -l | grep apache2
Replace apache2 with any package name, part of a package name, or other regular expression.

• To list the files installed by a package, in this case the ufw package, enter:
dpkg -L ufw

• If you are not sure which package installed a file, dpkg -S may be able to tell you. For example:
dpkg -S /etc/host.conf
base-files: /etc/host.conf

The output shows that the /etc/host.conf belongs to the base-files package.

• You can install a local .deb file by entering:
sudo dpkg -i zip_2.32-1_i386.deb
Change zip_2.32-1_i386.deb to the actual file name of the local .deb file.

• Uninstalling a package can be accomplished by:
sudo dpkg -r zip

apt-get
The apt-get command is a powerful command-line tool used to work with Ubuntu's Advanced
Packaging Tool (APT) performing such functions as installation of new software packages, upgrade
of existing software packages, updating of the package list index, and even upgrading the entire
Ubuntu system.

Being a simple command-line tool, apt-get has numerous advantages over other package management
tools available in Ubuntu for server administrators. Some of these advantages include ease of use over simple terminal connections (SSH) and the ability to be used in system administration scripts, which can in turn be automated by the cron scheduling utility.
Some examples of popular uses for the apt-get utility:

• Install a Package: Installation of packages using the apt-get tool is quite simple. For example, to install the network scanner nmap, type the following:
sudo apt-get install nmap

• Remove a Package: Removal of a package or packages is also a straightforward and simple
process. To remove the nmap package installed in the previous example, type the following:
sudo apt-get remove nmap

Also, adding the --purge options to apt-get remove will remove the package configuration files as
well. This may or may not be the desired effect so use with caution.

• Update the Package Index: The APT package index is essentially a database of available
packages from the repositories defined in the /etc/apt/sources.list file. To update the local
package index with the latest changes made in repositories, type the following:
sudo apt-get update

• Upgrade Packages: Over time, updated versions of packages currently installed on your computer
may become available from the package repositories (for example security updates). To upgrade
your system, first update your package index as outlined above, and then type:
sudo apt-get upgrade

Automatic Updates
The unattended-upgrades package can be used to automatically install updated packages, and can be
configured to update all packages or just install security updates. First, install the package by entering
the following in a terminal:
sudo apt-get install unattended-upgrades

To configure unattended-upgrades, edit /etc/apt/apt.conf.d/50unattended-upgrades and adjust
the following to fit your needs:
Unattended-Upgrade::Allowed-Origins {
"Ubuntu lucid-security";
// "Ubuntu lucid-updates";
};
Certain packages can also be blacklisted and therefore will not be automatically updated. To blacklist a package, add it to the list:
Unattended-Upgrade::Package-Blacklist {
// "vim";
// "libc6";
// "libc6-dev";
// "libc6-i686";
};

To enable automatic updates, edit /etc/apt/apt.conf.d/10periodic and set the appropriate apt
configuration options:
APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Download-Upgradeable-Packages "1";
APT::Periodic::AutocleanInterval "7";
APT::Periodic::Unattended-Upgrade "1";

The above configuration updates the package list, downloads, and installs available upgrades every
day. The local download archive is cleaned every week.

Configuration APT
Configuration of the Advanced Packaging Tool (APT) system repositories is stored in the /etc/apt/
sources.list configuration file. An example of this file is referenced here, along with information on adding or removing repository references from the file.
Here is a simple example of a typical /etc/apt/sources.list file.
You may edit the file to enable repositories or disable them. For example, to disable the requirement
of inserting the Ubuntu CD-ROM whenever package operations occur, simply comment out the
appropriate line for the CD-ROM, which appears at the top of the file:
# no more prompting for CD-ROM please
# deb cdrom:[Ubuntu 10.04_Lucid_Lynx - Release i386 (20070419.1)]/ lucid main restricted

Repository
In addition to the officially supported package repositories available for Ubuntu, there exist additional community-maintained repositories which add thousands more potential packages for installation.

Two of the most popular are the Universe and Multiverse repositories. These repositories are not
officially supported by Ubuntu, but because they are maintained by the community they generally
provide packages which are safe for use with your Ubuntu computer.

By default, the Universe and Multiverse repositories are enabled but if you would like to disable them, edit /etc/apt/sources.list and comment the following lines:
deb http://archive.ubuntu.com/ubuntu lucid universe multiverse
deb-src http://archive.ubuntu.com/ubuntu lucid universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ lucid universe
deb-src http://us.archive.ubuntu.com/ubuntu/ lucid universe
deb http://us.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb http://us.archive.ubuntu.com/ubuntu/ lucid multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ lucid multiverse
deb http://us.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb http://security.ubuntu.com/ubuntu lucid-security universe
deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse

Ok. lets try that and see you at the next chapter.


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