Occasionally there are software patches and updates that are released for operating systems. The patches are reliable and are predictable and can be trusted to be appropriate. In order to receive the update, the computer must have an active internet connection. The command to issue that will update the operating system and repositories with the most recent updates is:

sudo apt-get update

The command to upgrade all of the currently installed software packages is:

sudo apt-get upgrade

Periodically, the distribution operating system will go through a significant upgrade. On an Long Term Support (LTS) version, this distribution period could be every 5 years. On systems with more bleeding edge technologies, the release cycles can be as often as every 6 months. Distribution upgrades bring major changes with many unknown results. It is important to make back up copies of all configuration files and any desired documents prior to beginning a distribution upgrade. The command to issue to execute a distribution upgrade is:

sudo apt-get install dist-upgrade

Many Linux distributions maintain a large variety and quantity of software packages. The packages are maintained in repositories that may be similar to an app store. Many times the version of software is not the most current version, however, the repositories generally maintain versions that are known to be stable for use. The command to install a popular word processing and spreadsheet software program, LibreOffice from default the software repositories is:

sudo apt-get install libreoffice

It is always prudent to run the update command after installing new software. This may fix any outstanding dependencies that may exist. There are times that software is found online, and is outside of a repository. Always use extreme caution with downloading software outside of normal repository systems. One common place to find such software is: www.sourceforge.net. This a well reputed open source software storage location. To download software from an file transfer protocol (ftp) server or other online location, first change directories to the desired download location. The /home/user/Downloads directory is a common location to put software to be installed. After navigating to the desired directory, issue the following command to download the file:

wget www.website.com/filename

After the file is downloaded, the file may need to checked for accuracy. This check is done to ensure that the entire file was downloaded correctly and also to ensure that you download a file that has not been altered. Some download locations will provide a checksum on their files. This checksum can be conducted on the file that you downloaded and compared to the checksum provided by the author. This checksum is sometimes called a hash. The most common hash is the MD5 hash algorithm, though the MD5 is still highly regarded, there are hashes that have been recognized to be more secure. These include the SHA1 and the SHA2 algorithms. Users can run the algorithim based on what the author provides. The command to run an MD5 hash is:

md5sum filename

The command to run the SHA1 hash is:

sha1sum filename

Once the file has been authenticated, the file can be moved to a more appropriate locaton to be installed. A common location to install software is: /usr/local/src
Due to the large size of some files, authors will compress files using any number of compression methods. The most common compression method in Windows is: .zip. In Linux, a compressed file is sometimes refered to as a tarball. The tarball must be "un-tarred" before it can be used. In linux the most common compression method are:
.tar.gz
and
.tar.bz2
After moving the tarball file to the directory in which you desire the software to be installed, the command to untar a .gz tarball is:

sudo tar -xjvf filename.tar.gz

The command to untar a .bz2 tarball is:

sudo tar -xjvf filename.tar.bz2

Once the file is untarred, look through the directory for a README file. Many times this will give instructions on how to further install some software packages. For example, there is an encryption software package that is called truecrypt. The most recent version was: trurcrypt-7.1a-setup-x64 Once the software is ready to be installed, run the following script: ./truecrypt-7.1a-setup-x64 Other software packages may require the following commands:

./install

make

make install

Another type of software package is refered to as a Debian package. These files can be recognized by their .deb suffix. The command to install a debian package is:

dpkg -i filename.deb

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