1. An environment variable enables a program interact with the operating system by helping the program know where to store temporary files, where to install files, where to look for settings etc. Environment variables ultimately create and manage the environment in which a program runs. Environment variables help programs know what directory to install files in, where to store temporary files, where to find user profile settings, and other things. It can be said that environment variables help to create and shape the environment of where a program runs.
Environment variables are typically name-value string pairs that are dynamic as they can change to reflect the setup of the computer system and can vary from system to system.
A shell alias is a short name that is used in a shell in place of a longer name (Negus, 2007). In recognizing the short name, the shell translates it into another longer command or name. The definition of a shell alias is done by substituting a string for the first token of a shell command. The shell aliases are normally placed in the ~/.bashrc startup files for the bash shell so that the files are available and accessible to all the interactive subshells.
For instance alias x = “exit” defined to exit the screen when x is entered at the console.
2. On a Linux/UNIX operating system, a run level is a predefined state that the operating system can be booted into as represented by a single digit integer ranging from 0 to 6 on a standard linux kernel (Keir and Channelle, 2009). The run level to which the linux OS boots can be changed by using a text editor to manually edit the /etc/inittab file. The run level can also be changed by using the command
where X is the integer value of the run level to be booted into. For instance,
telinit 5 boots the OS to the run level 5 for GUI interface.
REFERENCES
Keir, T. and Channelle, A. (2009). Beginning Ubuntu Linux from Novice to Professional (4th ed.), Apress. PDF. ISBN-13: 978-1-4302-2000-B
Negus, C. (2007). Linux Bible. Wiley Publishing, Inc. PDF. ISBN: 978-0-470-08279-9.
