The shell is the default working environment for a Linux administrator. Whether you are setting up services or troubleshooting, mastering basic Linux tools is an essential prerequisite before attempting the RHCSA exam. Here is a comprehensive guide to the core tools and shell skills every system administrator must know.
Basic Shell Skills and Command Syntax Working effectively in the shell starts with understanding command syntax, which is typically divided into three parts: the command, its options, and its arguments. When you execute a command, the shell determines if it is an alias, an internal shell command, or an external command located in your $PATH variable.
To manipulate how these commands handle data, you should master I/O Redirection and Pipes:
- I/O Redirection: By default, standard output (STDOUT) and standard error (STDERR) display on your monitor, while standard input (STDIN) is fed from your keyboard. Using redirectors like
>,>>,<, and2>, you can reroute these streams to files or device files, such as/dev/nullto discard output. - Pipes: Using the pipe symbol (
|), you can catch the output of one command and immediately use it as the input for a second command, allowing you to chain utilities together flexibly.
To save time on the command line, leverage the Bash history and Bash completion. The shell automatically keeps track of your last 1,000 commands, which are saved to the .bash_history file when you log out. You can search this history by pressing Ctrl-r or execute a specific line number by typing !number. Additionally, pressing the Tab key will automatically complete commands, file names, and variables.
Editing Files with vim Because almost everything in Linux is configured through text files, knowing how to use a text editor is non-negotiable. While vi is universally available, vim (vi improved) is highly recommended as it provides helpful enhancements like syntax highlighting.
The most important concept to grasp in vim is its use of different modes, specifically command mode and input mode. You cannot type text in command mode; you must press i or a to enter input mode. Do not overwhelm yourself trying to memorize every vim command; simply focus on the essentials like dd to cut a line, yy to copy, p to paste, and :wq to write and quit.
Understanding the Shell Environment Your user environment relies on variables—fixed names assigned dynamic values, such as $LANG for language settings or $PATH for executable locations.
When a user logs in, this environment is constructed using a hierarchy of configuration files:
- /etc/profile: Processed for all users upon login.
- ~/.bash_profile: Used for user-specific login shell variables.
- ~/.bashrc: Used for user-specific subshell variables.
Administrators can also communicate with users during the login process using /etc/issue to display instructions before a user logs in, or /etc/motd (Message of the Day) to show information after a successful login.
Finding Help When You Need It No administrator memorizes every single command, which is why knowing how to find help is just as important as the commands themselves.
- –help: Appending this to almost any command will print a quick usage summary and a list of available options.
- man: This command opens detailed manual pages. If you don’t know the exact command you are looking for, you can use
man -koraproposto search themandbdatabase using keywords. - info: Some commands maintain their primary, in-depth documentation as Texinfo manuals, which can be browsed using the
infoorpinfocommands. - /usr/share/doc: This directory contains additional documentation and sometimes even sample configuration files for more complicated services.
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