Chapter - 1: Basics of linux | 0x-s0M3n4th's Blog

Radhe Radhe, I will be listing out the things we will be covering thtroughout this chapter.

List of Contents :

Basics of Linux file structure where we will see different types of folders, which contain different information.
Directory listing command and it’s sub types -> mainly we will see ls and it’s different options.
Understanding directoy and how we can navigate inside any directory.
A small touch on terminal devices.
Basics of system uptime options.
How we can determine certain path of a command using commands itself.
Understanding information about systems and how to check them.
Basic CPU information.
How to use different helping manuals to get help when we will be getting stuck in certain situations.

Note

If you already know all of the above feel free to skip this chapter or to revise you can do the practice lab section directly to test your skills. There is a cheat sheet section included for each chapter, feel free to reference that as a companion. HAVE FUN and KEEP LEARNING.

Linux Directories

The default display manager in RHEL 9 is called GDM(GNOME Display Manager) Linux Directory Structure: Linux files are organized logically in a hierarchy for ease of administration and recognition. This organization is maintained in hundreds of directories located in larger containers called file systems. Red Hat Enterprise Linux follows the Filesystem Hierarchy Standard (FHS) for file organization, which describes names, locations, and permissions for many file types and directories. The Linux directory structure is analogous to an inverted tree, where the top of the tree is the root of the directory, tree branches are subdirectories, and leaves are files. Path example: /etc/rc.d/init.d/README The etc directory is located under / -> here / is the parent and etc is the child. rc.d(child) is located under etc(parent) . init.d(child) is located under rc.d(parent) . README(leaf) is located under init.d(parent) . ==SUB-DIRECTORY:== A directory that has a parent directory. Note The root directory has no parent, and the lowest level subdirectory has no child. ...

Listing files and directories

One of the most rudimentary command in linux is ls. Some options of ls: Options Description -a Shows hidden files and directories. A file or directory name that begins with the period character. -l Displays long listing with detailed file information like file type, permissions, link count, owner etc. -ld Displays long listing of the specified directory but hides its contents. -lh Displays long listing with file sizes shown in human-friendly format. -lt Lists all files sorted by date and time with the newest file first. -ltr Lists all files sorted by date and time with the oldest file first (reverse). -R Lists contents of the specified directory and all its subdirectories (recursive listing). ls -l: Long listing of the files. ls -al: List all the hidden files in the current working directory. Debriefing the columns: Columns 1: The first character (hyphen or d) divulges the file type, and the next nine characters (rw-rw-r–) indicate permissions. Column 2: Displays the number of link. Column 3: Shows the owner name. Column 4: Exhibits the owning group name. Column 5: Identifies the file size in bytes. For directories, this number reflects the number of blocks being used by the directory to hold information about its contents. Column 6,7,8: Displays the month, day, and time of creation or last modification. Column 9: Indicates the name of the file or directory. ls -ll: Alternative of ls -l , does the same thing. ls -ld {directory_name}: Shows long listing of the specified directory. For example: ls -ld /usr ls -alh: To show all the files in the current directory with their sizes in human readable format. ls -lt: Shows the output in a sorted order by date and time with the newest file first. ls -R directory_name/by default the cwd is selected: Shows content of any specified directory recursively, if directory is not specified it will take the current working directory as a default argument. ...

Directory Basics

pwd(Present working Directory): It shows the a user’s current working directory. pwd always returns the absolute path. Navigating directories: Absolute path: It is the full path starting from the top level path which is / to my current working directory. The absolute path will always start with / at the beginning. Relative path: It is not a full path but rather a path which depicts the location relative to our own current working directory. For example: we are in /home/user1 directory. To move upwards either we can write using the relative path like this → cd Desktop/ , or we can write using absolute path like this → cd /home/user1/Desktop/ ...

Identifying terminal devices

Linux allocates unique pseudo (or virtual) numbered device files to represent terminal sessions opened by users on the system. It uses these files to communicate with individual sessions. By default, these files are stored in the /dev/pts (pseudo terminal session) directory. These files are created by the system when a user opens a new terminal session and they are removed on its closure. We can see it via the command tty(teletype)

System uptime

The uptime command is used to display the system’s current time, length of time it has been up for, number of users currently logged in, and the average CPU (processing) load over the past 1, 5, and 15 minutes. The output shows the current system time (18:28:09), up duration (49 minutes), number of logged-in users (2), and the CPU load averages over the past 1, 5, and 15 minutes (0.00, 0.00, and 0.00), respectively. The load average numbers correspond to the percentage of CPU load with 0.00 and 1.00 represent no load and full load, and a number greater than 1.00 signifies excess load (over 100%).

You know this alrady ;)

You can clear the terminal screen using the command clear .

Determining path of commands

RHEL provides a set of tools that can be used to identify the absolute path of the command that will be executed when you run it without specifying its full path. These tools are the which, whereis, and type commands. which: whereis: type:

Viewing system information

The uname command identifies elementary information about the system including its hostname. uname → shows only the kernel name. uname -a → showing all information Kernel name(1), hostname(2), kernel release(3), date and time of the kernel built(4), machine and hardware name(5), processor type(6), hardware platform(7), operating system name(8). More separate commands to try on uname

Viewing CPU information

We can see all cpu info using the command lscpu

How to get help when you are stuck in any command?

man pages: Press h to get help on navigation, press q to quit and return to the command prompt, use the Up and Down arrow keys to scroll up and down, and the PgUp and PgDn keys to scroll one page at a time. KEYS WHICH CAN HELP IN NAVIGATION: apropos command: It is alias of the command man -k {half_remembered_cmd_name} → This command allows us to perform keyword search on manual pages incase we have forgot what the command name is. Note Before we run the keyword search we need to run the command mandb ...