Basic Linux Commands and File Management in CentOS 7

Aim

To study basic Linux commands for identifying users, creating and editing files, switching users, checking paths, file ownership, permissions, and searching text using grep.

Requirements

CentOS 7 environment
Terminal access with root and non-root (bit) users
vim editor

Identification of Root and Non-Root Users

The terminal prompt indicates the type of user currently logged in:

Root user: [root@lab1-m13 ~]#
- # indicates that the current user is root.
Non-root user: [bit@lab1-m13 ~]$
- $ indicates that the current user is a non-root user.

Check the Current Path

The pwd command displays the current working directory:

pwd

The home directory of the root user is /root. The home directory of a non-root user such as bit is /home/bit.

Switch Users

The su command switches from one user to another:

The su - form switches the user and starts a login shell with the target user’s environment and home directory:

su - bit
su -

The su command without - switches the effective user without starting a full login shell.

Create a File

The touch command creates an empty file:

touch test.txt

Check whether the file was created:

ls -l test.txt

Display File Contents

The cat command displays the contents of a file:

cat test.txt
cat /root/test.txt

Create and Edit a File Using Vim

The vim editor can be used to create and edit a file:

vim test.txt

Enter insert mode and write the content, for example: This file is created by Debojit.
Press Esc to leave insert mode.
Press Shift + : to open the command line.
Type wq and press Enter.

wq means write and quit: save the file and exit Vim.

Check File Ownership and Permissions

The ls -l command displays the ownership and permissions of a file:

ls -l test.txt

Example output:

-rw-r--r-- 1 root root 0 Aug 10 11:01 test.txt

In this output:

The first root is the file owner.
The second root is the group owner.

File Permissions

A typical permission entry is:

-rw-r--r--

The first character represents the file type:
- - — regular file
- d — directory
The remaining nine characters represent permissions for:
- User
- Group
- Others

Permission values are:

Permission	Meaning	Value
`r`	Read	4
`w`	Write	2
`x`	Execute	1

Therefore, rwx = 4 + 2 + 1 = 7.

Full permission for a directory is 777:

7 | 7 | 7
User | Group | Others

Each category has read, write, and execute permission. For a file, full permission is 666.

Check Directory Details

To display the details of the /root directory itself, use:

ls -ld /root

ls — list
-l — long format
-d — display the directory itself
/root — target directory

Use of the `grep` Command

The grep command searches for a particular word or pattern in text or command output:

ls -l / | grep root

Here:

ls -l / lists the contents of the root directory /.
The pipe symbol (|) passes the output of the first command to grep.
grep root displays only the lines containing the word root.

Therefore, ls -l / | grep root lists the contents of / and displays only the lines containing root.

Result

The basic Linux commands for user identification, user switching, file creation, file editing, path checking, file ownership, permissions, and text searching were studied and executed successfully.