Linux Commands That Look Simple but Are Essential for Everyday DevOps Tasks

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Usually when you start working with Linux and begin learning DevOps, you need to become familiar with Linux commands. To fully understand what you are doing, it is very important to have a strong foundation. This article will help you gain that stronger understanding of the fundamentals that you need to master the technical aspects of DevOps.

In this article, we are going to take a deep dive into some commonly used Linux commands that can have significant impact on strengthening your fundamentals knowledge. I will break down the content into following topics and will also explain practical scenarios that you can try yourself to get hands on experience.

1. Introduction and Usage

2. The “pwd” Command and Its Behavior

3. The “ls” Command and Its Behavior

4. The “cd” Command and Its Behavior

5. The “mkdir” Command and Its Behavior

6. The “cp” Command and Its Behavior

7. The “chmod” Command and Its Behavior

Introduction and Usage

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When you initially take dive into DevOps as a beginner or start using Linux components these commands would appear everywhere.

These commands would appear in docker tutorials, CI/CD pipelines, cloud servers, deployment scripts, Kubernetes containers and troubleshooting guides as a software engineer these are like must know facts.

As a DevOps Engineer or as a Software Engineer you may need to

1. Navigate through server directories
2. Inspect application files
3. Create deployment folders
4. Copy configuration files
5. Run shell scripts
6. Change file permissions
7. Investigate file permissions
8. Investigate application logs
9. Troubleshoot failed deployments

Basic Linux commands help us perform all these tasks.

The “pwd” Command and Its Behavior

pwd - Find your current location

The pwd command means basically print the working directory.

pwd --> execute command
/mnt/c/Users/User1/linux-practise  --> example output

This command is mostly helpful to identify whether you are in the correct application directory.

The “ls” Command and Its Behavior

ls - list

The ls command displays the files and directories inside your current location.

Say for an example your directory contains below files, then the ls command would print out all the files in the terminal.

1. index.js
2. readme.txt
3. services.js

Useful ls options

ls-l : Long format

ls-l

This displays

1. File permissions
2. File owner
3. Group
4. File size
5. Last modified date
6. File or directory name

When you run the command ls-l you will get an output like below. Through the below diagrams you can learn exactly what this result expresses.

-rwxrwxrwx 1 user1 user1 0 Jul 18 21:09 sample.txt 

ls-l command explanation

File permissions

Hope you now has a better understanding of what interprets from the longer format of ls command.

ls -a : Display hidden files

This command usually brings out the files which are hidden.

Display hidden files with Details : ls — la

The ls command variations discussed above are widely used in day-to-day DevOps work and Linux environments. I hope you now have a better understanding of how they work.

The “cd” Command and Its Behavior

The cd command means change directory.

This command allow us to move from directory to another.

You can use to enter a directory : cd frontend To move back one level : cd .. To returns home directory: cd ~ To move to root directory: cd / To return to previous directory : cd -

You can also you relative path and absolute path with the cd command as well.

Relative path starts from your current location. cd project/src/components

Absolute path start from your Linux root directory cd /home/username/project/src/components

Common Linux Path Symbols

The “mkdir” Command and Its Behavior

The mkdir command means make directory.

It creates a new folder

mkdir deployment

you can create several directories at once: mkdir dev test production

Creating Nested directories

use -p option to create parent and child directories together.

mkdir -p application/config/nginx

This command create the complete directory structure.

Folder structure created by the mkdir -p command

Without -p, the command may fail if the parent directories do not already exist

mkdir: cannot create directory ‘application/config/nginx’: No such file or directory

The “cp” Command and Its Behavior

The cp command means copy.

Its basic structure is cp SOURCE DESTINATION

Copy a File

cp config.json config-backup.json This creates a copy of **config.json named `config-backup.json`**

Copy a file into another directory

cp config.json backup/

Copy and rename a file

cp config.json backup/old-config.json

Copy a directory

To copy a directory and everything inside it, use the **-r **option:

cp -r frontend frontend-backup

The **-r means recursive**.

Without **-r**, Linux will not normally copy a directory.

The “chmod” Command and Its Behavior

The **chmod command stands for change mode. It is used to change the permissions of files and directories in Linux**.

Permissions determine who can read, modify or execute a file.

Basic Syntax is: chmod PERMISSONS FILE_NAME

Example : chmod 755 deploy.sh This changes the permissions of the deploy.sh file

The three main permissions are

Permission types

Linux permissions are normally assigned to three categories

Permission groups

The permission order is always

Read → Write → Execute

The category order is always

User/Owner → Group → Others

For example:

rwx

means that read, write, and execute permissions are granted.

r-x

means:

r = Read permission is granted
- = Write permission is not granted
x = Execute permission is granted

The dash does not represent another permission. It shows that the permission in that position is missing.

Permission set Meaning

rwx   Read, write, and execute
rw-   Read and write
r-x   Read and execute
r--   Read only
-w-   Write only
--x   Execute only
---   No permissions

In an ls -l result such as: -rwxr-xr-x

the permissions are divided like this

Permission flow

Numeric Permission Method

Linux permissions can be represented using numbers.

Numeric permission

Number Permission result

7 : Read, write, and execute
6 : Read and write
5 : Read and execute
4 : Read only
3 : Write and execute
2 : Write only
1 : Execute only
0 : No permissions

Understanding chmod 755

Consider this command:

chmod 755 deploy.sh

The three digits follow this order:

755 command explanation

The meaning is:

User/owner: 7 = read + write + execute
Group:      5 = read + execute
Others:     5 = read + execute

In permission symbols, this becomes:

rwxr-xr-x

After running the command, ls -l may display:

-rwxr-xr-x 1 user1 user1 120 Jul 18 21:09 deploy.sh

The owner can read, modify, and execute the script. The group and other users can read and execute it, but they cannot modify it.

Symbolic Permission Method

Linux also allows permissions to be changed using letters.

The general format is:

who + action + permission

For example:

u + x

means:

u = User/owner
+ = Add permission
x = Execute permission

Therefore:

chmod u+x deploy.sh

means:

Add execute permission for the file owner.

Permission Operators

Symbolic mode uses three main operators:

Permission Operators

Add a permission

chmod u+x deploy.sh

Adds execute permission for the owner.

Suppose the owner previously had: rw- After adding execute permission, it becomes: rwx

Remove a permission

chmod g-w deploy.sh

Removes write permission from the group.

Set exact permissions

chmod u=rx deploy.sh

Sets the owner permissions to read and execute only.

If the owner previously had write permission, it will be removed because = replaces the existing permission set.

Below are few examples I came up with so you could have a better understanding.

Add read permission for the group:

chmod g+r file.txt

Remove write permission from others:

chmod o-w file.txt

Add execute permission for everyone:

chmod a+x deploy.sh

Here, a means all categories: a = user + group + others

Set different permissions for all three categories:

chmod u=rwx,g=rx,o=rx deploy.sh

u=rwx User/owner receives read, write, and execute 
g=rx  Group receives read and execute 
o=rx  Others receive read and execute

This command is equivalent to:

chmod 755 deploy.sh

However, the following command is not valid:

chmod rwxr-xr-x deploy.sh

When using symbolic mode, the categories such as **u, `g, **ando` must be included.

The correct symbolic form is:

chmod u=rwx,g=rx,o=rx deploy.sh

Numeric Mode vs Symbolic Mode

Both change the permissions but they are used in different scenarios.

Numeric mode

chmod 755 deploy.sh

Numeric mode sets the complete permission structure. It is useful when you already know the exact permissions required.

Symbolic mode

chmod u+x deploy.sh

Symbolic mode changes only a specific permission. It is useful when you want to add or remove one permission without changing the others.

For example:

chmod u+x deploy.sh

only adds execute permission for the owner.

However:

chmod 755 deploy.sh

replaces the complete owner, group, and others permission structure.

I hope you now have a better understanding of these Linux commands and have strengthened your fundamental knowledge. The best way to become confident with Linux is to practise these commands and try them yourself in different scenarios. You can also return to this article whenever you need to refresh your knowledge and reinforce what you have learned.