Day-4 Script Execution Permissions

Introduction

In Linux, not all files are created equal — some are just data, while others are scripts or programs that you can run.
Before a script can be executed, it needs the right permissions.

In this guide, we’ll explore:

• How Linux handles execution permissions

• How to grant or revoke execution rights

• Best practices for secure script execution

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📂 Understanding Linux File Permissions

Every file in Linux has three sets of permissions:

• Owner (user)

• Group

• Others (everyone else)

Each set can have:

• r → Read

• w → Write

• x → Execute

You can see permissions with:

ls -l script.sh

Example:

-rwxr-xr--  1 ramya  devs  1024 Aug  9 15:12 script.sh

Here:

• rwx → Owner can read, write, execute

• r-x → Group can read and execute

• r-- → Others can read only

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🚀 Giving Execute Permissions to a Script

1️⃣ Using chmod

The chmod command changes file permissions.

Give execute permission to the owner:

chmod u+x script.sh

Give execute permission to everyone:

chmod +x script.sh

Remove execute permission from others:

chmod o-x script.sh

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2️⃣ Using Numeric Permissions

Linux also supports octal (numeric) permission notation.

Example:
Owner = 7 (read + write + execute), Group = 5 (read + execute), Others = 5 (read + execute):

chmod 755 script.sh

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🔍 Running a Script

Once executable, you can run it in two ways:

Directly (requires x permission):

./script.sh

Using an interpreter (does not require x permission):

bash script.sh
python3 script.py

Even without chmod +x, you can run a script if you call it through its interpreter.

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⚠️ Security Best Practices

• Avoid chmod 777 → This gives full permissions to everyone and is a security risk.

• Limit to necessary users → Use chmod 700 for private scripts.

• Use proper ownership → Ensure scripts belong to the correct user (chown command).

• Validate content → Never execute scripts from untrusted sources.