100 Days of DevOps: Day 4

How to Grant Executable Permissions to a Script

Why Permissions Matter

In a Linux or Unix-like operating system, file permissions are a fundamental security feature. They control who can read, write, or execute a file. This is crucial for system stability and security, as it prevents unauthorized users from running scripts that could harm the system or access sensitive information.

When you create a new script (like a .sh file), it usually doesn't have executable permissions by default. This is a safety measure. Before you can run it, you must explicitly tell the system that the file is safe to execute.

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The chmod Command

The command used to change file permissions is chmod, which stands for "change mode." There are two main ways to use it: with symbolic notation and with octal (numeric) notation.

1. Symbolic Notation

This method is often the easiest to remember. You use a combination of letters to specify the permissions you want to change.

• u = user (owner)

• g = group

• o = others

• a = all (user, group, and others)

• + = add a permission

• - = remove a permission

• = = set a permission

• r = read

• w = write

• x = execute

To grant all users executable permissions for the /tmp/wycliffe.sh script, you would use:

chmod a+x /tmp/wycliffe.sh

This command literally means "change mode for all users, add the execute permission."

2. Octal (Numeric) Notation

This method uses a three-digit number to set permissions for the user, group, and others. Each digit is a sum of the permissions:

• 4 = read (r)
• 2 = write (w)
• 1 = execute (x)

So, to grant read and execute permissions, you'd use 4 + 1 = 5. To grant all three, you'd use 4 + 2 + 1 = 7.

A common permission set for scripts is 755. This means:

• 7 (user): read, write, and execute permissions
• 5 (group): read and execute permissions
• 5 (others): read and execute permissions

To apply this to your script, you'd run:

chmod 755 /tmp/wycliffe.sh

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Verifying the Change

After you've run the command, you can confirm the change by using the ls -l command.

ls -l /tmp/wycliffe.sh

The output will show a string of permissions at the beginning. If the script is executable for all, it will look something like this:

-rwxr-xr-x 1 user group 1234 Aug 7 09:00 /tmp/wycliffe.sh

The x in the output confirms that the execute permission has been successfully granted.