chmod (change permissions) in Linux CLI - Time & Space Complexity

Time Complexity: chmod (change permissions)

O(n)

Understanding Time Complexity

When using chmod to change file permissions, it's helpful to understand how the time it takes grows as you change more files.

We want to know: how does the work increase when we apply chmod to many files?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

for file in /path/to/files/*; do
  chmod 644 "$file"
done
    

This script changes the permissions of every file in a folder to 644.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Running chmod on each file.
• How many times: Once for every file in the folder.

How Execution Grows With Input

As the number of files grows, the total work grows too because chmod runs once per file.

Input Size (n)	Approx. Operations
10 files	10 chmod commands
100 files	100 chmod commands
1000 files	1000 chmod commands

Pattern observation: The work grows directly with the number of files. Double the files, double the commands.

Final Time Complexity

Time Complexity: O(n)

This means the time to finish grows in a straight line with the number of files you change.

Common Mistake

[X] Wrong: "Running chmod on many files takes the same time as on one file."

[OK] Correct: Each file needs its own chmod command, so more files mean more work and more time.

Interview Connect

Understanding how commands like chmod scale helps you write scripts that run efficiently when handling many files.

Self-Check

"What if we used chmod with the -R option to change permissions recursively? How would the time complexity change?"