What is chmod in Linux?

chmod (change mode) is a Unix/Linux command used to control file system access permissions for file owners, group members, and all other users.

What does chmod 755 mean?

chmod 755 grants the Owner full read, write, and execute permissions (7), while Group and Others are granted read and execute permissions only (5). It is standard for directories and scripts.

What does chmod 644 mean?

chmod 644 gives the Owner read and write permissions (6), while Group and Others can only read the file (4). It is standard for web server HTML, CSS, and image files.

What are the numeric values for Read, Write, and Execute?

Read (r) equals 4, Write (w) equals 2, and Execute (x) equals 1. Adding these values together gives the octal digit (e.g., 4+2+1 = 7).

What permission should I use for SSH private keys?

SSH private keys (like ~/.ssh/id_rsa) should always use chmod 600 or 400 so only the file owner can read or modify the secret key.

Chmod Permissions Calculator

Calculate and convert Linux/Unix file permissions (octal, symbolic, chmod command).

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Common Presets:

Octal Notation

Symbolic Notation

-rwxr-xr-x

Equivalent Umask

0022

Target File or Directory Name

Terminal Chmod Command

chmod 755 script.sh

Recursive Command (Folders & Subfolders)

chmod -R 755 script.sh

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About Chmod Permissions Calculator

Chmod Permissions Calculator on TheToolss provides an interactive matrix to configure Linux and Unix file and folder permissions. Toggle Read (4), Write (2), and Execute (1) rights for Owner, Group, and Public/Others. Instantly get the corresponding Octal notation (e.g. 755, 644, 700), Symbolic notation (rwxr-xr-x), umask values, and generated chmod terminal commands with common security presets.

How to use Chmod Permissions Calculator

Select Read, Write, and Execute checkboxes for Owner, Group, and Others, or choose a preset.
Optionally customize your target file or directory name.
Copy the calculated octal value (e.g., 755), symbolic string, or ready-to-run terminal command.

Key features

Interactive permission matrix for Owner, Group, and Public users
Instant conversion between Octal (755), Symbolic (rwxr-xr-x), and Umask (022)
Pre-configured security presets for Web Files (644), Folders (755), and Private Keys (600)
Generates standard and recursive (chmod -R) shell commands
100% free, responsive, and private client-side calculator

Frequently asked questions

What is chmod in Linux?: chmod (change mode) is a Unix/Linux command used to control file system access permissions for file owners, group members, and all other users.
What does chmod 755 mean?: chmod 755 grants the Owner full read, write, and execute permissions (7), while Group and Others are granted read and execute permissions only (5). It is standard for directories and scripts.
What does chmod 644 mean?: chmod 644 gives the Owner read and write permissions (6), while Group and Others can only read the file (4). It is standard for web server HTML, CSS, and image files.
What are the numeric values for Read, Write, and Execute?: Read (r) equals 4, Write (w) equals 2, and Execute (x) equals 1. Adding these values together gives the octal digit (e.g., 4+2+1 = 7).
What permission should I use for SSH private keys?: SSH private keys (like ~/.ssh/id_rsa) should always use chmod 600 or 400 so only the file owner can read or modify the secret key.

Related In-Depth Guides

Learn practical workflows, real-world examples, and expert tips in our comprehensive guides:

Security & DevOps · 5 min read

User Role	Read (4)	Write (2)	Execute (1)	Summary
Owner (u)				Read, Write, Execute
Group (g)				Read, Execute
Others / Public (o)				Read, Execute