What does chmod 777 mean?

Chmod 777 grants full read, write, and execute permissions to everyone - the owner, the group, and all other users. In symbolic notation, this is rwxrwxrwx. While convenient, chmod 777 is a security risk and should be avoided for sensitive files. It's sometimes used temporarily for troubleshooting permission issues.

What is the difference between chmod 755 and chmod 644?

Chmod 755 (rwxr-xr-x) is typically used for directories and executable files - the owner has full permissions while group and others can read and execute. Chmod 644 (rw-r--r--) is the standard for regular files - the owner can read and write, while group and others can only read. These are the most common permission sets in Linux systems.

How do I convert octal permissions to symbolic notation?

Each octal digit (0-7) represents a combination of read (4), write (2), and execute (1) permissions. For example: 7 = rwx (4+2+1), 6 = rw- (4+2), 5 = r-x (4+1), 4 = r-- (4 only), 0 = --- (none). So chmod 755 becomes rwxr-xr-x: owner gets 7 (rwx), group gets 5 (r-x), others get 5 (r-x). Our calculator does this conversion automatically.

What are the default file permissions in Linux?

Default file permissions are typically 644 (rw-r--r--) for regular files and 755 (rwxr-xr-x) for directories. These defaults are controlled by the umask value, usually set to 022. The umask subtracts from the maximum permissions (666 for files, 777 for directories) to determine the actual default permissions.

Why can't I execute a script even with read permission?

To run a script directly (like ./script.sh), you need execute permission (x), not just read permission. Use chmod +x script.sh or chmod 755 script.sh to add execute permission. Alternatively, you can run the script through an interpreter (like bash script.sh) which only requires read permission.

What is the difference between chmod symbolic and numeric mode?

Numeric (octal) mode uses three digits (like 755) where each digit represents owner, group, and others permissions. Symbolic mode uses letters and operators (like u+x, g-w, o=r) to add, remove, or set specific permissions. Numeric mode sets absolute permissions, while symbolic mode can make relative changes. Both achieve the same result.

How do special permissions (setuid, setgid, sticky bit) work?

Special permissions add a fourth digit to chmod. Setuid (4) on executables runs them as the file owner. Setgid (2) on directories makes new files inherit the group. Sticky bit (1) on directories prevents users from deleting others' files (used on /tmp). For example, chmod 1755 sets sticky bit with standard directory permissions.

chmod

Chmod Calculator - Unix/Linux File Permission Calculator

Visual chmod permission calculator for Linux and Unix systems. Click to toggle read, write, and execute permissions for owner, group, and others. Convert between octal notation (777, 755, 644) and symbolic notation (rwxr-xr-x) instantly. Includes common presets for files and directories.

Numeric (Octal)

644

Symbolic

rw-r--r--

Command

chmod 644 filename

Enter octal mode

Read (4)Write (2)Execute (1)

Sum

Owner

Group

Others

Common Permission Sets

How it works

Each digit (0-7) represents permissions for owner, group, and others. 4 = read, 2 = write, 1 = execute. Add them up for each entity.

How to Use This Tool

Toggle Permissions

Click the checkboxes to set read (r), write (w), and execute (x) permissions for owner, group, and others

Or Enter Octal Mode

Type the octal number directly (e.g., 755, 644, 777) to see the permissions update automatically

Copy the Command

Copy the generated chmod command in octal or symbolic format to use in your terminal

Features

Visual Permission Builder

Interactive checkboxes for each permission
Separate controls for owner, group, others
Real-time updates as you click
Clear visual representation of permissions

Multiple Notations

Octal notation (755, 644, 777)
Symbolic notation (rwxr-xr-x)
Instant conversion between formats
Ready-to-use chmod commands

Common Presets

Standard file permissions (644)
Executable scripts (755)
Private files (600, 700)
Directory permissions

Understanding Unix File Permissions

Unix/Linux file permissions control who can read, write, and execute files and directories. Each file has three permission sets: one for the owner, one for the group, and one for all other users. These permissions are essential for system security and proper file access control.

The octal notation uses numbers 0-7, where each digit is the sum of: read (4), write (2), and execute (1). For example, 7 means all permissions (4+2+1), 5 means read and execute (4+1), and 0 means no permissions.

For directories, execute permission means the ability to enter (cd into) the directory, while read permission allows listing contents and write permission allows creating or deleting files within it.

Always use the principle of least privilege - grant only the minimum permissions necessary. Avoid using chmod 777 on production systems as it allows anyone to read, modify, and execute files, which is a significant security risk.

Frequently Asked Questions

Chmod (change mode) is a Unix/Linux command that changes file and directory permissions. Our chmod calculator provides a visual interface to set read (r), write (w), and execute (x) permissions for owner, group, and others. It instantly converts between octal notation (like 755) and symbolic notation (like rwxr-xr-x), generating the exact chmod command you need.

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