What does chmod 755 mean?

chmod 755 sets permissions to rwxr-xr-x. Owner has full read/write/execute permissions. Group and others can read and execute but cannot modify the file. This is the standard permission for executables and directories.

What is the difference between 644 and 755?

644 (rw-r--r--) is for files that should be readable by everyone but only editable by the owner - typical for web files. 755 (rwxr-xr-x) adds execute permission, needed for scripts and directories that people need to enter.

What is Setuid (SUID)?

Setuid (Set User ID) is a special permission that allows a file to be executed with the privileges of the file owner, not the user running it. Used for programs like passwd that need root access to modify system files. Represented as 4 in the special permission digit.

What is Setgid (SGID)?

Setgid (Set Group ID) works like SUID but for groups. On executables, it runs with the file's group permissions. On directories, new files inherit the directory's group instead of the user's primary group. Represented as 2 in the special permission digit.

What is the Sticky Bit?

The sticky bit (1) on directories restricts file deletion. Even if users have write permission to a directory, they can only delete files they own. Essential for shared directories like /tmp. Represented as 1 in the special permission digit.

Why should I avoid chmod 777?

777 gives everyone full read, write, and execute permissions. This is a security risk as any user or process can modify your files. Use the most restrictive permissions that still allow necessary access - usually 644 for files and 755 for directories.

chmod Calculator Pro - Advanced File Permissions | OpenKit

Quick Start Guide

1
Select permissions
Check the boxes for read, write, and execute permissions for owner, group, and others.
2
Add special permissions
Optionally enable Setuid, Setgid, or Sticky bit for advanced use cases.
3
Copy the command
Copy the generated chmod command in numeric or symbolic notation.

chmod (change mode) is a Unix/Linux command used to change the permissions of files and directories.

Every file in Linux has three permission types:

Read (r) - View file contents or list directory
Write (w) - Modify file or add/remove directory contents
Execute (x) - Run as a program or enter directory

Permissions are set for three user categories:

Owner (u) - The file's owner
Group (g) - Users in the file's group
Others (o) - Everyone else

This calculator helps you visualize and generate the correct chmod command with support for special permissions.

Web Server Files

Set 644 for HTML/CSS/JS files (owner can edit, others can read)

Executable Scripts

Set 755 for shell scripts and binaries that need to run

Private Config Files

Set 600 for SSH keys and sensitive configuration files

Shared Directories

Set 775 for team directories with shared write access

Setuid Binaries

Set 4755 for executables that need root privileges

Sticky Bit Folders

Set 1777 for /tmp directories where everyone can write but only owners can delete

The calculator provides two ways to specify permissions:

Numeric Notation (Octal) Each permission has a numeric value:

Read = 4
Write = 2
Execute = 1

Add values for each category:

7 (4+2+1) = rwx
6 (4+2) = rw-
5 (4+1) = r-x
4 (4) = r--

Symbolic Notation Use letters and operators:

u=user, g=group, o=others, a=all
- adds, - removes, = sets exactly
Example: chmod u+x,g-w file

Frequently Asked Questions

Follow the principle of least privilege:

Use 600 for sensitive files (SSH keys, passwords)
Use 644 for most web content
Use 755 for executables and directories
Never use 777 in production

Special permissions:

Only use SUID/SGID when absolutely necessary
Regularly audit files with special permissions: find / -perm /6000 -type f
Setuid scripts are dangerous - use compiled binaries instead

Regular maintenance:

Review file permissions periodically
Remove execute permission from files that don't need it
Ensure private keys are never world-readable

12+

Common Permissions

3 (rwx)

Permission Types

3 (SUID/SGID/Sticky)

Special Bits

Quick Start Guide

1
Select permissions
Check the boxes for read, write, and execute permissions for owner, group, and others.
2
Add special permissions
Optionally enable Setuid, Setgid, or Sticky bit for advanced use cases.
3
Copy the command
Copy the generated chmod command in numeric or symbolic notation.

chmod (change mode) is a Unix/Linux command used to change the permissions of files and directories.

Every file in Linux has three permission types:

Read (r) - View file contents or list directory
Write (w) - Modify file or add/remove directory contents
Execute (x) - Run as a program or enter directory

Permissions are set for three user categories:

Owner (u) - The file's owner
Group (g) - Users in the file's group
Others (o) - Everyone else

This calculator helps you visualize and generate the correct chmod command with support for special permissions.

Web Server Files

Set 644 for HTML/CSS/JS files (owner can edit, others can read)

Executable Scripts

Set 755 for shell scripts and binaries that need to run

Private Config Files

Set 600 for SSH keys and sensitive configuration files

Shared Directories

Set 775 for team directories with shared write access

Setuid Binaries

Set 4755 for executables that need root privileges

Sticky Bit Folders

Set 1777 for /tmp directories where everyone can write but only owners can delete

The calculator provides two ways to specify permissions:

Numeric Notation (Octal) Each permission has a numeric value:

Read = 4
Write = 2
Execute = 1

Add values for each category:

7 (4+2+1) = rwx
6 (4+2) = rw-
5 (4+1) = r-x
4 (4) = r--

Symbolic Notation Use letters and operators:

u=user, g=group, o=others, a=all
- adds, - removes, = sets exactly
Example: chmod u+x,g-w file

Frequently Asked Questions

Follow the principle of least privilege:

Use 600 for sensitive files (SSH keys, passwords)
Use 644 for most web content
Use 755 for executables and directories
Never use 777 in production

Special permissions:

Only use SUID/SGID when absolutely necessary
Regularly audit files with special permissions: find / -perm /6000 -type f
Setuid scripts are dangerous - use compiled binaries instead

Regular maintenance:

Review file permissions periodically
Remove execute permission from files that don't need it
Ensure private keys are never world-readable

12+

Common Permissions

3 (rwx)

Permission Types

3 (SUID/SGID/Sticky)

Special Bits

chmod Calculator Pro

Owner (u)

Group (g)

Others (o)

Special Permissions

Quick Start Guide

Quick Start Guide

Select permissions

Add special permissions

Copy the command

What is chmod?

Common Use Cases

Web Server Files

Executable Scripts

Private Config Files

Shared Directories

Setuid Binaries

Sticky Bit Folders

How to Use the chmod Calculator

Frequently Asked Questions

Frequently Asked Questions

What does chmod 755 mean?

What is the difference between 644 and 755?

What is Setuid (SUID)?

What is Setgid (SGID)?

What is the Sticky Bit?

Why should I avoid chmod 777?

Security Best Practices

By the Numbers

Related Tools

chmod Calculator Pro

Owner (u)

Group (g)

Others (o)

Special Permissions

Quick Start Guide

Quick Start Guide

Select permissions

Add special permissions

Copy the command

What is chmod?

Common Use Cases

Web Server Files

Executable Scripts

Private Config Files

Shared Directories

Setuid Binaries

Sticky Bit Folders

How to Use the chmod Calculator

Frequently Asked Questions

Frequently Asked Questions

What does chmod 755 mean?

What is the difference between 644 and 755?

What is Setuid (SUID)?

What is Setgid (SGID)?

What is the Sticky Bit?

Why should I avoid chmod 777?

Security Best Practices

By the Numbers

Related Tools