Chmod Calculator

Calculate Unix/Linux file permissions. Toggle read, write, execute for owner, group, and others.

Free to use. Runs in your browser.

Set file permissions by toggling checkboxes or entering an octal number like 755.

Use it to turn read, write, and execute choices into the exact chmod command you need.

Enter Octal (e.g. 755)

Owner (User)

ReadWriteExecute

Group

ReadWriteExecute

Others (World)

ReadWriteExecute

Octal

755

Symbolic

-rwxr-xr-x

Command

chmod 755 filename

Unix File Permissions: How They Work

Every file and directory on a Unix/Linux system has three sets of permissions: one for the owner, one for the group, and one for everyone else. Each set controls three actions: read (r), write (w), and execute (x). That's 9 permission bits total, which is why chmod uses 3-digit octal numbers, each digit encodes one set.

The number system is elegant: read = 4, write = 2, execute = 1. Add them up for each group. So 7 (4+2+1) means full access, 5 (4+1) means read and execute, 6 (4+2) means read and write. chmod 755 gives the owner full access and everyone else read/execute, the most common permission for web directories and scripts.

Getting permissions wrong causes two kinds of problems: too restrictive (users can't access what they need) or too permissive (security vulnerability). This calculator helps you find the exact permission set for your use case.

Common Permission Patterns

Octal	Symbolic	Use Case
644	-rw-r--r--	Standard files (HTML, CSS, images, configs)
755	-rwxr-xr-x	Directories, executable scripts, web root folders
600	-rw-------	SSH keys, .env files, private credentials
700	-rwx------	Private scripts, .ssh directory
775	-rwxrwxr-x	Shared group directories, deployment folders
444	-r--r--r--	Read-only files, system configs you don't want modified
777	-rwxrwxrwx	AVOID, full access for everyone (security risk)

What this means for you: 99% of the time you need either 644 (files) or 755 (directories/scripts). If you're reaching for 777, stop, there's almost always a better solution involving group permissions or ACLs.

Permission Mistakes That Cause Real Problems

SSH key too permissive

SSH refuses to use keys with permissions other than 600 or 400. "Permissions 0644 for 'id_rsa' are too open" is one of the most common SSH errors. Fix: chmod 600 ~/.ssh/id_rsa

Web server 403 errors

Nginx/Apache return 403 Forbidden when they can't read files. Usually the web server user needs read access (644 for files, 755 for directories). Check both the file AND every parent directory in the path.

Script won't execute

"Permission denied" when running a script usually means it lacks the execute bit. Fix: chmod +x script.sh (adds execute for everyone) or chmod 755 script.sh (explicit full permission set).

chmod 777 on production

Giving everyone write access to web files means any compromised process can modify your site. This is how many web defacement attacks succeed. Use proper group permissions instead of 777.

Permission Number Quick Reference

Number	Permission	Binary
0	No access	000
1	Execute only	001
2	Write only	010
3	Write + execute	011
4	Read only	100
5	Read + execute	101
6	Read + write	110
7	Read + write + execute	111

Each digit in a chmod number (e.g., 755) maps to one of these values. The first digit is the owner, second is the group, third is everyone else. So 755 = owner gets 7 (rwx), group gets 5 (r-x), others get 5 (r-x).

Worked Example: Fixing a Static Site Deploy

Aisha deploys a small React site to a Linux server. The browser shows a 403 error for the homepage, while SSH access still works. The web root is /var/www/site.

1. Check the directory path

The web server needs execute permission on every directory it traverses. For public static assets, 755 is usually right for directories.

2. Check ordinary files

HTML, CSS, JS, and images need read permission. They do not need execute permission, so 644 is the usual file value.

3. Avoid the 777 shortcut

777 would hide the symptom but give every local account write access. Fix the owner or group instead.

4. Apply targeted commands

One safe pattern is find /var/www/site -type d -exec chmod 755 {} \;and find /var/www/site -type f -exec chmod 644 {} \;.

Commands to Inspect Permissions

chmod changes permissions, but it is rarely the first command you should run. Inspect the current owner, group, and mode before changing anything, especially on shared servers.

Command	What it shows	Use it when
ls -l file	Symbolic mode, owner, group, and size	You need a quick read of one file
stat file	Numeric mode such as 0644 plus metadata	You need the exact octal value
namei -l path	Permissions for each directory in a path	A web server can read the file but not reach it
getfacl file	Access control lists beyond standard chmod bits	Permissions look correct but access still fails

Special Bits, Umask, and Sticky Directories

setuid, leading 4

On executables, setuid runs the program as the file owner. This is sensitive because a bug in the program may become a privilege escalation. Do not set it unless you know why.

setgid, leading 2

On directories, setgid makes new files inherit the directory group. It is useful for shared deploy folders where several users should write into the same group-owned tree.

sticky bit, leading 1

The sticky bit lets many users write to a directory while stopping them from deleting each other's files. /tmp commonly uses it.

umask defaults

umask decides the default permissions for new files and directories. If new files keep appearing as 600 or 664, check the shell, service, or deployment umask before changing every file after the fact.

Safer chmod Troubleshooting Checklist

Start with ownership. If the wrong user owns the file, chmod may only mask the real issue. Check ls -l before changing modes.
Separate files from directories. Directories need execute permission to be entered. Ordinary files do not need execute permission unless they are scripts or binaries.
Keep secrets tighter than web assets. Use 600 for private keys and sensitive config files. Do not copy public web-file defaults onto secrets.
Be careful with recursive changes. chmod -R changes every nested item. Use find -type f and find -type d when files and folders need different modes.
Check ACLs and mounts. Network drives, Docker volumes, and ACLs can override what chmod appears to say. If a mode looks right but access still fails, inspect the filesystem context.

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How to use this tool

Toggle read, write, execute checkboxes for owner, group, and others

Or enter a 3-digit octal number and click Apply

Copy the chmod command to use in your terminal

Common uses

Setting correct permissions for web server files
Fixing SSH key permission errors
Configuring deployment script permissions
Understanding and debugging Unix permission issues

Share this tool

Frequently Asked Questions

What is chmod?

chmod (change mode) is a Unix/Linux command that sets file or directory permissions for the owner, group, and others.

What do the numbers mean?

Each digit represents a permission set: 4 = read, 2 = write, 1 = execute. They're added together, e.g. 7 = read + write + execute.

What is a common chmod value?

755 is common for directories and scripts (owner: rwx, group/others: r-x). 644 is common for files (owner: rw-, group/others: r--).

What does chmod 777 mean?

chmod 777 grants read, write, and execute permissions to everyone. It's generally insecure and should be avoided in production.

What's the difference between chmod 644 and 755?

644 is for files: the owner can read and write; everyone else can only read. 755 is for files or directories: the owner can read, write, and execute; everyone else can read and execute. Use 644 for HTML, CSS, and config files; use 755 for scripts and directories.

How do I apply chmod recursively to a directory?

Use the -R flag: chmod -R 755 my-folder/. This applies the permission to the folder and every file and subfolder inside it. Be careful, recursive chmod can unintentionally make files executable or remove needed permissions on system folders.

What are special permission bits (setuid, setgid, sticky)?

The leading 4 (setuid), 2 (setgid), or 1 (sticky) digit adds special behaviour. Setuid makes an executable run with the owner's privileges, common on binaries like passwd. Setgid on directories makes new files inherit the directory's group. The sticky bit on shared directories like /tmp stops users deleting each other's files.

Should directories and files use the same chmod value?

Usually no. Directories need execute permission so users and services can enter them, while ordinary files only need execute permission when they are scripts or binaries. A common deploy pattern is 755 for directories and 644 for static files.

Why does SSH reject my private key?

SSH refuses to use a private key that other users can read. Use chmod 600 for a private key such as ~/.ssh/id_rsa, and use chmod 700 for the ~/.ssh directory so only your account can read or enter it.

What should I use instead of chmod 777?

Start by fixing ownership with chown or by adding the service account to the right group. If a web app needs write access to uploads, grant write access to that one directory instead of making the whole project writable by everyone.

Why can a directory need execute permission?

On directories, execute means traverse. A user or web server may need execute permission on a directory to reach files inside it, even if the files themselves already have read permission.

Results are for general informational purposes only and should be checked before use. They are not professional advice. See our Disclaimer and Terms of Service.