π Chmod Calculator
Click the permission bits or pick a preset to get the octal number, symbolic form, and shell command.
Permissions
How to Use This Chmod Calculator
Tick the nine permission boxes for user, group, and other, and the tool shows the octal number, the symbolic form, and the exact shell command. Or start from a preset.
Tick the Read, Write, and Execute boxes for the User (owner), Group, and Other columns. Each column also shows its bit values 4, 2, and 1.
Or click a preset button: 755 for scripts, 644 for regular files, 600 for private files, 777 to open everything, 400 for read-only.
Read the octal number (like 755), the symbolic form (like rwxr-xr-x), and the ready-to-run shell command.
Copy the command and run it on your server, replacing "filename" with your file or directory path.
How Octal Permissions Work
Every Linux file has nine permission bits: read, write, and execute for the user (owner), the group, and everyone else. Each bit has a numeric value: read is 4, write is 2, execute is 1. Add the values inside each class and you get one octal digit, so the nine bits become three digits like 755. User 7 means 4+2+1: read, write, execute. Group 5 means 4+1: read and execute, no write. Other 5 is the same. The symbolic form rwxr-xr-x says the same thing in letters: rwx for user, r-x for group, r-x for other. Once you see that each digit is just a sum of 4, 2, and 1, reading permissions becomes a habit instead of a lookup.
Worked Example
A deploy script needs to run, so the owner needs full control and everyone else only needs to run it: tick User Read+Write+Execute (4+2+1 = 7), Group Read+Execute (4+1 = 5), Other Read+Execute (4+1 = 5). The octal is 755, the symbolic form is rwxr-xr-x, and the command is chmod 755 deploy.sh. If the file were a private SSH key instead, you would tick only User Read+Write: 6, 0, 0, giving octal 600 and symbolic rw-------, and the command chmod 600 id_rsa.
Common Presets
Frequently Asked Questions
What does chmod 755 mean?
755 is octal for rwxr-xr-x. The owner can read, write, and execute (7 = 4+2+1), while the group and everyone else can read and execute but not write (5 = 4+1). It is the standard permission for executable scripts and web directories.
How do I read an octal permission like 644?
Read it digit by digit: user, group, other. Each digit is a sum of read (4), write (2), and execute (1). So 644 means user 6 (4+2: read and write), group 4 (read), other 4 (read), which is rw-r--r--. That is the standard permission for regular files.
What is the difference between 644 and 755?
Both let the owner read and write. The difference is the execute bit: 755 (rwxr-xr-x) grants execute to everyone, while 644 (rw-r--r--) grants no execute at all. Use 755 for scripts and directories, 644 for files that are only read, like HTML pages and images.
Is chmod 777 ever safe?
777 (rwxrwxrwx) lets every user on the system read, write, and execute the file. On a shared server or production machine that is a real security risk, since any compromised account can modify the file. Fix the underlying ownership or group problem instead; 777 is almost never the right answer.
Why do directories need the execute bit?
For directories, the execute bit means permission to enter and list contents. A directory with r-- but no x cannot be entered, which surprises people coming from Windows. That is why web directories are usually 755 rather than 744.