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Chmod Calculator

Calculate chmod permissions visually

Owner
7
Group
5
Others
5
Numeric
755
Symbolic
rwxr-xr-x
Command
chmod 755 filename
Common Presets

About Chmod Calculator

Unix file permissions are three sets of three bits — read, write, execute for owner, group, and others. The octal representation (755, 644, 700) maps directly to those bit patterns, but remembering the mapping while setting permissions under pressure is error-prone. Toggle the checkboxes and see the octal value and symbolic notation update in real time. Or type an octal value like 755 and see exactly what each bit means. The chmod command is generated automatically and ready to copy. Common values: 755 for executables and directories, 644 for files, 700 for private files, 777 (avoid in production).

Common Use Cases

  • →Figuring out the right chmod value for a shell script or binary
  • →Understanding what 755 or 644 actually means in terms of who can do what
  • →Generating the correct chmod command for a deployment script
  • →Debugging permission denied errors on a server

Frequently Asked Questions

How does octal map to permissions?+
Each octal digit represents 3 bits: 4=read, 2=write, 1=execute. Add them for combinations: 7=rwx, 6=rw-, 5=r-x, 4=r--. The three digits are owner, group, others. So 755 = owner rwx, group r-x, others r-x.
What is the difference between owner, group, and others?+
Owner is the user who owns the file. Group is any user in the file's assigned group. Others is everyone else. Unix checks them in order — if you are the owner, owner permissions apply regardless of group.
What is the execute bit on a directory?+
For directories, execute means "traverse" — the ability to cd into it and access its contents. Without execute on a directory, you cannot enter it even if you have read permission to list its contents.
When should I use 777?+
Almost never on a server. 777 gives write permission to every user on the system. The only legitimate use is for shared writable temporary directories in controlled environments. On production servers, it is a security risk.