Calculate Linux/Unix file permissions visually. Select read, write, and execute permissions for owner, group, and others to instantly generate the chmod numeric value (e.g. 755, 644) and the corresponding shell command.
chmod (change mode) is a Unix/Linux command that modifies file and directory permissions.
755 means owner has read+write+execute (7), group and others have read+execute (5). Commonly used for web server directories.
Numeric chmod (e.g. 755) adds read (4), write (2), and execute (1) together for each of owner, group, and others. Symbolic chmod (e.g. chmod u+x) is more readable and lets you add or remove specific permissions without affecting others. Both are equivalent; numeric notation is more common in scripts and documentation.
Follow the principle of least privilege — grant only necessary permissions. Avoid chmod 777 (read/write/execute for everyone), which is a serious security risk. For web servers, use 644 for files and 755 for directories. Confirm current permissions with ls -la before changing. Be especially careful with system files; incorrect permissions can prevent services from starting or create security vulnerabilities.