Chmod Calc

chmod (change mode) is a Unix command that sets file or directory permissions. It controls who can read, write, and execute files on Unix-like operating systems including Linux and macOS.

755 means the owner can read, write, and execute (7=4+2+1); the group can read and execute (5=4+1); and others can read and execute (5=4+1). This is the standard permission for executable files and directories.

644 means the owner can read and write (6=4+2); the group and others can only read (4). This is the standard permission for regular files.

Numeric notation uses three digits (e.g., 755) where each digit represents owner, group, and other permissions. Symbolic notation uses letters (e.g., rwxr-xr-x) where r=read, w=write, x=execute.

777 gives full read, write, and execute permissions to everyone on the system. This is a security risk because any user or process can modify or execute the file.