755 gives the owner read, write, and execute permissions (7), while the group and others receive read and execute permissions (5). Its symbolic form is rwxr-xr-x. It is a common combination for executable files and directories that other users may access but not modify.

644 is rw-r--r--: the owner can read and write, while everyone else can only read. 755 is rwxr-xr-x and adds execute permission for all three subjects. Regular data files often do not need execute permission; directories need execute permission to be traversed. Choose based on what the file or directory must actually allow.

setuid is used on selected executables that must run with the file owner's effective identity. setgid can do the equivalent for a file's group and is also useful on collaborative directories so new entries inherit the directory group. The sticky bit is commonly used on shared writable directories so users cannot remove entries owned by others. Each changes security behavior and should be enabled deliberately.

Those letters occupy an execute position. Lowercase s or t means both the special bit and execute permission are enabled at that position. Uppercase S or T means the special bit is enabled but execute permission is absent. This distinction prevents a special bit from hiding whether the underlying execute bit is set.

No. It only converts the permission value you enter and prepares command text inside your browser. It cannot inspect your filesystem or execute terminal commands, and your input is not uploaded. Review the generated permission and add the correct path before running the command yourself.