$ chmod
chmod Calculator
Convert between Unix file permission checkboxes, octal notation (755) and symbolic notation (rwxr-xr-x).
| Read (4) | Write (2) | Execute (1) |
Common:
Ad slot
Reading permissions
Three groups — owner, group, others — each with read (4), write (2) and execute (1). Add the numbers per group to get the octal digit: rwxr-xr-x is 7,5,5 → 755. On directories, execute means "can enter". setuid/setgid run a program as the file owner/group; sticky on a directory means only a file owner can delete their files (used on /tmp). These add a leading digit: chmod 1777 /tmp.