Convert between octal chmod values and rwx notation, including the setuid, setgid and sticky bits.
Tick the read, write and execute boxes for owner, group and other, and the octal value updates — or type the octal and watch the boxes follow.
The special bits are included: setuid runs a file as its owner, setgid as its group, and the sticky bit on a directory stops users deleting each other's files, which is what makes `/tmp` safe.
What is the difference between 755 and 644? 755 is the usual choice for directories and executables: the owner can write, everyone can read and traverse. 644 is for regular files: the owner can write, everyone can read, nobody executes.