As we know ,
File descriptor 1 is the standard output (stdout).
File descriptor 2 is the standard error (stderr).
Here is one way to remember this construct (although it is not entirely accurate): at first, 2>1 may look like a good way to redirect stderr to stdout.
However, it will actually be interpreted as "redirect stderr to a file named 1". & indicates that what follows and precedes is a file descriptor and not a filename. So the construct becomes: 2>&1.
Consider >& as redirect merger operator.
–Credits: Ayman Hourieh , Smart Manoj