What does “> /dev/null 2>&1″ mean?

A lot time we come across a command like
ls > /dev/null 2>&1

This command will produce no output at all, i.e. to STDOUT and no STDERR. The reason for this is that greater-thans (>) in commands like these redirect the program’s output somewhere. In this case, something is being redirected into /dev/null, and something is being redirected into &1.

There are three standard sources of input and output for a program. Standard input usually comes from the keyboard if it’s an interactive program, or from another program if it’s processing the other program’s output. The program usually prints to standard output, and sometimes prints to standard error. These three file descriptors (you can think of them as “data pipes”) are often called STDIN, STDOUT, and STDERR.

Sometimes they’re not named, they’re numbered. The built-in numberings for them are 0, 1, and 2, in that order. By default, if you don’t name or number one explicitly, you’re talking about STDOUT.

Given that context, the command above is redirecting standard output into /dev/null, which is a place you can dump anything you don’t want (often called the bit-bucket), then redirecting standard error into standard output (you have to put an & in front of the destination when you do this) and since standard output is going to /dev/null hence standard error will also go to /dev/null and hence this command will produce no output