On
UNIX system,
programs and
commands send error messages to
users
by writing to standard error, which is by convention assigned in the process as
file descriptor 2. This allows a clean
separation between normal
output and
error output.
Though standard error is usually the terminal, the user can redirect standard error to /dev/null or some other device or file, in most shells using '2>'. i.e:
command 2> /dev/null
See also about
standard input and
standard output.