argument is non-zero,
will close the first three file descriptors and redirect them to
Normally, these correspond to standard input, standard output, and
However, if any of those file descriptors refer to something else, they
will still be closed, resulting in incorrect behavior of the calling program.
This can happen if any of standard input, standard output, or standard
error have been closed before the program was run.
should therefore either call
before opening any files or sockets, or verify that any file
descriptors obtained have values greater than 2.
function temporarily ignores
to prevent a parent session group leader's calls to
from prematurely terminating the child process.