The signals listed in this section are used in conjunction with
asynchronous I/O facilities. You have to take explicit action by
fcntl to enable a particular file descriptor to generate
these signals (see Interrupt Input). The default action for these
signals is to ignore them.
On most operating systems, terminals and sockets are the only kinds of files that can generate
SIGIO; other kinds, including ordinary files, never generate
SIGIOeven if you ask them to.
In the GNU system
SIGIOwill always be generated properly if you successfully set asynchronous mode with
This signal is sent when “urgent” or out-of-band data arrives on a socket. See Out-of-Band Data.