Question

In Linux, what is the difference between /dev/ttyS0 and /dev/ttys0?

I know that the first is a serial port, but what about the second, with the small s?

Answer 1

see this

For a pseudo terminal pair such as ptyp3 and ttyp3, the pty… is the master or controlling terminal and the tty… is the slave. There are only 16 ttyp’s: ttyp0-ttypf (f is a hexadecimal digit). To get more pairs, the 3 letters q, r, s may be used instead of p. For example the pair ttys8, ptys8 is a pseudo terminal pair. The master and slave are really the same ‘port’ but the slave is used by the application program and the master is used by a network program (or the like) which supplies (and gets) data to/from the slave port.