nullmodem - Man Page

a Utility to loopback Pseudo-Terminals


nullmodem [-F] [-V] [-q] [-r] [-m] tty...


nullmodem creates a virtual network of Pseudo-Terminals. It can be used as an adapter to connect two programs that normally need serial interface cards.


-F, --foreground

Unlike normal operation, nullmodem will not detach from the terminal when given this option. Some debugging informations will be visible.

-q, --quiet

Start quietly - for init scripts.

-v, --verbose

Print debug info.

-V, --version

Print the version number and exit.

-r, --realtime

Start with realtime priority (i.e. use the round-robin scheduler). This requires nullmodem to run with root privileges.

-m, --memorylock

Lock the executable of nullmodem to RAM. This keeps nullmodem from being swapped out.

--setuid n

Set the UserID (UID) of the pseudo terminal spacial files to n.

--setgid n

Set the GroupID (GID) of the pseudo terminal spacial files to n.


Use blocking IO to handle the interfaces (default: NONBLOCKing).


Juergen Rinas <>

See Also

kissnetd(8), openpty(3)


JULY 2004 Linux User Manuals