COMCONTROL(8) MidnightBSD System Manager’s Manual COMCONTROL(8)


comcontrol — control a special tty device


comcontrol special_device [dtrwait number] [drainwait number]


The comcontrol utility is used to examine and modify some of the special characteristics of the specified tty device. If no arguments other than the device (or "-" for stdin) are specified, it prints the settings of all controllable characteristics. This usage requires only read access on the device. Only the superuser can change the settings.

The following options are available:

dtrwait number

Set the time to wait after dropping DTR to the given number. The units are hundredths of a second. The default is 300 hundredths, i.e., 3 seconds. This option needed mainly to set proper recover time after modem reset.

drainwait number

Set the time to wait for output drain to the given number. The units are seconds. The default is 5 minutes, 0 means waiting forever. This option needed mainly to specify upper limit of minutes to prevent modem hanging.

The standard way to use comcontrol is to put invocations of it in the /etc/rc.d/serial startup script.


dialin devices, hardwired terminals


dialout devices


stty(1), sio(4)


Originally part of cgd’s com package patches, version 0.2.1, to 386BSD 0.1. Once controlled bidirectional capabilities. Little is left to control now that these capabilities are standard.


Christopher G. Demetriou

MidnightBSD 0.3 May 15, 1994 MidnightBSD 0.3