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Add a command (~D) to drop the DTR line for a second (similar to using
~# for a BREAK). This is useful as it makes some microcontroller boards
reset. From Visa Hankala.

.\"	$OpenBSD: cu.1,v 1.7 2012/07/15 06:55:28 nicm Exp $
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.\"	@(#)tip.1	8.4 (Berkeley) 4/18/94
.\"
.Dd $Mdocdate: July 15 2012 $
.Dt CU 1
.Os
.Sh NAME
.Nm cu
.Nd serial terminal emulator
.Sh SYNOPSIS
.Nm
.Op Fl l Ar line
.Op Fl s Ar speed \*(Ba Fl Ar speed
.Sh DESCRIPTION
.Nm
is used to connect to another system over a serial link.
In the era before modern networks, it was typically used to
connect to a modem in order to dial in to a remote host.
It is now frequently used for tasks such as attaching to the
serial console of another machine for administrative or
debugging purposes.
.Pp
The options are as follows:
.Bl -tag -width 4n
.It Fl l Ar line
Specify the line to use.
Either of the forms like
.Pa tty00
or
.Pa /dev/tty00
are permitted.
The default is
.Pa /dev/cua00 .
.Pp
For reasons outlined in
.Xr tty 4 ,
.Xr cua 4
devices should be used on architectures which have them.
For those which do not,
.Xr tty 4
devices can be used.
Users in group
.Dq dialer
are permitted to use
.Xr cua 4
devices by default;
permissions on
.Pa /dev/tty00
or
.Pa /dev/ttya
can be changed,
but they will revert to their defaults
after an upgrade or (re)install.
.It Fl s Ar speed \*(Ba Fl Ar speed
Set the speed of the connection.
The default is 9600.
.El
.Pp
Typed characters are normally transmitted directly to the remote
machine (which does the echoing as well).
A tilde
.Pq Ql ~
appearing as the first character of a line is an escape signal; the
following are recognized:
.Bl -tag -offset indent -width Fl
.It Ic ~^D No or Ic ~.
Drop the connection and exit.
Only the connection is dropped \(en the login session is not terminated.
.It Ic ~\*(Gt
Copy file from local to remote.
.Nm
prompts for the name of a local file to transmit.
.It Ic ~$
Pipe the output from a local
.Ux
process to the remote host.
The command string sent to the local
.Ux
system is processed by the shell.
.It Ic ~#
Send a
.Dv BREAK
to the remote system.
.It Ic ~^Z
Stop
.Nm
(only available with job control).
.It Ic ~C
Fork a child process on the local system to perform special protocols
such as XMODEM.
The child program will be run with the following arrangement of
file descriptors:
.Bd -literal -offset indent
0 \*(Lt-\*(Gt remote tty in
1 \*(Lt-\*(Gt remote tty out
2 \*(Lt-\*(Gt local tty stderr
.Ed
.It Ic ~D
Deassert the data terminal ready (DTR) line briefly.
.It Ic ~R
Record all output from the remote system to a file.
If the given file already exists, it is appended to.
If no file is specified, any existing recording is stopped.
.It Ic ~S
Change the speed of the connection.
.It Ic ~X
Send a file with the XMODEM protocol.
.It Ic ~?
Get a summary of the tilde escapes.
.El
.Pp
When
.Nm
prompts for an argument, for example during setup of a file transfer,
the line typed may be edited with the standard erase and kill characters.
A null line in response to a prompt, or an interrupt, will abort the
dialogue and return the user to the remote machine.
.Pp
.Nm
guards against multiple users connecting to a remote system by opening
modems and terminal lines with exclusive access.
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
This version was written for
.Ox 5.2
by Nicholas Marriott.