serial port
I am attempting to login from a Linux client to a set top box running Linux via a USB to serial cable. When I power on the device, I can see the init messages scroll past, and I get to the login prompt, like this:
(none) login:
but I cannot login. The cursor stops flashing as if it is receiving input, but there is no response.
My serial port setup is:
Device: /dev/ttyUSB0
Bps: 115200 8N1
Hardware Flow Control: Yes
Software Flow Control: No
Any help would be greatly appreciated!
If you're using the Send Numbers button after typing a decimal number (or several or they could be hexadecimal, etc.), it's sending the character that corresponds to that code. In PuTTY, if you want to send an ASCII 65 (decimal) then you'd type an "A". If you want to send an ASCII 11 (decimal - Vertical Tab) you could press Ctrl-K or hold down the Alt key and type 11 on the numeric keypad.
Without knowing what you're communicating with, what it expects for input, whether you have PuTTY configured properly, etc., that's the best I can do.
After much fiddling around, I finally figured out the right combination of things to use for a fully usable terminal.
/etc/gettytabI got a new USB/Serial cable. This one has the FTDI, rather than the Prolific chipset. This is important since OSX comes with the FTDI drivers in the box, rather than having to install the third party Prolific drivers. This made troubleshooting much easier, since the serial port stopped getting stuck after each experiment, meaning no more reboots to become usable again.
If you're going to try this yourself, the cable I used was the StarTech Industrial USB RS232 Serial Adapter. This was in conjunction with a random DB9/DB25 adapter, and a gender changer since the ports on the back of the terminal are female.
Note: A previous version of this guide suggested using a different cable - this particular cable will let us use the modem port on the terminal, correcting some various display glitches!
This cable should be connected to the MODEM port on the terminal.
Ignore any guide that suggests you use /etc/ttys, since this file is ignored in modern versions of OS X. This would be the way to go on Linux/BSD, but not here.
I was left wondering how to set the terminal type for the login, since as described above, just using the std.19200 that's provided in /etc/gettytab left the terminal set to su for some reason, and nothing worked.
I added a line as follows:
std.ttyUSB:\
:np:im=\r\n:sp#57600:tt=vt220:
This sets the login banner to a simple CRLF, sets the line speed to 57600 baud, and most importantly, sets the terminal to vt220. This will become important later.
Now we need to actually start this. As described elsewhere, you can't just run getty, since that's restricted to launchd. We have to make and load a daemon plist.
To /Library/LaunchDaemons, I added a serialconsole.plist with the following contents:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>KeepAlive</key>
<true/>
<key>Label</key>
<string>serialconsole</string>
<key>ProgramArguments</key>
<array>
<string>/usr/libexec/getty</string>
<string>std.ttyUSB</string>
<string>cu.usbserial-AI02GVBH</string>
</array>
</dict>
</plist>
If you do this yourself, the third string will almost certainly be different, since this is the serial number of the adapter. The second line references the line we just added to to /etc/gettytab. Also note the setting of KeepAlive to true - this means that when the process exits (say, we log out), a new instance will spawn. Without this, you have to manually start the job.
Finally, the terminal itself has to be configured. This is a Wyse WY50, but it can emulate many other terminal types. I find that VT220 mode gives the best experience.
To enter setup mode on the terminal from factory settings, hit Shift + Setup.
Pressing F1 to enter the DISP menu, I set:
F2 to the General screen.
F3 to the KEYCODE screen
F4 to the COMM screen
More super important stuff:
One more - F5 to the PORTS screen
Everything else I left at factory defaults.
Hit F12, then Space to set Save to Yes, and then F12 once more to save settings.
We're ready to go. Make sure the terminal is on and plugged in to the port, verify the settings are as described above both gettytab and the plist file you created.
We load the created plist into launchd:
launchctl load -w /Library/LaunchDaemons/serialconsole.plist
And finally start it:
launchctl start serialconsole.plist
And in a moment, you should have a login prompt on your terminal! Some photos:
You might notice that certain applications still write garbage onto the screen, especially if they do anything fancy like bold text or certain ASCII characters. Most recent machines, macs included, use UTF-8 for their character set. But this venerable glass terminal has no idea what that is! You'll need to set the locale to the appropriate legacy codepage for your region. In the USA, this is en_US.ISO-8859-1. Have a look at the output of locale, and work the command export LC_ALL='en_US.ISO-8859-1' into a login script that checks your $TERM variable. You really don't want to set this system wide, but only on sessions where your glass terminal is being used.
Best Answer
Without knowing either your set-top box or your cable, I would first try disabling hardware flow control, since the set top probably doesn't implement it. Essentially your Linux client is waiting for an "OK to send" signal that it will never receive because there's no physical wire in the set top to send it.