How can I determine when a serial terminal has (dis)connected?
Clash Royale CLAN TAG#URR8PPP
I have a DEC VT101 serial terminal hooked up to a Raspberry Pi 3 running Debian using a USB RS-232 null modem cable. When I turn the terminal off, I would like for the shell session to end, and when I turn the terminal back on, I'd like that to start a new login session. How can I do this? Right now, when the terminal is turned off then back on, the screen remains blank until I do something e.g. press Return which will make Bash draw a new prompt.
At the very least, if I could figure out how to query whether there was a system receiving the data from the USB null modem cable, I could script the automatic logging in/out myself. One approach I have in mind would be to send answerback queries to the terminal when there has been no recent user input then assume the terminal is off if I don't get a response after a certain amount of time.
shell terminal getty
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
add a comment |
I have a DEC VT101 serial terminal hooked up to a Raspberry Pi 3 running Debian using a USB RS-232 null modem cable. When I turn the terminal off, I would like for the shell session to end, and when I turn the terminal back on, I'd like that to start a new login session. How can I do this? Right now, when the terminal is turned off then back on, the screen remains blank until I do something e.g. press Return which will make Bash draw a new prompt.
At the very least, if I could figure out how to query whether there was a system receiving the data from the USB null modem cable, I could script the automatic logging in/out myself. One approach I have in mind would be to send answerback queries to the terminal when there has been no recent user input then assume the terminal is off if I don't get a response after a certain amount of time.
shell terminal getty
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
add a comment |
I have a DEC VT101 serial terminal hooked up to a Raspberry Pi 3 running Debian using a USB RS-232 null modem cable. When I turn the terminal off, I would like for the shell session to end, and when I turn the terminal back on, I'd like that to start a new login session. How can I do this? Right now, when the terminal is turned off then back on, the screen remains blank until I do something e.g. press Return which will make Bash draw a new prompt.
At the very least, if I could figure out how to query whether there was a system receiving the data from the USB null modem cable, I could script the automatic logging in/out myself. One approach I have in mind would be to send answerback queries to the terminal when there has been no recent user input then assume the terminal is off if I don't get a response after a certain amount of time.
shell terminal getty
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
I have a DEC VT101 serial terminal hooked up to a Raspberry Pi 3 running Debian using a USB RS-232 null modem cable. When I turn the terminal off, I would like for the shell session to end, and when I turn the terminal back on, I'd like that to start a new login session. How can I do this? Right now, when the terminal is turned off then back on, the screen remains blank until I do something e.g. press Return which will make Bash draw a new prompt.
At the very least, if I could figure out how to query whether there was a system receiving the data from the USB null modem cable, I could script the automatic logging in/out myself. One approach I have in mind would be to send answerback queries to the terminal when there has been no recent user input then assume the terminal is off if I don't get a response after a certain amount of time.
shell terminal getty
shell terminal getty
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
asked Feb 4 at 7:23
Eric PruittEric Pruitt
1012
1012
add a comment |
add a comment |
1 Answer
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The usual way of doing this was by detecting when the DTR ("data terminal ready") signal drops. This does require more than just ground, receive data and transmit data to be wired up.
The stty settings have to be adjusted to not ignore the DTR signal. Try running stty -clocal. If your connection is immediately dropped, then your cable does not have the appropriate pins connected. If you still have a shell connection after running the stty command, then try turning the terminal off and on. I would expect the session to be killed then. If not, then it's possible that your serial cable loops the DSR ("data set ready") signal coming out of the RS232 adapter back into its DTR input; you can test this by removing the cable from the adapter and see if that logs you out. If so, then you need to rewire the serial cable.
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
Runningstty -clocaldidn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.
– Eric Pruitt
Feb 9 at 7:11
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
add a comment |
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1 Answer
1
active
oldest
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The usual way of doing this was by detecting when the DTR ("data terminal ready") signal drops. This does require more than just ground, receive data and transmit data to be wired up.
The stty settings have to be adjusted to not ignore the DTR signal. Try running stty -clocal. If your connection is immediately dropped, then your cable does not have the appropriate pins connected. If you still have a shell connection after running the stty command, then try turning the terminal off and on. I would expect the session to be killed then. If not, then it's possible that your serial cable loops the DSR ("data set ready") signal coming out of the RS232 adapter back into its DTR input; you can test this by removing the cable from the adapter and see if that logs you out. If so, then you need to rewire the serial cable.
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
Runningstty -clocaldidn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.
– Eric Pruitt
Feb 9 at 7:11
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
add a comment |
The usual way of doing this was by detecting when the DTR ("data terminal ready") signal drops. This does require more than just ground, receive data and transmit data to be wired up.
The stty settings have to be adjusted to not ignore the DTR signal. Try running stty -clocal. If your connection is immediately dropped, then your cable does not have the appropriate pins connected. If you still have a shell connection after running the stty command, then try turning the terminal off and on. I would expect the session to be killed then. If not, then it's possible that your serial cable loops the DSR ("data set ready") signal coming out of the RS232 adapter back into its DTR input; you can test this by removing the cable from the adapter and see if that logs you out. If so, then you need to rewire the serial cable.
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
Runningstty -clocaldidn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.
– Eric Pruitt
Feb 9 at 7:11
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
add a comment |
The usual way of doing this was by detecting when the DTR ("data terminal ready") signal drops. This does require more than just ground, receive data and transmit data to be wired up.
The stty settings have to be adjusted to not ignore the DTR signal. Try running stty -clocal. If your connection is immediately dropped, then your cable does not have the appropriate pins connected. If you still have a shell connection after running the stty command, then try turning the terminal off and on. I would expect the session to be killed then. If not, then it's possible that your serial cable loops the DSR ("data set ready") signal coming out of the RS232 adapter back into its DTR input; you can test this by removing the cable from the adapter and see if that logs you out. If so, then you need to rewire the serial cable.
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
The usual way of doing this was by detecting when the DTR ("data terminal ready") signal drops. This does require more than just ground, receive data and transmit data to be wired up.
The stty settings have to be adjusted to not ignore the DTR signal. Try running stty -clocal. If your connection is immediately dropped, then your cable does not have the appropriate pins connected. If you still have a shell connection after running the stty command, then try turning the terminal off and on. I would expect the session to be killed then. If not, then it's possible that your serial cable loops the DSR ("data set ready") signal coming out of the RS232 adapter back into its DTR input; you can test this by removing the cable from the adapter and see if that logs you out. If so, then you need to rewire the serial cable.
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
answered Feb 4 at 8:29
wurtelwurtel
10.5k11526
10.5k11526
Runningstty -clocaldidn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.
– Eric Pruitt
Feb 9 at 7:11
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
add a comment |
Runningstty -clocaldidn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.
– Eric Pruitt
Feb 9 at 7:11
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
Running
stty -clocal didn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.– Eric Pruitt
Feb 9 at 7:11
Running
stty -clocal didn't kill the connection. Rewiring the cable isn't a practical solution for me right now, so I can't personally test this answer out. I'll request this question be converted to a community wiki if I don't get any other responses.– Eric Pruitt
Feb 9 at 7:11
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
This post helped me refine my Googling, and I came across stackoverflow.com/questions/25232237/… which has additional details. I was able to find the type of cable I need searching for "full handshake." I'll follow-up once I receive cable and have time to test it out.
– Eric Pruitt
Feb 10 at 1:30
add a comment |
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