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Old 02-26-2012, 11:48 PM   #1
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SSH to servers via Serial to USB

I am trying to set up out of band access from an access server running Ubuntu to a FreeBSD server and a CentOS server. Does anyone know if there is a way to SSH from the Ubuntu server via its serial port to each machine's USB ports as follows:

Ubuntu Serial Port->Serial-to-USB Cable->FreeBSD machine USB Port

Ubuntu Serial Port->Serial-to-USB Cable->CentOS machine USB Port

Any help would be greatly appreciated!

Old 02-27-2012, 03:29 AM   #2
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well you couldn't SSH to it without having a network link across it, which sounds like over kill to me. Additionally if that is a tcp/ip link, does that not make it implicitly "in band" again? do you get a serial device on the USB side? You'd want to start a tty (mgetty or agetty on centos I think) on ttyS0 or whatever device you get, and then use a console client, kermit for example, to connect.
Old 02-27-2012, 05:33 PM   #3
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slip connection?
Old 02-28-2012, 12:42 AM   #4
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To acid_kewpie: When you ask "do you get a serial device on the USB side?" are you asking if there are serial ports on the centos and FreeBSD machines I want to access through my Access Server running Ubuntu. If so, I believe the answer is yes. The reason I am using an RS232 to USB cable is because I was thinking of using Ser2Net on the Ubuntu server...but from what I read about Ser2Net, I'd have to be doing it backwards, USB on my Ubuntu machine to the serial ports on the Centos and FreeBSD and then access the machines via telnet. I thought about going this route because the serial to usb cables is what I found in my supply bag. Otherwise, I'd be using a null modem cable. It looks like if I go this route, I will still have to follow your advise on starting a tty on both machines by their OS/Kernel rules. Let me play with it and if I have any more questions, I will ask. Either way I thank you for your response. I really appreciate your advise and input.

To jefro: Thank you for your response too. If I had the null modem cables, I'd use the SLIP protocol, but I don't have them. I am gonna try acid_kewpie's advise on starting tty on the machines' serial ports and reverse the connections of the RS232 to USB cable and see if I can use the Ser2Net daemon to allow me to telnet to each machine.

Succes or Fail, I'll let you felas know!
Old 03-02-2012, 03:05 PM   #5
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Still Trying...


The following are the servers and the ports in question:
Access Server: Ubuntu - the serial port where serial-to-USB is connected is ttyS5
Target Server: Centos - the USB port where Serial-to-USB is connected is ttyUSB0

When I unplugged the serial-to-USB cable, I got this entry in the dmesg output:
usb 1-1: USB disconnect, address 14

When connect it, I get this in the dmesg output:
usb 1-1: pl2303 converter now attached to ttyUSB0


**NOTE: I don't have a null modem cable, all I have at this time is a serial-to-usb cable.**

I am trying to use ser2net. The configuration, /etc/ser2net.conf file has the following:

2000:telnet:600:/dev/ttyS5:115200 8DATABITS NONE 1STOPBIT banner

According to the documentation, it is supposed to allow me to start a session on the Target Server from the Access Server the following


//this is on the Access Server:
#telnet localhost 2000

Trying ::1...
telnet: Unable to connect to remote host: Connection refused

I already checked the firewall settings on the Target Server and made sure the telnet service was working. I tested this by initiating a regular telnet session from the Access Server's telnet client to the target server's telnet service. It works with no problems.

Am I supposed to somehow make sure that the telnet service on the Target Server is listening on the USB port of ttyUSB0? Should I
spawn ttyUSB0 to allow a remote telnet login or something similar? Please advise.

Thanks in advance!



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