I have a network switch (an HP Procurve) that provides a command line interface that can be accessed via a direct serial port connection. The direct connection is done using an RJ45 connector on the network switch, and a DB9 connector into the serial port on the client computer.
Currently, the switch fault LED is blinking, and the manual indicates that when this happens, one should directly connect to the switch console via a serial connection in order to get more specific debugging information about what is wrong.
So I connect a computer to the network switch using an RJ45-to-DB9 cable. The connecting client computer is running Linux (Debian 8). I then use the
minicom tool as a VT-100 terminal emulator. The Network Switch manual indicates that upon connecting to the console, you need to press enter a few times, and then a welcome message should appear. However, when I start up minicom and press enter 5 to 10 times, nothing happens - i.e. no text appears at all.
What I've tried so far:
First step to debug this was to check what serial ports are available or enabled on the client computer. When I type
dmesg | grep ttyI see that
/dev/ttyS0seems to be available and enabled:
serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
Just to make sure, I tried writing a byte to the serial port, by doing:
echo -en ' ' > /dev/ttyS0
This returned without any error. If I try the same using a different device, like
/dev/ttyS2, I get an
Input/Output error, so this increases my confidence that
/dev/ttyS0is an enabled, valid serial port device.
Secondly, I look in the HP Procurve manual to make sure all the connection settings are correct. The manual indicates that the serial connection should be done using any baud rate from 2400 to 115200, 8 data bits, 1 stop bit, no parity, and flow control set to None. I configure minicom following these settings exactly (with a 9600 baud rate). Minicom specifies settings for both hardware and software flow control (this distinction is not made in the procurve manual) so I set both to None anyway. Finally, I make sure minicom is using
/dev/ttyS0and I save the minicom configuration settings.
So far, the connection still doesn't work. When I start up
minicomand press enter 5 to 10 times, no text appears.
To rule out a potentially bad RJ45-DB9 cable, I try two other RJ45-DB9 cables. Still no text appears when I start
minicomand press enter 5 to 10 times.
I try a few other "wild guess" debugging techniques, like rebooting the switch and also rebooting the client computer. Still doesn't work.
Question: Given everything I've tried, is the most likely problem here something with the Network Switch itself? Could it simply be the switch itself is damaged in some way that has disabled the CLI? Or is there something obvious I'm missing here in terms of configuring a
minicom client to connect to a serial port?