Open serial (COM1) line on Linux to manage a switch through the console

A null-modem cable should work... But in this case, just reset the device to its factory settings.

To execute the factory default reset on the switch, perform these steps:

1. Simultaneously press the Reset and Clear buttons on the front of the switch with a paperclip.
2. Continue to hold the Clear button while releasing the Reset button.
3. When the Self Test LED begins to blink, release the Clear button.

The switch will then complete its self test and begin operating with its configuration restored to the factory default settings.

The switch should also obtain a DHCP address if you have a DHCP server on the network.

Many network devices use the Yost RJ45 pinout for RS-232 console communications. Cisco is probably the best known, but certainly not the only. The switch should have come with a DB9 to RJ45 blue cable. You can just pickup any USB-DB9 Serial adapter (though I highly recommend getting one with a Prolific PL2303HX Rev D Chipset, as they "just work" and are compatible with a wide array of OSes).