A uart is a 16550 or 8260 chip, so just use dmesg to look at what you have available on your computer
dmesg | grep tty
[ 1.534394] printk: console [tty0] enabled
[ 2.130401] 00:02: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A
[ 2.151509] 00:03: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
so from above, now you'll be able find 2 serial ports under /dev at /dev/ttyS0 and /dev/ttyS1
When you only have a CLI, install the minicom terminal application. Then configure it for your serial port. I've configured mine to talk to a Cisco switch on /dev/ttyS1 (rear serial port of Dell R720XD).
press CTRL + A, then x to exit the terminal application
apt-get install minicom
minicom -s
+-----------------------------------------------------------------------+
| A - Serial Device : /dev/ttyS1 |
| B - Lockfile Location : /var/lock |
| C - Callin Program : |
| D - Callout Program : |
| E - Bps/Par/Bits : 9600 8N1 |
| F - Hardware Flow Control : No |
| G - Software Flow Control : No |
| H - RS485 Enable : No |
| I - RS485 Rts On Send : No |
| J - RS485 Rts After Send : No |
| K - RS485 Rx During Tx : No |
| L - RS485 Terminate Bus : No |
| M - RS485 Delay Rts Before: 0 |
| N - RS485 Delay Rts After : 0 |
| |
| Change which setting? |
+-----------------------------------------------------------------------+