Cisco's SF/SG 300/500 series managed switches have CLI access via Telnet and SSH but this is turned off by default, leaving only the web interface to manage the switch. You can enable Telnet and/or SSH via the web interface, enabling management via CLI.

1. Log on to the web interface, then navigate to Security → TCP/UDP Services.
2. Check the Enable boxes for Telnet Service and/or SSH Service. You can check both if you wish to enable both protocols. Click Apply, which will immediately start the selected services:
   
3. Don't forget to save the configuration change to flash. Otherwise, the change will be lost after a reboot: