The ESXi Shell (formerly Tech Support Mode or TSM) is disabled by default on ESXi. You can enable local and remote access to the shell if necessary.

Enable the ESXi Shell for troubleshooting only. The ESXi Shell can be enabled and disabled whether or not the host is running in lockdown mode.

ESXi Shell
Enable this service to access the ESXi Shell locally.
Enable this service to access the ESXi Shell remotely using SSH.
Direct Console UI (DCUI)
When you enable this service while running in lockdown mode, you can log in locally to the direct console user interface as the root user and disable lockdown mode. You can then access the host using a direct connection to the vSphere Client or by enabling the ESXi Shell.

The root user and users with the Administrator role can access the ESXi Shell. Users who are in the Active Directory group ESX Admins are automatically assigned the Administrator role. By default, only the root user can execute system commands (such as vmware -v) using the ESXi Shell.

Note: Do not enable the ESXi Shell until it is required.