ESXi supports the detection and configuration of headless systems.

A headless system is a system that can be operated without a monitor, keyboard, or mouse. Network Appliance boxes do not have Video Graphics Array (VGA), the primary interface is a single serial port. You can set up your existing headless systems to use ESXi. You can add ESXi appliances to a data center where virtual machines are managed with vCenter Server. All existing ESXi features can be used with a headless system that is configured with either embedded flash or minimal local storage. ESXi allows for dynamic switching between different serial modes, which is useful for diagnosing and debugging problems. You can switch between modes to view or modify system parameters.

How to Detect a Headless System

ESXi automatically detects headless systems.

ESXi automatically redirects the DCUI over a serial port connection to improve headless detection. When ESXi automatically detects a headless system, ESXi will set up the serial port as COM1, 115200 baud, and redirects the DCUI over this serial port. The specific settings of com port and baud rate are read from the Serial Port Console Redirection (SPCR) table, if it exists. This behavior can be deactivated using new boot parameters if the default settings are not acceptable. You can set the headless flag in the ACPI FADT table to mark a system as headless.

Serial Mode Dynamic Switching

ESXi supports dynamic switching between four different serial port modes.

ESXi supports serial mode dynamic switching to provide maximum platform flexibility, and to allow debugging and supportability in the text box. ESXi examines the input characters for any serial port mode and switches the modes based on the input key sequence. DCUI, Shell, GDB, and Logging modes are supported. If you have two serial ports, only one of the four modes is allowed on each port. Two serial ports cannot be in the same mode. If you attempt a dynamic switch to a mode in use by the other serial port, the request is ignored. Dynamic switching eliminates the need to interrupt the boot process manually or to create a custom image to redirect to a serial port. It also addresses supportability issues regarding headless systems that only have one serial port, by making it possible to switch the serial port between different modes of operation.

What Serial Port Modes Does ESXi Support

ESXi supports four serial port modes — logging mode, GDB mode, Shell mode, and DCUI mode.

There are four serial port modes in ESXi:

Logging mode – Logging mode is the default mode in a debug build. Logging mode sends the vmkernel.log over the serial port.

GDB mode – Use GDB mode for dedicated debugging.

Shell mode – Shell mode is the shell port access, which is similar to SSH.

DCUI mode – DCUI mode is a Direct Console User Interface. This is the user interface that is displayed when you boot ESXi using a monitor.

Note:

Only COM1 and COM2 ports are supported. USB serial or PCI serial cards are not supported.

ESXi Keystrokes for Dynamic Serial Mode Switching

ESXi includes a unique keystroke sequence that allows dynamic serial mode switching.

Dynamic Switching Keystrokes

Once the correct keystroke sequence is entered, the system switches the serial port to the desired mode.

Logging mode: Ctrl+G, Ctrl+B, 1

Shell mode: Ctrl+G, Ctrl+B, 2

DCUI mode: Ctrl+G, Ctrl+B, 3

GDB mode: Ctrl+G, Ctrl+B, ?

Note: Once in GDB mode, you cannot switch modes again using a key sequence. You must use the CLI to switch modes.

How Do You Switch Serial Modes Through the ESXi CLI

You can switch serial modes using the CLI.

Dynamic Switching Using the CLI

Use esxcfg-advcfg to set the current mode to none. Then set the new desired mode using the CLI.

Logging mode: esxcfg-advcfg -s com1 /Misc/LogPort

Shell mode: esxcfg-advcfg -s com1 /Misc/ShellPort

DCUI mode: esxcfg-advcfg -s com1 /Misc/ConsolePort

GDB mode: esxcfg-advcfg -s com1 /Misc/GDBPort

Example

If the serial mode is set to logging mode, enter these two commands to switch it to DCUI mode.

§. > esxcfg-advcfg –s none /Misc/LogPort

§. > esxcfg-advcfg –s com1 /Misc/ConsolePort

What Are the Keystrokes for Controlling the Serial DCUI

You can use alternate keystrokes to control the DCUI over a serial port. These alternate are useful when F2 or other function keys cannot be used.

Controlling the Serial DCUI

Alternate keystroke mappings for DCUI mode:

  • Esc + 1 -> F1
  • Esc + 2 -> F2
  • Esc + 3 -> F3
  • Esc + 4 -> F4
  • Esc + 5 -> F5
  • Esc + 6 -> F6
  • Esc + 7 -> F7
  • Esc + 8 -> F8
  • Esc + 9 -> F9
  • Esc + 0 -> F10
  • Esc + ! -> F11
  • Esc + @ -> F12