What makes an ESXi?

Just exactly what makes up an ESXi?

  • There is no Service Console rather has VMKernel and VMM
  • Traditional command line interface with access to Management, Troubleshooting, and Config Tools is gone
  • Third Party agents, Backups, customized settings to be applied differently

ESXi has three components

VMKernel: It’s a 64 bit Microkernel OS POSIX styled oS, desinged by VMware to be not a general purpose OS but one specifically tuned to operate as a hypervisor

VMKernel Extensions: It involves special kernel modules and device drivers which help the OS interact with the hardware


System Worlds:

Processes like idle and helper run as system worldsVMM worlds: Let’s the guest oS see its own x86 virtualized hardware. Each VM runs on its own scheduled VMM world

User worlds: They can make system calls to the VMkernel to interact with VMs or the system itself

ESXi Agents:

DCUI: Yellow interface that lets you set basic configuration, permit access and restart management agents

CIM Broker: Common Information Model, provides agentless access to hardware monitoring via an externally accessible API

TSM: Technical Support mode to run some command line tools which was present is Service Console

Let’s now talk about the ESXi Flavors i.e. Installable and Embedded

ESXi Installable:

  • ESXi can boot from CD, PXE, USB local storage, Local disk, FC or iSCSI SAN (private LUN). The Image files can reside on CD, USB, FTP, HTTP, HTTPS and NFS export. But boot from NFS is not supported
  • Installation can either be Interactive or using a Kick Start file which can be stored on CD, USB, FTP, HTTP, HTTPS or NFS export
  • System Image can be deployed to Local Harddisk or USB, since 4.1 it can be on SAN LUN (FC, FCoE or iSCSI). iSCSI LUN if you are using NIC that supports iBFT (iSCSI Boot Firmware Table)
  • The Scratch Partition is a 4GB vFAT partition created by default if a local disk is found on the 1st boot. It captures the running state files such as Logs, coredumps etc.

ESXi Emebedded: A version of ESXi that is preinstalled as firmware in the factory or burned to a USB flash drive and installed in an Internal USB Socket on the Main system board.
What different tools are available to manage ESXi:

vSphere Client: Connect directly to the hosts

vCenter: Add the hosts to the vCenter and take advantage of DRS, host profile, Storage DRS etc.

vCLI: vCLI is a Perl Based set of scripts that mimics most of the commands available at the ESX console. The esxcfg- prefix has been renamed to vicfg- prefix

vMA: vSphere Management Assistant is a small just enough OS prepackaged linux virtual Appliance which has preinstalled vCLI. It can also be used as a syslog server

PowerCLI: Run PowerShell Scripts against vCenter inventory objects such as Hosts, VM’s, Storage, Network etc

vSphere Update Manager: Patching/Upgrading ESXi hosts

DCUI: Yellow interface that lets you set basic configuration, permit access and restart management agents

TSM:  Technical Support mode to run some command line tools which was present is Service Console. It is based on small executable called BusyBox (www.busybox.net)

Host Profiles: Used to apply customized settings on all the hosts at a time. It also helps check the compliance of a host and Cluster

Local Authentication: Can have local users with root privileges

Lockdown Mode: Disables all users from accessing the ESXi host, only root can access using DCUI and vpxuser can access the hosts using vCenter. It also affects the CIM access to get the hardware info, instead needs a ticket from vCenter so that the vpxuser can fetch the information. Do not enable the lockdown mode from the DCUI it restricts access to the local users rather do it from the vCenter

Logging: Many of the logs are combined into 3 files

  • VMkernel /var/log/messages (containes hostd log as well)
  • Management Daemon: /var/log/vmware/hostd.log
  • vCenter Agent: /var/log/vmware/vpxa.log


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