Logs for an ESXi 5.1 host are grouped according to the source component:
/var/log/auth.log: ESXi Shell authentication success and failure.
/var/log/dhclient.log: DHCP client service, including discovery, address lease requests and renewals.
/var/log/esxupdate.log: ESXi patch and update installation logs.
/var/log/lacp.log: Link Aggregation Control Protocol logs.
/var/log/hostd.log: Host management service logs, including virtual machine and host Task and Events, communication with the vSphere Client and vCenter Server vpxa agent, and SDK connections.
/var/log/hostd-probe.log: Host management service responsiveness checker.
/var/log/rhttpproxy.log: HTTP connections proxied on behalf of other ESXi host webservices.
/var/log/shell.log: ESXi Shell usage logs, including enable/disable and every command entered.
/var/log/sysboot.log: Early VMkernel startup and module loading.
/var/log/syslog.log: Management service initialization, watchdogs, scheduled tasks and DCUI use.
/var/log/usb.log: USB device arbitration events, such as discovery and pass-through to virtual machines.
/var/log/vob.log: VMkernel Observation events, similar to
/var/log/vmkernel.log: Core VMkernel logs, including device discovery, storage and networking device and driver events, and virtual machine startup.
/var/log/vmkwarning.log: A summary of Warning and Alert log messages excerpted from the VMkernel logs.
/var/log/vmksummary.log: A summary of ESXi host startup and shutdown, and an hourly heartbeat with uptime, number of virtual machines running, and service resource consumption.
/var/log/Xorg.log: Video acceleration.
Note: For information on sending logs to another location (such as a datastore or remote syslog server).
When an ESXi 5.1 host is managed by vCenter Server 5.1, two components are installed, each with its own logs:
/var/log/vpxa.log: vCenter Server vpxa agent logs, including communication with vCenter Server and the Host Management hostd agent.
/var/log/fdm.log: vSphere High Availability logs, produced by the fdm service.