.vmsn file - This is the snapshot state file, which stores the exact running state of a virtual machine at the time you take that snapshot.
Log files
Once you understand VM file types, you'll want to become very familiar with log files. Log files are the best method for troubleshooting problems with virtual machines. It's the first place you should check when problems occur.
The most important file is the Vmware.log file. This is the main log file for the VM on the ESX server, and is located in the working directory for the VM. Vmware.log is always the current working log for the VM and older log files are incremented numerically, i.e. vmware-1.log
You should also check /var/log/vmkernel and /var/log/vmware/hostd.log on the ESX host for any errors that may be related to the problem you are experiencing with your VM. Sometimes, restarting the hostd service (service mgmt-vmware restart) on the ESX host will resolve quirky problems with virtual machines. For more common problems, there are more specific techniques that will likely resolve your problem; I'll go over these next.
Problem: Can't shut down a virtual machine
Let's say you can not shutdown a VM using the VM power controls. You can try using command line methods to try and manually kill your stuck VM. There are several methods for doing this below. Employ these methods only as a last resort, short of restarting your ESX host.
Problem: Can't power on a virtual machine
Another common problem may be that you can not power on a VM. This can happen if the host server does not have enough resources for the VM to use. For example, if the VM has a memory reservation set and the ESX host does not have enough physical memory to meet the reservation, then it cannot power on the VM. If this happens you can either remove the memory reservation from the VM and migrate it to another host with more free physical memory, or you can free up physical memory on the existing host.
Also, when a VM is powered on it needs to create a vswp file in the working directory of the VM on the ESX host that is equal to the amount of RAM assigned to the VM (minus any memory reservations). If there is not sufficient disk space on your ESX host, then you will also not be able to power on the VM. A workaround it to set a memory reservation equal to the amount of RAM assigned to the VM so the vswp file will be 0 bytes in size. It's important, however, to always take care to leave additional disk space on your VMFS volumes for things like logs, swap files and snapshots.
Problem: Virtual machine encountering boot errors due to OS corruption
If a VM is having problems while booting due to operating system corruption or faulty configuration, a good way to deal with this is to add its virtual disk to another working VM so you can access the drive and make any needed repairs.
To repair the VM, you should make sure the problem VM is powered off. Next add an additional drive to a working VM and browse to the problem VM's disk file. Boot the working VM; you can now access the drive of the problem VM to make any changes or corrections. When you are done remove the drive from the working VM, add it back to the problem VM and try booting it again.
Problem: General virtual machine OS issues
For troubleshooting problems with the VM's operating system, I create a toolkit of ISO files that contain helpful troubleshooting applications that I can quickly mount on a VM's CD-ROM and use (or boot from) to make repairs to a VM. A few of the ISO files I use include:
Conclusions
These are just a few of the problems and techniques that you will use when troubleshooting virtual machine problems. The information in this article should help you the next time you experience a problem with a troublesome VM.
ABOUT THE AUTHOR: Eric Siebert is a 25-year IT veteran with experience in programming, networking, telecom and systems administration. He is a guru-status moderator on the VMware community VMTN forums and maintains VMware-land.com, a VI3 information site.
