VMware Tools without a reboot?

Every now and then, you see blogposts appearing on the "issue" that you need to reboot a guest operating system after you install or update the VMware Tools. Many people have pondered about whether a reboot is in fact really necessary and if it can be avoided all together. Recent posts about this can be read here and here, refering to this VMware community thread -- the question is still alive in multiple-year spanning threads like this one right here. I usually frown my eyebrowses when reading on these "no reboot" topics, yet I am interested in keeping up with the advancements in that subject for some of the large customers that I come in contact with professionaly.

The scripts and methods outlined in these blogposts sound a bit tricky at first if you ask me, and I feared they might not have the outcome you expected. I would think the VMware tools really require a reboot on some operating systems because you update parts of the virtual device drivers and those need to be reloaded by a reboot of the operating system (Note: strictly speaking you don't need a reboot for all types of device drivers, only under a specific set of circumstances documented by Microsoft. The VMware disk drivers host a boot device so that would fit under the "requires a reboot" category from that document). This means that just running the installer with a "Suppress Reboot" parameter on all your machines will place the new VMware Tools files on your harddisk, but will not actively load all of them... I am not sure if that is a state I would want my production virtual machines in!? And to be very clear: what these scripts do is request an automatic postpone of the reboot, not trigger some hidden functionality in VMware Tools not to really reboot after all!

To remove all suspicion, I did a little test on a Windows 2003 virtual machine and upgraded the tools from ESX 3.0.2 to ESX 3.5U2 without rebooting (using the commandline setup.exe /S /v"REBOOT=R /qb" on the VMware Tools ISO). This effectively updates the following services and drivers without rebooting:

• VMware services (bumped from build 63195 to build 110268)
• VMware SVGA II driver, VMware Pointing Device driver

It left the following drivers untouched:

• VMware Virtual disk SCSI Disk Device ("dummy" harddisk driver - Microsoft driver)
  
• NECVMWar VMware IDE CDR10 (virtual CD-ROM driver)
• Intel Pro/1000 MT Network Connection (vmnet driver - Microsoft driver)
• LSI Logic PCI-X Ultra320 SCSI Host Adapter (storage adapter - Microsoft driver)

It turned out that these drivers didn't require updating for my specific virtual machine (even after a reboot). In fact, I wasn't immediatelly able to find one machine in the test environment at work that required updating any bootdisk device drivers (and some still had 3.0.2 VMware Tools running!).

To conclude, I would say that in some circumstances it is safe to postpone the reboot of your virtual machine, if at minimum the boot disk device drivers are not touched. Postponing the reboot is very convenient if you use it in the context of a patch weekend where you want to postpone the restart to one big, single reboot at the end of all your patches.

Update: as Duncan Epping points out in a recent blogpost, be also advises that updating the network driver effectively drops all network connections. This is for all practical purposes maybe just as bad as actually rebooting your server, so beware with the "fake level of safety and comfort" that you might have by postponing a VMware Tools reboot!