VT-x is being used by another hypervisor .. Please disable the KVM

while starting my VM using vagrant, I have following error :

The guest machine entered an invalid state while waiting for it
to boot. Valid states are ‘starting, running’. The machine is in the
‘poweroff’ state. Please verify everything is configured
properly and try again.

If the provider you’re using has a GUI that comes with it,
it is often helpful to open that and watch the machine
, since the
GUI often has more helpful error messages than Vagrant can retrieve.
For example, if you’re using VirtualBox, run `vagrant up` while the
VirtualBox GUI is open.

So, I edit my Vagrantfile and uncomment gui

   config.vm.provider "virtualbox" do |vb|
     vb.gui = true

Then I start my vm using VirtualBox. I have the following error :
VT-x is being used by another hypervisor … Please disable the KVM

what to do ?
1. see if kvm is running and is used

witr@serv:~$ lsmod | grep kvm
kvm_intel 143592 3
kvm 459835 1 kvm_intel

here kvm is used by one consumer (kvm_intel) and kvm_intel is used by 3 consumers.

2. stop kvm consumers
In my case it’s the android emulator i have launched from AndroidStudio which causes problem. I stop emulator.

3. restart vm
that’s all

target busy when umount

I have mount webdav directory /mnt/wdav (more). And, now, I want to umount it.
but i have following error:

umount: /mnt/wdav: target is busy
(In some cases useful info about processes that
use the device is found by lsof(8) or fuser(1).)

first step : find out processes using this mount

witr$ fuser -u /mnt/wdav
/mnt/wdav: 408c(witr)

second step : identify process

witr$ ps 408
408 pts/33 Ss 0:00 /opt/appli

third step : stop process

witr$ fuser -k /mnt/wdav

last step : safe umount

witr$ sudo umount /mnt/wdav

recover lost centos 5&6 root password

1. Reboot
2. Press any key after reboot when boot countdown, to go to GRUB menu
3. From that menu, select the appropriate kernel version and press the ‘e’ key
4. Then select the kernel /vmlinuz-… line and press the ‘e’ key
5. At the end of displayed line type space and then type 1 (you can type ‘s’ or ‘single’ rather than ‘1’). Press Enter to save changes
6. You should already be on the kernel /vmlinuz… line. Press the ‘b’ key to boot to these temporary options to allow you to recover your root password
7. When prompted type ‘passwd’ and press enter. You will be prompted to type new password twice
8. After typing new password and confirming it, type ‘reboot’ command.

Got from here