If you use Vagrant with KVM Libvirt , there is a high chance that you are annoyed by the  password prompts for every Vagrant commands e.g. vagrant up/ssh/destroy unless you are running the commands as root.

The issue is that the a typical Linux user does not have access permission to libvirt socket so to access it we need to provide extra permission.  Interestingly libvirt uses Policy Kit ( man polkit) to decide access permissions and we can add an explicit rule to polkit to give an user privilege to access libvirt.

To fix the issue you need to create a file in /etc/polkit-1/localauthority/50-local.d as mentioned below.

There are other methods to fix this issue too. You can also create a user group, give the group privilege and add the user to the group.

# cd  /etc/polkit-1/localauthority/50-local.d
# cat vagrant.pkla 
[Allow lmohanty libvirt management permissions]
Identity=unix-user:<USER_NAME>
Action=org.libvirt.unix.manage
ResultAny=yes
ResultInactive=yes
ResultActive=yes

References
[1] https://niranjanmr.wordpress.com/2013/03/20/auth-libvirt-using-polkit-in-fedora-18/
[2] https://ttboj.wordpress.com/2013/12/09/vagrant-on-fedora-with-libvirt/