I'm trying to compress a virtual machine image file through a script, but I want to be sure the file isn't being accessed. I could check if virt-manager is running, since it should be the only program accessing the image, but I don't know if there's a better way to do it. I also want the script to continue trying until the file is available to compress. I don't know how do to that either.

#Check if virt-manager is running
if pgrep "virt-manager" > /dev/null
then
    #re-run script until success
else
    gzip -k < /home/brady/.vms/windows10/hdd.img > /media/backup/vms/windows10/hdd.$(date +"%F.%T).img.gz