man vzdump
...
CONFIGURATION
Global configuration is stored in /etc/vzdump.conf.
tmpdir: DIR
dumpdir: DIR
storage: STORAGE_ID
mode: snapshot|suspend|stop
bwlimit: KBPS
ionize: PRI
lockwait: MINUTES
stopwait: MINUTES
size: MB
maxfiles: N
[B]script: FILENAME[/B]
exclude-path: PATHLIST
HOOK SCRIPT
You can specify a hook script with option "--script". [B]This script is called at various phases[/B] of the backup process, with parameters accordingly set. You can
find an example in the documentation directory ("vzdump-hook-script.pl").