If you wish to execute a command in all running Containers, you can use the following script:

for i in `cat /proc/vz/veinfo | awk '{print $1}'|egrep -v '^0$'`; \
do echo "Container $i"; vzctl exec $i <command>; done

where <command> is the command to be executed in all the running Containers. For example:

for i in `cat /proc/vz/veinfo | awk '{print $1}'|egrep -v '^0$'`; \
do echo "Container $i"; vzctl exec $i uptime; done

Container 1
2:26pm up 6 days, 1:28, 0 users, load average: 0.00, 0.00, 0.00
Container 101
2:26pm up 6 days, 1:39, 0 users, load average: 0.00, 0.00, 0.00

Source: http://download.swsoft.com/virtuozzo/virtuozzo4.0/docs/en/lin/VzLinuxUG/260.htm