We need vzdump, but isn't there in Ubuntu 8.04 repository, so download from proxmox site and install by hand, but first the dependencies

aptitude install liblockfile-simple-perl cstream ssmtp

I find that dont work anymore the download, so i searched manually on the Ubuntu repos, then i have manually uploaded

cd /tmp
# wget http://www.proxmox.com/cms_proxmox/cms/upload/vzdump/vzdump_1.1-1_all.deb
dpkg -i vzdump_1.2.4-2_all.deb

To create a dump in the default folder (/vz/dump or /var/lib/vz/dump), use

vzdump --compress --stop 1101

To not stop, but suspend the VM, that have a minor down time, use

vzdump --compress --suspend 1101

After the backup, take a look at the dump directory…

ls -l /vz/dump/