ovz-install: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/ovz-install - from package: koan

You may install the required package with command yum install {package}
Error in other languages:
ovz-install: bevel nie gevind nie
ovz-install: comandă negăsită
ovz-install: comando não encontrado
ovz-install: commande introuvable
ovz-install: command not found
ovz-install: käsku ei ole
ovz-install: không tìm thấy lệnh
ovz-install: komanda nerasta
ovz-install: Kommando nicht gefunden.
ovz-install: kommandot finns inte
ovz-install: komut yok
ovz-install: nie znaleziono polecenia
ovz-install: níor aimsíodh an t-ordú
ovz-install: no se encontró la orden
ovz-install: no s'ha trobat l'ordre
ovz-install: opdracht niet gevonden
ovz-install: parancs nem található
ovz-install: perintah tidak ditemukan
ovz-install: príkaz nenájdený
ovz-install: příkaz nenalezen
ovz-install: команда не найдена
ovz-install: командата не е открита
ovz-install: 命令找不到
ovz-install: コマンドが見つかりません