virt-v2v: command not found

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/virt-v2v - from package: virt-v2v

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/virt-v2v - from package: libguestfs-tools

You may install the required package with command apt-get install {package}

Error in other languages:
virt-v2v: bevel nie gevind nie
virt-v2v: comandă negăsită
virt-v2v: comando não encontrado
virt-v2v: commande introuvable
virt-v2v: command not found
virt-v2v: käsku ei ole
virt-v2v: không tìm thấy lệnh
virt-v2v: komanda nerasta
virt-v2v: Kommando nicht gefunden.
virt-v2v: kommandot finns inte
virt-v2v: komut yok
virt-v2v: nie znaleziono polecenia
virt-v2v: níor aimsíodh an t-ordú
virt-v2v: no se encontró la orden
virt-v2v: no s'ha trobat l'ordre
virt-v2v: opdracht niet gevonden
virt-v2v: parancs nem található
virt-v2v: perintah tidak ditemukan
virt-v2v: príkaz nenájdený
virt-v2v: příkaz nenalezen
virt-v2v: команда не найдена
virt-v2v: командата не е открита
virt-v2v: 命令找不到
virt-v2v: コマンドが見つかりません