virt-install: 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-install - from package: python-virtinst
/usr/sbin/virt-install - from package: python-virtinst

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

On Debian possible default full paths are:

/usr/bin/virt-install - from package: virtinst

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

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