virsh: 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/virsh - from package: libvirt-client

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

On Debian possible default full paths are:

/usr/bin/virsh - from package: libvirt-clients

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

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