iscsi_discovery: 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 Debian possible default full paths are:

/usr/sbin/iscsi_discovery - from package: open-iscsi

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

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