masscan: 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/bin/masscan - from package: masscan

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

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