rarpwatch: 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/rarpwatch - from package: argus-client

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

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