system3: 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/system3 - from package: simh

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

Error in other languages:
system3: bevel nie gevind nie
system3: comandă negăsită
system3: comando não encontrado
system3: commande introuvable
system3: command not found
system3: käsku ei ole
system3: không tìm thấy lệnh
system3: komanda nerasta
system3: Kommando nicht gefunden.
system3: kommandot finns inte
system3: komut yok
system3: nie znaleziono polecenia
system3: níor aimsíodh an t-ordú
system3: no se encontró la orden
system3: no s'ha trobat l'ordre
system3: opdracht niet gevonden
system3: parancs nem található
system3: perintah tidak ditemukan
system3: príkaz nenájdený
system3: příkaz nenalezen
system3: команда не найдена
system3: командата не е открита
system3: 命令找不到
system3: コマンドが見つかりません