emu8051-gtk: 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/emu8051-gtk - from package: emu8051

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

Error in other languages:
emu8051-gtk: bevel nie gevind nie
emu8051-gtk: comandă negăsită
emu8051-gtk: comando não encontrado
emu8051-gtk: commande introuvable
emu8051-gtk: command not found
emu8051-gtk: käsku ei ole
emu8051-gtk: không tìm thấy lệnh
emu8051-gtk: komanda nerasta
emu8051-gtk: Kommando nicht gefunden.
emu8051-gtk: kommandot finns inte
emu8051-gtk: komut yok
emu8051-gtk: nie znaleziono polecenia
emu8051-gtk: níor aimsíodh an t-ordú
emu8051-gtk: no se encontró la orden
emu8051-gtk: no s'ha trobat l'ordre
emu8051-gtk: opdracht niet gevonden
emu8051-gtk: parancs nem található
emu8051-gtk: perintah tidak ditemukan
emu8051-gtk: príkaz nenájdený
emu8051-gtk: příkaz nenalezen
emu8051-gtk: команда не найдена
emu8051-gtk: командата не е открита
emu8051-gtk: 命令找不到
emu8051-gtk: コマンドが見つかりません