midisnoop: 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/midisnoop - from package: midisnoop

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

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