ttysnoops: 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/sbin/ttysnoops - from package: ttysnoop

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

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