aa-notify: 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/aa-notify - from package: apparmor-notify

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

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