aha: 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/aha - from package: aha

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

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