gwhy-bin: 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/gwhy-bin - from package: why

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

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