etherwake: command not found

Have You tried accessing the binary with the full path?

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/etherwake - from package: etherwake

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