ether-wake: 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

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 CentOS possible default full paths are:

/sbin/ether-wake - from package: net-tools

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