wd: 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 CentOS possible default full paths are:

/usr/bin/wd - from package: rubygem-whiskey_disk
/usr/lib/ruby/gems/1.8/gems/whiskey_disk-0.6.24/bin/wd - from package: rubygem-whiskey_disk

You may install the required package with command yum install {package}

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