iok: 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/iok - from package: iok

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

On Debian possible default full paths are:

/usr/bin/iok - from package: iok

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

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