iotk: 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/iotk - from package: quantum-espresso

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

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