irunner: 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/irunner - from package: python-ipython-console

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

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