koan: 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/koan - from package: koan

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

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