ytnef: 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/ytnef - from package: ytnef

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

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