port-helper: 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/port-helper - from package: uml_utilities

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

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