sys-unconfig: 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/sbin/sys-unconfig - from package: initscripts

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

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