kstartupconfig: 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/kstartupconfig - from package: kdelibs3

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

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