kstart: 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/kstart - from package: kdebase-runtime

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

On Debian possible default full paths are:

/usr/bin/kstart - from package: kde-runtime

You may install the required package with command apt-get install {package}

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