kde4: 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/kde4 - from package: kdebase-runtime

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

On Debian possible default full paths are:

/usr/bin/kde4 - from package: kde-runtime

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

Error in other languages:
kde4: bevel nie gevind nie
kde4: comandă negăsită
kde4: comando não encontrado
kde4: commande introuvable
kde4: command not found
kde4: käsku ei ole
kde4: không tìm thấy lệnh
kde4: komanda nerasta
kde4: Kommando nicht gefunden.
kde4: kommandot finns inte
kde4: komut yok
kde4: nie znaleziono polecenia
kde4: níor aimsíodh an t-ordú
kde4: no se encontró la orden
kde4: no s'ha trobat l'ordre
kde4: opdracht niet gevonden
kde4: parancs nem található
kde4: perintah tidak ditemukan
kde4: príkaz nenájdený
kde4: příkaz nenalezen
kde4: команда не найдена
kde4: командата не е открита
kde4: 命令找不到
kde4: コマンドが見つかりません