krdb: 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/krdb - from package: kdebase-workspace

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

On Debian possible default full paths are:

/usr/bin/krdb - from package: kde-workspace-bin

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

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