k3b: 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/k3b - from package: k3b

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

On Debian possible default full paths are:

/usr/bin/k3b - from package: k3b

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

Error in other languages:
k3b: bevel nie gevind nie
k3b: comandă negăsită
k3b: comando não encontrado
k3b: commande introuvable
k3b: command not found
k3b: käsku ei ole
k3b: không tìm thấy lệnh
k3b: komanda nerasta
k3b: Kommando nicht gefunden.
k3b: kommandot finns inte
k3b: komut yok
k3b: nie znaleziono polecenia
k3b: níor aimsíodh an t-ordú
k3b: no se encontró la orden
k3b: no s'ha trobat l'ordre
k3b: opdracht niet gevonden
k3b: parancs nem található
k3b: perintah tidak ditemukan
k3b: príkaz nenájdený
k3b: příkaz nenalezen
k3b: команда не найдена
k3b: командата не е открита
k3b: 命令找不到
k3b: コマンドが見つかりません