mkzonedb: 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/sbin/mkzonedb - from package: isdn4k-utils

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

On Debian possible default full paths are:

/usr/sbin/mkzonedb - from package: isdnlog

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

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