rndc: 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/rndc - from package: bind

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

On Debian possible default full paths are:

/usr/sbin/rndc - from package: bind9utils

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

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