walldns: 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/walldns - from package: ndjbdns

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

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