pdns_recursor: 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/pdns_recursor - from package: pdns-recursor

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

On Debian possible default full paths are:

/usr/sbin/pdns_recursor - from package: pdns-recursor

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

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