hostbyname: 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/hostbyname - from package: squidGuard

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

On Debian possible default full paths are:

/usr/bin/hostbyname - from package: squidGuard

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

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