fbguard: 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/fbguard - from package: firebird

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

On Debian possible default full paths are:

/usr/sbin/fbguard - from package: firebird2.5-server-common

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

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