ffwiviewer: 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/ffwiviewer - from package: fawkes-guis

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

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