dftest: 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/dftest - from package: wireshark

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

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