detect_sniffer6: 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/detect_sniffer6 - from package: thc-ipv6

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

Error in other languages:
detect_sniffer6: bevel nie gevind nie
detect_sniffer6: comandă negăsită
detect_sniffer6: comando não encontrado
detect_sniffer6: commande introuvable
detect_sniffer6: command not found
detect_sniffer6: käsku ei ole
detect_sniffer6: không tìm thấy lệnh
detect_sniffer6: komanda nerasta
detect_sniffer6: Kommando nicht gefunden.
detect_sniffer6: kommandot finns inte
detect_sniffer6: komut yok
detect_sniffer6: nie znaleziono polecenia
detect_sniffer6: níor aimsíodh an t-ordú
detect_sniffer6: no se encontró la orden
detect_sniffer6: no s'ha trobat l'ordre
detect_sniffer6: opdracht niet gevonden
detect_sniffer6: parancs nem található
detect_sniffer6: perintah tidak ditemukan
detect_sniffer6: príkaz nenájdený
detect_sniffer6: příkaz nenalezen
detect_sniffer6: команда не найдена
detect_sniffer6: командата не е открита
detect_sniffer6: 命令找不到
detect_sniffer6: コマンドが見つかりません