fping6: 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/fping6 - from package: fping

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

On Debian possible default full paths are:

/usr/bin/fping6 - from package: fping

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

Error in other languages:
fping6: bevel nie gevind nie
fping6: comandă negăsită
fping6: comando não encontrado
fping6: commande introuvable
fping6: command not found
fping6: käsku ei ole
fping6: không tìm thấy lệnh
fping6: komanda nerasta
fping6: Kommando nicht gefunden.
fping6: kommandot finns inte
fping6: komut yok
fping6: nie znaleziono polecenia
fping6: níor aimsíodh an t-ordú
fping6: no se encontró la orden
fping6: no s'ha trobat l'ordre
fping6: opdracht niet gevonden
fping6: parancs nem található
fping6: perintah tidak ditemukan
fping6: príkaz nenájdený
fping6: příkaz nenalezen
fping6: команда не найдена
fping6: командата не е открита
fping6: 命令找不到
fping6: コマンドが見つかりません