network_iface_stats: 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/network_iface_stats - from package: libstatgrab-examples

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

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