disk_traffic: 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/disk_traffic - from package: libstatgrab-examples

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

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