traffic_ctl: 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/traffic_ctl - from package: trafficserver

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

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