traffic_server: 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_server - from package: trafficserver

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

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