xmtr: 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/xmtr - from package: mtr-gtk

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

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