gresistor: 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/gresistor - from package: gresistor

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

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