gdm-binary: 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/sbin/gdm-binary - from package: gdm

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

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