gnatmake: 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/gnatmake - from package: gcc-gnat

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

On Debian possible default full paths are:

/usr/bin/gnatmake - from package: gnat-4.9

You may install the required package with command apt-get install {package}

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