gnatkr: 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/gnatkr - from package: gcc-gnat

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

On Debian possible default full paths are:

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

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

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