gnatls: 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/gnatls - from package: gcc-gnat

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

On Debian possible default full paths are:

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

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

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