gmtdp: 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/gmtdp - from package: GMT

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

On Debian possible default full paths are:

/usr/lib/gmt/bin/gmtdp - from package: GMT

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

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