grdtrack: 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/grdtrack - 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/grdtrack - from package: GMT

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

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