grd2xyz: 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/grd2xyz - 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/grd2xyz - from package: GMT

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

Error in other languages:
grd2xyz: bevel nie gevind nie
grd2xyz: comandă negăsită
grd2xyz: comando não encontrado
grd2xyz: commande introuvable
grd2xyz: command not found
grd2xyz: käsku ei ole
grd2xyz: không tìm thấy lệnh
grd2xyz: komanda nerasta
grd2xyz: Kommando nicht gefunden.
grd2xyz: kommandot finns inte
grd2xyz: komut yok
grd2xyz: nie znaleziono polecenia
grd2xyz: níor aimsíodh an t-ordú
grd2xyz: no se encontró la orden
grd2xyz: no s'ha trobat l'ordre
grd2xyz: opdracht niet gevonden
grd2xyz: parancs nem található
grd2xyz: perintah tidak ditemukan
grd2xyz: príkaz nenájdený
grd2xyz: příkaz nenalezen
grd2xyz: команда не найдена
grd2xyz: командата не е открита
grd2xyz: 命令找不到
grd2xyz: コマンドが見つかりません