grd2cpt: 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/grd2cpt - 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/grd2cpt - from package: GMT

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

Error in other languages:
grd2cpt: bevel nie gevind nie
grd2cpt: comandă negăsită
grd2cpt: comando não encontrado
grd2cpt: commande introuvable
grd2cpt: command not found
grd2cpt: käsku ei ole
grd2cpt: không tìm thấy lệnh
grd2cpt: komanda nerasta
grd2cpt: Kommando nicht gefunden.
grd2cpt: kommandot finns inte
grd2cpt: komut yok
grd2cpt: nie znaleziono polecenia
grd2cpt: níor aimsíodh an t-ordú
grd2cpt: no se encontró la orden
grd2cpt: no s'ha trobat l'ordre
grd2cpt: opdracht niet gevonden
grd2cpt: parancs nem található
grd2cpt: perintah tidak ditemukan
grd2cpt: príkaz nenájdený
grd2cpt: příkaz nenalezen
grd2cpt: команда не найдена
grd2cpt: командата не е открита
grd2cpt: 命令找不到
grd2cpt: コマンドが見つかりません