grdraster: 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/grdraster - 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/grdraster - from package: GMT

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

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