grdblend: 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/grdblend - 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/grdblend - from package: GMT

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

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