mgd77header: 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/mgd77header - 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/mgd77header - from package: GMT

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

Error in other languages:
mgd77header: bevel nie gevind nie
mgd77header: comandă negăsită
mgd77header: comando não encontrado
mgd77header: commande introuvable
mgd77header: command not found
mgd77header: käsku ei ole
mgd77header: không tìm thấy lệnh
mgd77header: komanda nerasta
mgd77header: Kommando nicht gefunden.
mgd77header: kommandot finns inte
mgd77header: komut yok
mgd77header: nie znaleziono polecenia
mgd77header: níor aimsíodh an t-ordú
mgd77header: no se encontró la orden
mgd77header: no s'ha trobat l'ordre
mgd77header: opdracht niet gevonden
mgd77header: parancs nem található
mgd77header: perintah tidak ditemukan
mgd77header: príkaz nenájdený
mgd77header: příkaz nenalezen
mgd77header: команда не найдена
mgd77header: командата не е открита
mgd77header: 命令找不到
mgd77header: コマンドが見つかりません