gmtconvert: 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/gmtconvert - 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/gmtconvert - from package: GMT

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

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