gmtset: 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/gmtset - 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/gmtset - from package: GMT

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

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