trend2d: 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/trend2d - 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/trend2d - from package: GMT

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

Error in other languages:
trend2d: bevel nie gevind nie
trend2d: comandă negăsită
trend2d: comando não encontrado
trend2d: commande introuvable
trend2d: command not found
trend2d: käsku ei ole
trend2d: không tìm thấy lệnh
trend2d: komanda nerasta
trend2d: Kommando nicht gefunden.
trend2d: kommandot finns inte
trend2d: komut yok
trend2d: nie znaleziono polecenia
trend2d: níor aimsíodh an t-ordú
trend2d: no se encontró la orden
trend2d: no s'ha trobat l'ordre
trend2d: opdracht niet gevonden
trend2d: parancs nem található
trend2d: perintah tidak ditemukan
trend2d: príkaz nenájdený
trend2d: příkaz nenalezen
trend2d: команда не найдена
trend2d: командата не е открита
trend2d: 命令找不到
trend2d: コマンドが見つかりません