garmin_gpx: 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/garmin_gpx - from package: garmintools

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/garmin_gpx - from package: garmin-forerunner-tools

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

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