gmerlin: 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 Debian possible default full paths are:

/usr/bin/gmerlin - from package: gmerlin

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

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