gmessage: 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/gmessage - from package: gxmessage

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

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