gri: command not found

Have You tried accessing the binary with the full path?

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/gri - from package: gri

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