grn: 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/grn - from package: groff

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

On Debian possible default full paths are:

/usr/bin/grn - from package: groff

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

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