rgrep: 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/rgrep - from package: grep

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

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