grok: 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/grok - from package: grok

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