elk: 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/elk - from package: elk

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

On Debian possible default full paths are:

/usr/bin/elk - from package: elk

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

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