luminance-hdr-cli: 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/luminance-hdr-cli - from package: luminance-hdr

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

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