v4l2ctrl: 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/v4l2ctrl - from package: v4l2ucp

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

Error in other languages:
v4l2ctrl: bevel nie gevind nie
v4l2ctrl: comandă negăsită
v4l2ctrl: comando não encontrado
v4l2ctrl: commande introuvable
v4l2ctrl: command not found
v4l2ctrl: käsku ei ole
v4l2ctrl: không tìm thấy lệnh
v4l2ctrl: komanda nerasta
v4l2ctrl: Kommando nicht gefunden.
v4l2ctrl: kommandot finns inte
v4l2ctrl: komut yok
v4l2ctrl: nie znaleziono polecenia
v4l2ctrl: níor aimsíodh an t-ordú
v4l2ctrl: no se encontró la orden
v4l2ctrl: no s'ha trobat l'ordre
v4l2ctrl: opdracht niet gevonden
v4l2ctrl: parancs nem található
v4l2ctrl: perintah tidak ditemukan
v4l2ctrl: príkaz nenájdený
v4l2ctrl: příkaz nenalezen
v4l2ctrl: команда не найдена
v4l2ctrl: командата не е открита
v4l2ctrl: 命令找不到
v4l2ctrl: コマンドが見つかりません