v4lctl: 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/v4lctl - from package: xawtv

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

On Debian possible default full paths are:

/usr/bin/v4lctl - from package: xawtv

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

Error in other languages:
v4lctl: bevel nie gevind nie
v4lctl: comandă negăsită
v4lctl: comando não encontrado
v4lctl: commande introuvable
v4lctl: command not found
v4lctl: käsku ei ole
v4lctl: không tìm thấy lệnh
v4lctl: komanda nerasta
v4lctl: Kommando nicht gefunden.
v4lctl: kommandot finns inte
v4lctl: komut yok
v4lctl: nie znaleziono polecenia
v4lctl: níor aimsíodh an t-ordú
v4lctl: no se encontró la orden
v4lctl: no s'ha trobat l'ordre
v4lctl: opdracht niet gevonden
v4lctl: parancs nem található
v4lctl: perintah tidak ditemukan
v4lctl: príkaz nenájdený
v4lctl: příkaz nenalezen
v4lctl: команда не найдена
v4lctl: командата не е открита
v4lctl: 命令找不到
v4lctl: コマンドが見つかりません