usernetctl: 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/sbin/usernetctl - from package: initscripts

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

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