nsenter: 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/nsenter - from package: util-linux-ng

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

On Debian possible default full paths are:

/usr/bin/nsenter - from package: util-linux

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

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