lxc-test-concurrent: 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/lxc-test-concurrent - from package: lxc

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

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