lxc-clone: 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/lxc-clone - from package: lxc

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

On Debian possible default full paths are:

/usr/bin/lxc-clone - from package: lxc

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

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