lxc-unshare: 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-unshare - from package: lxc

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

On Debian possible default full paths are:

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

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

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