lxc-unfreeze: 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-unfreeze - from package: lxc

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

On Debian possible default full paths are:

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

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

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