lvconvert: 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:

/sbin/lvconvert - from package: lvm2

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

On Debian possible default full paths are:

/sbin/lvconvert - from package: lvm2

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

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