vgreduce: 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/vgreduce - from package: lvm2

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

On Debian possible default full paths are:

/sbin/vgreduce - from package: lvm2

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

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