virt-sparsify: 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/virt-sparsify - from package: libguestfs-tools-c

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

On Debian possible default full paths are:

/usr/bin/virt-sparsify - from package: libguestfs-tools

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

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