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/sbin/sparsify - from package: zerofree

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

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