xfs_estimate: 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/xfs_estimate - from package: xfsprogs

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

On Debian possible default full paths are:

/usr/sbin/xfs_estimate - from package: xfsprogs

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

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