xzfgrep: 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/xzfgrep - from package: xz

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

On Debian possible default full paths are:

/usr/bin/xzfgrep - from package: xz-utils

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

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