dfgrep: 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 Debian possible default full paths are:

/usr/bin/dfgrep - from package: debian-goodies

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

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