check-sendfile: 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/check-sendfile - from package: sendfile

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

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