mkcephfs: 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:

/sbin/mkcephfs - from package: ceph

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

On Debian possible default full paths are:

/sbin/mkcephfs - from package: ceph

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

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