ceph-disk-activate: 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/ceph-disk-activate - from package: ceph

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

On Debian possible default full paths are:

/usr/sbin/ceph-disk-activate - from package: ceph

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

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