mount.ceph: command not found

Have You tried accessing the binary with the full path?

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/mount.ceph - from package: ceph

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

On Debian possible default full paths are:

/sbin/mount.ceph - from package: ceph-fs-common

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