ceph-rbdnamer: 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/bin/ceph-rbdnamer - from package: ceph

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

On Debian possible default full paths are:

/usr/bin/ceph-rbdnamer - from package: librbd1

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

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