ceph-rest-api: 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-rest-api - from package: ceph

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

On Debian possible default full paths are:

/usr/bin/ceph-rest-api - from package: ceph-common

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

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