rdma_xserver: 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/rdma_xserver - from package: librdmacm-utils

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

On Debian possible default full paths are:

/usr/bin/rdma_xserver - from package: rdmacm-utils

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

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