refer: 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/refer - from package: groff

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

On Debian possible default full paths are:

/usr/bin/refer - from package: groff

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

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