seren: 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:

/usr/bin/seren - from package: seren

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