sems: 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/sbin/sems - from package: sems

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

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