selinuxdefcon: 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/sbin/selinuxdefcon - from package: libselinux-utils

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