semodule_expand: 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/semodule_expand - from package: policycoreutils

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

On Debian possible default full paths are:

/usr/bin/semodule_expand - from package: policycoreutils

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

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