fex: 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/fex - from package: fex

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

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