pyrexc: 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/pyrexc - from package: Pyrex

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

On Debian possible default full paths are:

/usr/bin/pyrexc - from package: python-pyrex

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

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