mzn-gecode: 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/mzn-gecode - from package: gecode-devel

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

On Debian possible default full paths are:

/usr/bin/mzn-gecode - from package: flatzinc

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

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