al2: 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/al2 - from package: mono-devel

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

On Debian possible default full paths are:

/usr/bin/al2 - from package: mono-devel

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

Error in other languages:
al2: bevel nie gevind nie
al2: comandă negăsită
al2: comando não encontrado
al2: commande introuvable
al2: command not found
al2: käsku ei ole
al2: không tìm thấy lệnh
al2: komanda nerasta
al2: Kommando nicht gefunden.
al2: kommandot finns inte
al2: komut yok
al2: nie znaleziono polecenia
al2: níor aimsíodh an t-ordú
al2: no se encontró la orden
al2: no s'ha trobat l'ordre
al2: opdracht niet gevonden
al2: parancs nem található
al2: perintah tidak ditemukan
al2: príkaz nenájdený
al2: příkaz nenalezen
al2: команда не найдена
al2: командата не е открита
al2: 命令找不到
al2: コマンドが見つかりません