agda: command not found

Have You tried accessing the binary with the full path?

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 Debian possible default full paths are:

/usr/bin/agda - from package: agda-bin

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