alsa_in: 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

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/alsa_in - from package: jackd1
/usr/bin/alsa_in - from package: jackd2

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