asunder: 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/asunder - from package: asunder

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