qemu-system-aarch64: 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 Debian possible default full paths are:

/usr/bin/qemu-system-aarch64 - from package: qemu-system-arm

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

Error in other languages:
qemu-system-aarch64: bevel nie gevind nie
qemu-system-aarch64: comandă negăsită
qemu-system-aarch64: comando não encontrado
qemu-system-aarch64: commande introuvable
qemu-system-aarch64: command not found
qemu-system-aarch64: käsku ei ole
qemu-system-aarch64: không tìm thấy lệnh
qemu-system-aarch64: komanda nerasta
qemu-system-aarch64: Kommando nicht gefunden.
qemu-system-aarch64: kommandot finns inte
qemu-system-aarch64: komut yok
qemu-system-aarch64: nie znaleziono polecenia
qemu-system-aarch64: níor aimsíodh an t-ordú
qemu-system-aarch64: no se encontró la orden
qemu-system-aarch64: no s'ha trobat l'ordre
qemu-system-aarch64: opdracht niet gevonden
qemu-system-aarch64: parancs nem található
qemu-system-aarch64: perintah tidak ditemukan
qemu-system-aarch64: príkaz nenájdený
qemu-system-aarch64: příkaz nenalezen
qemu-system-aarch64: команда не найдена
qemu-system-aarch64: командата не е открита
qemu-system-aarch64: 命令找不到
qemu-system-aarch64: コマンドが見つかりません