qbittorrent: 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/qbittorrent - from package: qbittorrent

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

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