Debian systemd通过sigterm终止了我的屏幕会话

/var/log/syslog有以下行：

Mar 13 05:02:34 corben systemd[1]: Stopping User Manager for UID 1000...
Mar 13 05:02:34 corben systemd[1]: Stopped target Graphical Interface.
Mar 13 05:02:34 corben systemd[1]: session-1257696.scope: Killing process 3262 (screen) with signal SIGTERM.
Mar 13 05:02:34 corben systemd[1]: session-1257696.scope: Killing process 3263 (bash) with signal SIGTERM.
Mar 13 05:02:34 corben systemd[1]: session-1257696.scope: Killing process 3390 (bash) with signal SIGTERM.
Mar 13 05:02:34 corben systemd[1]: session-1257696.scope: Killing process 4651 (script) with signal SIGTERM.
Mar 13 05:02:34 corben systemd[1]: session-1257696.scope: Killing process 4652 (bash) with signal SIGTERM.
Mar 13 05:02:34 corben systemd[2558]: Stopped target Default.
Mar 13 05:02:34 corben systemd[2558]: Stopped target Basic System.
Mar 13 05:02:34 corben systemd[2558]: Stopped target Timers.
Mar 13 05:02:34 corben systemd[2558]: Stopped target Paths.
Mar 13 05:02:34 corben systemd[2558]: Stopped target Sockets.
Mar 13 05:02:34 corben systemd[2558]: Closed GnuPG cryptographic agent (ssh-agent emulation).
Mar 13 05:02:34 corben systemd[2558]: Closed GnuPG cryptographic agent and passphrase cache.
Mar 13 05:02:34 corben systemd[2558]: Closed GnuPG cryptographic agent (access for web browsers).
Mar 13 05:02:34 corben systemd[2558]: Closed GnuPG cryptographic agent and passphrase cache (restricted).
Mar 13 05:02:34 corben systemd[2558]: Reached target Shutdown.
Mar 13 05:02:34 corben systemd[2558]: Starting Exit the Session...
Mar 13 05:02:34 corben systemd[1]: session-1257696.scope: Killing process 4694 (bash) with signal SIGTERM.

我与python脚本的屏幕会话被sigterm终止。我想知道这是怎么发生的？请帮忙