为什么“systemd[1]：user@65534.service：杀死进程”

Question

我最近升级到 Debian 9 的某些服务器现在每天都会产生一条奇怪的 syslog 消息（通过 logcheck 报告）：

Oct 27 06:25:08 foo systemd[1]: user@65534.service: Killing process 12270 (kill) with signal SIGKILL.

时间似乎是 cron.daily 的时间，服务的名称看起来像 nobody/nogroup 的 UID，但是为什么它会死掉，它首先在做什么？

那个时候有更多的系统日志行。该块重复了几次：

Oct 27 06:25:08 svn systemd[1]: Created slice User Slice of nobody.
Oct 27 06:25:08 svn systemd[1]: Starting User Manager for UID 65534...
Oct 27 06:25:08 svn systemd[1]: Started Session 1377 of user nobody.
Oct 27 06:25:08 svn systemd[12264]: Reached target Paths.
Oct 27 06:25:08 svn systemd[12264]: Listening on GnuPG cryptographic agent (access for web browsers).
Oct 27 06:25:08 svn systemd[12264]: Listening on GnuPG network certificate management daemon.
Oct 27 06:25:08 svn systemd[12264]: Reached target Timers.
Oct 27 06:25:08 svn systemd[12264]: Listening on GnuPG cryptographic agent and passphrase cache (restricted).
Oct 27 06:25:08 svn systemd[12264]: Listening on GnuPG cryptographic agent (ssh-agent emulation).
Oct 27 06:25:08 svn systemd[12264]: Listening on GnuPG cryptographic agent and passphrase cache.
Oct 27 06:25:08 svn systemd[12264]: Reached target Sockets.
Oct 27 06:25:08 svn systemd[12264]: Reached target Basic System.
Oct 27 06:25:08 svn systemd[12264]: Reached target Default.
Oct 27 06:25:08 svn systemd[12264]: Startup finished in 12ms.
Oct 27 06:25:08 svn systemd[1]: Started User Manager for UID 65534.
Oct 27 06:25:08 svn systemd[1]: Stopping User Manager for UID 65534...
Oct 27 06:25:08 svn systemd[12264]: Stopped target Default.
Oct 27 06:25:08 svn systemd[12264]: Stopped target Basic System.
Oct 27 06:25:08 svn systemd[12264]: Stopped target Sockets.
Oct 27 06:25:08 svn systemd[12264]: Closed GnuPG cryptographic agent and passphrase cache.
Oct 27 06:25:08 svn systemd[12264]: Closed GnuPG network certificate management daemon.
Oct 27 06:25:08 svn systemd[12264]: Closed GnuPG cryptographic agent (access for web browsers).
Oct 27 06:25:08 svn systemd[12264]: Closed GnuPG cryptographic agent and passphrase cache (restricted).
Oct 27 06:25:08 svn systemd[12264]: Closed GnuPG cryptographic agent (ssh-agent emulation).
Oct 27 06:25:08 svn systemd[12264]: Reached target Shutdown.
Oct 27 06:25:08 svn systemd[12264]: Starting Exit the Session...
Oct 27 06:25:08 svn systemd[12264]: Stopped target Timers.
Oct 27 06:25:08 svn systemd[12264]: Stopped target Paths.
Oct 27 06:25:08 svn systemd[12264]: Received SIGRTMIN+24 from PID 12270 (kill).
Oct 27 06:25:08 svn systemd[1]: user@65534.service: Killing process 12270 (kill) with signal SIGKILL.
Oct 27 06:25:08 svn systemd[1]: Stopped User Manager for UID 65534.
Oct 27 06:25:08 svn systemd[1]: Removed slice User Slice of nobody.
Oct 27 06:25:08 svn systemd[1]: Created slice User Slice of nobody.

PID 12264 在 syslog/syslog.1 中没有其他条目。