如何保证程序退出时刷新 systemd 和 journald 之间的标准输出缓冲区?

Question

演示问题的简化示例是

#include <stdio.h>
int main(void)
{
printf("foon");
fflush(stdout);
getchar();
return 0;
}

(虽然它不是特定于编程语言的 - 我发现问题的原始应用程序是在 Go 中(。

如果它已编译并由以下单元运行：

[Unit]
Description=description
After=network.target
[Service]
ExecStart=/path/to/binary
[Install]
WantedBy=multi-user.target

然后systemctl restartjournald在大多数情况下不会得到foon输出，而syslog成功地将其写到/var/log/syslog。

下面是服务的journald输出示例：

May 18 08:30:38 hostname systemd[1]: Stopped servicename
May 18 08:30:38 hostname systemd[1]: Started servicename
May 18 08:30:38 hostname systemd[1]: Stopped servicename
May 18 08:30:38 hostname systemd[1]: Started servicename
May 18 08:30:38 hostname servicename[7701]: foo
May 18 08:30:41 hostname systemd[1]: Stopped servicename
May 18 08:30:41 hostname systemd[1]: Started servicename
May 18 08:30:46 hostname systemd[1]: Stopped servicename
May 18 08:30:46 hostname systemd[1]: Started servicename

然后是/var/log/syslog的相应部分：

May 18 08:30:38 hostname systemd[1]: Stopped servicename.
May 18 08:30:38 hostname systemd[1]: Started servicename.
May 18 08:30:38 hostname servicename[7682]: foo
May 18 08:30:38 hostname systemd[1]: Stopped servicename.
May 18 08:30:38 hostname systemd[1]: Started servicename.
May 18 08:30:38 hostname servicename[7701]: foo
May 18 08:30:41 hostname systemd[1]: Stopped servicename.
May 18 08:30:41 hostname systemd[1]: Started servicename.
May 18 08:30:41 hostname servicename[7720]: foo
May 18 08:30:46 hostname systemd[1]: Stopped servicename.
May 18 08:30:46 hostname systemd[1]: Started servicename.
May 18 08:30:46 hostname servicename[7739]: foo

有什么方法可以保证日记收到stdout，如果有的话？

Answer 1

TLDR，这是一个已知问题。

我在systemd-devel邮件列表中问了同样的问题，并得到了有关报告问题的回复。