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

Question

演示问题的简化例子是

#include <stdio.h>

int main(void)
{
    printf("foo\n");
    fflush(stdout);
    getchar();
    return 0;
}

（尽管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）。

如果编译为运行以下单位：

[Unit]
Description=description
After=network.target

[Service]
ExecStart=/path/to/binary

[Install]
WantedBy=multi-user.target

然后 systemctl restart journald 在大多数情况下不会得到 foo\n 输出，而 syslog 成功地将它写入 /var/log/syslog。

这是服务的 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对应的部分：

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 journald 收到stdout，如果有的话？

Answer 1

tldr，这是一个已知问题。

我在systemd-devel maillist and got a reply with a reference to the reported issue问了同样的问题。