On 2018-07-06 05:32 -0400, Michael Shell wrote:
> On Fri, 06 Jul 2018 15:44:19 +0800
> Xi Ruoyao <[email protected]> wrote:
>
>
> > There is message from systemd crash handler (showing a SIGABRT and dumping
> > core), but there is no welcome message. So the problem should be in
> > mount_cgroup_controllers.
> >
> > There IS a way to debug systemd - adding log_info into systemd source code
> > to output key variables and debug messages. I was one of the ACM/ICPC
> > contestants who are very familiar with this ``debugging technique". This
> > technique often outperforms GDB in programming contests. :)
>
>
> Xi,
>
> That is really good stuff to know! However, I don't understand what you
> mean by "adding log_info into systemd source code". How exactly do you
> do that? e.g., a debug option the source configure script, a manual
> alteration of source code (and how/where), etc.
log_info() is a systemd internal function. The usage of it is like printf.
It outputs to system log and screen.
For example I can insert
log_info("I am still alive!!!");
into systemd source code somewhere. If I can see the message, I'll know
systemd doesn't crash before the line I inserted. Then I can actually do
a bisect to know which source code line actually crashes.
And I can also output systemd variables like
log_info("foo = %d", foo);
> If it is a cgroup issue, it is required that the kernel be built with:
>
> CONFIG_CGROUPS (it is OK to disable all controllers)
If /proc/cgroups does not exist, there will be an error message
"Failed to enumerate cgroup controllers: No such file or directory"
Systemd seems to handle errors well (most of time). SIGABRT is strange.
Someone said "-D_FORTIY_SOURCE=2" may cause systemd to SIGABRT.
--
Xi Ruoyao <[email protected]>
School of Aerospace Science and Technology, Xidian University
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