Re: core sysctl

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Hello Jonny,

On 5/27/20 5:22 PM, Jonny Grant wrote:
> 
> 
> On 27/05/2020 14:32, Michael Kerrisk (man-pages) wrote:
>> Hi Jonny
>>
>> On Wed, 27 May 2020 at 15:23, Jonny Grant <jg@jguk.org> wrote:
>>>
>>>
>>>
>>> On 27/05/2020 14:06, Michael Kerrisk (man-pages) wrote:
>>>> Hi Jonny,
>>>>
>>>> On Mon, 25 May 2020 at 17:08, Jonny Grant <jg@jguk.org> wrote:
>>>>>
>>>>> Suggestion for some additional information on this page:
>>>>>
>>>>> http://man7.org/linux/man-pages/man5/core.5.html
>>>>>
>>>>> Could "Core dumps and systemd" be extended to give an
>>>>> example of sysctl making a temporary change?
>>>>>
>>>>> eg set to the filename and signal that causes the core dump:
>>>>>
>>>>> # sysctl -w kernel.core_pattern="%e-%s.core"
>>>>
>>>> I'm a little confused: what do you mean by "making a *temporary*
>>>> change" (i.e., where does "temporary" come into it)?
>>>>
>>>> Thanks,
>>>>
>>>> Michael
>>>>
>>>
>>> As I understood, this core pattern is set until reboot.
>>
>> Okay, now I understand. Next question: what's the value in having the
>> signal number in the filename?
> 
> The signal number indicates the reason the core was dumped, > eg 11 SIGSEGV,  SIGTRAP is 5.

Sure, it tells us what signal triggered the core dump.
My reason for the question was that it doesn't tell us the
*reason* for the core dump--for example, SIGSEGV can be
generated for many reasons.

> %P %t %I also useful.

Okay. I applied the patch below.

Thanks,

Michael


diff --git a/man5/core.5 b/man5/core.5
index 9725ff64a..6dbaa69b8 100644
--- a/man5/core.5
+++ b/man5/core.5
@@ -533,7 +533,7 @@ For more extensive details, see the
 .BR coredumpctl (1)
 manual page.
 .PP
-To disable the
+To (persistently) disable the
 .BR systemd (1)
 mechanism that archives core dumps, restoring to something more like
 traditional Linux behavior, one can set an override for the
@@ -548,6 +548,18 @@ mechanism, using something like:
 .EE
 .in
 .PP
+It is also possible to temporarily (i.e., until the next reboot) change the
+.I core_patter
+setting using a command such as the following
+(which causes the names of core dump files to include the executable name
+as well as the number of the signal which triggered the core dump):
+.PP
+.in +4n
+.EX
+# \fBsysctl \-w kernel.core_pattern="%e\-%s.core"\fP
+.EE
+.in
+.PP
 .\"
 .SH NOTES
 The


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/