Re: core man page %e

[Jonny Grant <jg@jguk.org>]

On 09/06/2020 11:18, Michael Kerrisk (man-pages) wrote:
> Hello Jonny,
> 
> On 5/30/20 12:39 PM, Jonny Grant wrote:
>> Hello mtk
>>
>> I've noticed "%e-%s.core" often gives something other than the
>> filename and the name is truncated to 16 bytes:-
>>
>> ThreadPoolServi-5.core
>> Chrome_InProcUt-5.core
>>
>> This was set:
>> sysctl -w kernel.core_pattern="%e-%s.core"
>>
>>
>>
>> In multithreaded applications it looks like %e is giving something
>> other than the filename, perhaps a thread entry-point symbol name.>
>> https://www.man7.org/linux/man-pages/man5/core.5.html
>>
>>              %e  executable filename (without path prefix)
>>
>> Could this be updated to:
>>
>>              %e  executable filename or thread name truncated to 16 bytes
> 
> I changed it to this:
> 
>             %e  The process or thread's comm value, which typically is the
>                 same  as the executable filename (without path prefix, and
>                 truncated to a maximum of 15  characters),  but  may  have
>                 been  modified  to be something different; see the discus‐
>                 sion of /proc/[pid]/comm  and  /proc/[pid]/task/[tid]/comm
>                 in proc(5).

Hi Michael

That looks good.

I saw $ top -H shows these similar 15 byte truncated names. It's a shame it is such a low limit.

19697 jonny     20   0  657252  46120  29096 S  2.6  0.3   0:18.84 gnome-terminal- 
 
 

19431 jonny     20   0 4823508 114384  75668 S  1.6  0.7   0:00.08 ThreadPoolForeg


Is it better to say "15 bytes" because utf8 binary filenames or thread names would be less characters?

For example:

$ ./おはようございます
$ cat /proc/892/comm
おはようご

That is 15 bytes of utf8
E3 81 8A E3 81 AF E3 82 88 E3 81 86 E3 81 94 0A

Cheers, Jonny