Issue #6726 has been updated by nobu (Nobuyoshi Nakada).


I think the following document introduced at #4149 is wrong, since errno is C-level interface and not available in Ruby-level, and may not be preserved across method calls.

  %m is replaced with the error message string that would be returned by strerror(errno).

So possible fixes would be:
(1) fix document, by removing above sentence.
(2) replace %m with other thing, $! for example.

The latter sounds useful, but will be larger change.

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Bug #6726: Syslog crashes when the special %m tag (of syslog(3)) is present in the message
https://bugs.ruby-lang.org/issues/6726#change-27986

Author: ameuret (Arnaud MEURET)
Status: Open
Priority: Low
Assignee: 
Category: 
Target version: 
ruby -v: ruby 1.9.2p180 (2011-02-18 revision 30909) [i686-linux] 


The %m special escape sequence supported by the syslog(3) system call is claimed by the Ruby doc to be supported by the ::Syslog Ruby class. However the implementation of ::Syslog in ext/syslog/syslog.c:49 (https://github.com/ruby/ruby/blob/trunk/ext/syslog/syslog.c#L49) calls rb_f_sprintf() which does not tolerate the presence of %m in the format string.

A quick dump of a pry session demonstrating the crash:

[1] pry(main)> require 'syslog'
=> true
[2] pry(main)> Syslog.open
=> <#Syslog: opened=true, ident="pry", options=3, facility=8, mask=255>
[3] pry(main)> ::Syslog.info "Hi !%m"
ArgumentError: malformed format string - %m
from (pry):3:in `info 



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