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Top Forums UNIX for Advanced & Expert Users when a process fails to write to /dev/log Post 302436540 by malcolmpdx on Monday 12th of July 2010 09:52:11 AM
Old 07-12-2010
Assuming you mean "when does a process fail to write to /dev/log?"

/dev/log is a semi-standard convention for syslog - syslog listens on this UNIX socket, and writes what is written there according to the rules in it's configuration file.

Given that, you've got three reasons why a process might not be able to log:
  1. The process in question isn't set up to do syslog. Using syslog is optional, and needs to be part of the process code.
  2. syslogd isn't running, so there's nothing reading from that socket.
  3. There is a syslogd running, and the process is set up to log to syslog, but it fails before it reaches the part of it's code when it does.

To check for the first, if you have the source code for the process, check it for calls to openlog(), syslog(), and closelog(), or if it's a shell script, check for calls to the logger program. Perl scripts will usually use Sys::Syslog or something similar.

To check for the second, do:
Code:
 $ ps -efawww | egrep syslog

or even better

Code:
 # lsof /dev/log

and see what has /dev/log open

To check for the third, well, you might try running the process under a debugger, and see if you can catch any writes to /dev/log or calls to syslog. Or, you could run the process via "strace" (truss on some Unixes) and look for writes that way.
 

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Log::Dispatch::Syslog(3)				User Contributed Perl Documentation				  Log::Dispatch::Syslog(3)

NAME
Log::Dispatch::Syslog - Object for logging to system log. SYNOPSIS
use Log::Dispatch; my $log = Log::Dispatch->new ( outputs => [ [ 'Syslog', min_level => 'info', ident => 'Yadda yadda' ] ] ); $log->emerg( "Time to die." ); DESCRIPTION
This module provides a simple object for sending messages to the system log (via UNIX syslog calls). Note that logging may fail if you try to pass UTF-8 characters in the log message. If logging fails and warnings are enabled, the error message will be output using Perl's "warn". CONSTRUCTOR
The constructor takes the following parameters in addition to the standard parameters documented in Log::Dispatch::Output: o ident ($) This string will be prepended to all messages in the system log. Defaults to $0. o logopt ($) A string containing the log options (separated by any separator you like). See the openlog(3) and Sys::Syslog docs for more details. Defaults to ''. o facility ($) Specifies what type of program is doing the logging to the system log. Valid options are 'auth', 'authpriv', 'cron', 'daemon', 'kern', 'local0' through 'local7', 'mail, 'news', 'syslog', 'user', 'uucp'. Defaults to 'user' o socket ($) Tells what type of socket to use for sending syslog messages. Valid options are listed in "Sys::Syslog". If you don't provide this, then we let "Sys::Syslog" simply pick one that works, which is the preferred option, as it makes your code more portable. AUTHOR
Dave Rolsky, <autarch@urth.org> perl v5.12.1 2009-09-22 Log::Dispatch::Syslog(3)
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