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<p class=MsoNormal>Hi All:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I write an event handler to start our daemon service. The
problem is that once the event handler code finished, whole Nagios process keep
hanging. I check the CPU usage is 100% and by using strace I can see a lot of
following system call:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>read(5, 0xbf879450,
1023)
= -1 EAGAIN (Resource temporarily unavailable)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>By checking the source code, I found the reason of this
problem. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Nagios main process create a pipe fd[5,6] and fork a child
process. In this child process, it use popen to create pipe and invoke event
handler script. Once child process get output from event handler script, it transfer
it to main process by using fd 6. Because in popen function, it doesn’t
close fd 6 before invoking event handler script, fd 6 is inherited down to our
daemon process. Because our daemon process doesn’t close fd 6, Nagios
main process keep getting EAGAIN. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Suggestion:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>To fix this problem, I would suggest to fix two parts.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>1 Don’t use popen. Instead create pipe, fork child
process and close all unused file descriptor before invoking event handler script.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>2 In main process, set timeout for getting EAGAIN
error code to avoid endless loop.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Oliver<o:p></o:p></p>
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