strace -f not following child process

Denys Vlasenko dvlasenk at
Mon Jul 8 08:00:10 UTC 2013

On 07/05/2013 01:18 PM, Florian Kelbert wrote:
> Hi all,
> while trying to strace nginx (, using strace -f, I 
> realized that strace fails to trace a forked child process.

Which version of strace and kernel do you have?

Can you show the same event with -d option added to strace
command line? (the debug output goes to stderr, not -o LOGFILE).

> As you can see in the trace below, process 13644 forks a new child 
> 13645. 13644 and 13643 then exit and the new process 13645 does not get 
> traced. As far as I have understood the strace source code, the reason 
> may be that all parent processes exit before 16345 has executed any 
> single system call.

May be, but it is unlikely, seeing your trace. 13643 did quite a number
of syscalls after clone.

> Am I doing something wrong?

Hard to say, as you didn't show your strace command line.

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