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Re: [nmh-workers] strace show # pauses/takes 5+ sec | network issue? ( not nmh )

2019-09-08 20:11:15
Hi Ken:

On Sun 9/8/19 18:09 -0400 Ken Hornstein wrote:
So what should I be asking my vps provider?  Is this some network issue?

Almost certainly "yes".  If I had to guess I would think it was a DNS
timeout on something somewhere.

I thought it might be dns. Earlier in the day, twice in a row it hung near the 
end of
this snip:

connect(4, {sa_family=AF_INET, sin_port=htons(53), 
sin_addr=inet_addr("")}, 16) = 0
clock_gettime(CLOCK_REALTIME, {tv_sec=1567958940, tv_nsec=908626657}) = 0
poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
sendmmsg(4, [{msg_hdr={msg_name=NULL, msg_namelen=0, 
iov_len=32}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, msg_len=32}, 
{msg_hdr={msg_name=NULL, msg_namelen=0, 
iov_len=32}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, msg_len=32}], 2, 

where ibisbil.mumble.com is the obfuscated hostname of the fedora vps with the 
problem, and
is the 1st nameserver in ibisbil.mumble.com:/etc/resolv.conf. Later in the day 
though the strace stalled
consistently at the spot shown in my first post.

But unfortunately these system call traces are not very helpful.  This
is because you are tracing the command "command", and all that shows is
you execute a nmh command and it waits 5 seconds for it to complete.

OK/thanks. In the future I will plan to run for example:

    strace -o /tmp/foo -t -f /usr/local/nmh/bin/scan last

If this happens in the future you should probably use the -f option to
trace all children of the specified process/command, and the -t option
to print the system call timestamps (that would let you see exactly
where the delay is).  I also like using -o to direct the trace output to
a file rather than having it mixed in with the output of a process.

Appreciate learning about the -t, -f,  and -o switches!



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