Spying on Apache and PHP with Strace

This video shows how to use strace to determine why an apache worker loads a page slowly. Commands shown in this video:

telnet localhost 80
lsof -p `pidof telnet`
netstat -nap | grep pid
strace -o /tmp/output -f -s4096 -r -p pid
cat /tmp/output | cut -c12-16 | sort -rn | head

Category:

Science & Technology

Tags:

• linux
• apache
• php
• strace

[brusdaar]

at 13:47 how did you suddenly get from that php code to the read/write result? How would you know which result too look for once you found the php line?

[elspuddo]

@brusdaar This is a big 4k string of text, and the beginning of the line didn't show up on the screen at 13:47. A little later at 14:00 I move up a bit and you can see the beginning of that line (one line down from the cursor) which begins with "read(11,\1...." . At 14:00 can you see the read, but not the smoking gun (the embedded PHP sleep) although it is there. The PHP code came from a mysql write/read (query/response) action, but it wasn't clear because you couldn't see the whole line.

[iamfaze]

Did you bump up the Apache timeouts? IIRC you dont typically get that long to look for it.

[elspuddo]

@iamfaze I didn't mess with the apache timeouts, I think they were default for CentOS. You're right though, it seems the timeouts are often much tighter than that.

[pu3he]

Great and informative video, many thanks for your effort!

[bflance]

Simply awesome video!

I wonder if its possible to use STRACE to see if a process is trying to delete files/folders...

[agliddenjunk]

What flavor is that? Looks like an awesome setup.

[statikeffeck]

very thorough and "extreme" web debugging. Might come in handy one day.

[rhohan]

video is very informative. please turn your volume up though :)

[theillien]

I'll have to apply this to Apache and Perl now. Good job on the video and thanks.