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The Magic of strace

chadfowler.com

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Re: The Magic of strace

#51

Post by 72deluxe »

jrockway wrote: post #10
CrispEditor wrote: post #6

Please see ftp://86.0.252.89/pub/release/website/tools/trace-20140126-x86_64-b95.tar.gz This is a tool called ptrace - which does everything that strace does and a lot more. You have working binaries in there, and most of the source - I havent extricated the full build dependencies so it all builds, but this includes extra facilities like reporting summaries of process trees, showing only connections or files, and sh…

I am a bit paranoid about downloading a binary from a site without a domain name.

Since IP address ranges are allocated in blocks to ISPs, you can do an IP lookup and discover that this fellow is in the UK using a Virgin Cable connection.

So now we know his ISP too. Useful, eh?

Re: The Magic of strace

#53

Post by danielweber »

rosser wrote: post #4

Small, somewhat nit-picky critique: the man pages for system calls are in section 2. If you want to see the docs for the "read()" syscall, and not the bash builtin "read", saying "man read" w̶o̶n̶'̶t̶ may not (see follow-up) do what you expect. Instead, you should say man 2 read This should probably be mentioned somewhere. Otherwise, great writeup. Thanks for sharing! (edited)

Different Unix systems take different syntax for specifying the section. Long ago I learned to say "man -a read" and just get _all_ the "read" pages, scanning for the ones I want (and sometimes learning about things I didn't know were there).

Re: The Magic of strace

#54

Post by JasuM »

JoshTriplett wrote: post #11
rosser wrote: post #4

Small, somewhat nit-picky critique: the man pages for system calls are in section 2. If you want to see the docs for the "read()" syscall, and not the bash builtin "read", saying "man read" w̶o̶n̶'̶t̶ may not (see follow-up) do what you expect. Instead, you should say man 2 read This should probably be mentioned somewhere. Otherwise, great writeup. Thanks for sharing! (edited)

There's a manpage bash-builtins in section 7, but I've never seen a system that had manpages for the individual builtins, let alone having them in section 1. "man read" on every system I've used opens the read manpage in section 2.

At least on my Mac, it opens the page for BUILTIN(1).

Re: The Magic of strace

#55

Post by dalorin »

mrfusion wrote: post #50

Has anyone heard of a program that will take strace (or dtrace) output and create a pretty diagram showing which commands call which commands and which files they read or create? We've got a fairly complicated bioinformatics pipeline that calls about 100 other programs, and creates or reads about 100 different files. I'd love a way to create a picture of what's going on. Which files each program uses, etc. If such a…

Valgrind's callgrind tool will profile all calls a program makes. You can them feed the output to kcachegrind (or qcachegrind for the Qt version) which will nicely visualize the profiling run.

Re: The Magic of strace

#56

Post by edwintorok »

gopalv wrote: post #25

"perf top -e syscalls: statfs " particularly when you don't know which process is calling all the syscalls. Mix "perf record" and "perf trace" & you have the next generation of strace tools.

So they integrated that upstream, I always wondered what happened to the tool announced here: http://lwn.net/Articles/415728/

  perf --help
    trace           strace inspired tool

Re: The Magic of strace

#57

Post by glazskunrukitis »

darklajid wrote: post #39
glazskunrukitis wrote: post #17

Earlier quoted context omitted.

Why do you link directly to the download file? A link to the tool's man page[1] would be sufficient. [1] http://linux.die.net/man/2/ptrace

I might be wrong, but I'm reasonably sure that you link to the system call's man page. Which is probably what the tool in question uses, but .. not the same thing. Elsewhere in this discussion: There's a difference between man page section 1 and 2 - and read was quoted as an example for a potential ambiguous result if you invoke "man read" (opens man 1 read here, when man 2 read was the syscall I might want to look a…

Yes, you are probably right, but the direct link to .tar.gz was not reasonable.

Re: The Magic of strace

#58

Post by dmpk2k »

hobo_mark wrote: post #33
_kp6z wrote: post #20

If you think strace is useful, wait until you try dtrace.

while we wait, could you elaborate on that? ;)

strace shows syscalls -- it's effectively truss.

That's useful and all, but what if you want to instrument arbitrary parts of a program, not just the syscall interface? By function or instruction? Either in userspace or in kernel? With statistical functions? And speculative tracing? And extensive control flow (except loops, which prevent certain safely guarantees DTrace makes). And a lot more.

Don't be fooled by the single-letter change: strace is to DTrace what edlin is to emacs. Or something else ridiculously extreme. They're barely comparable.

Re: The Magic of strace

#60

Post by wglb »

rosser wrote: post #4

Small, somewhat nit-picky critique: the man pages for system calls are in section 2. If you want to see the docs for the "read()" syscall, and not the bash builtin "read", saying "man read" w̶o̶n̶'̶t̶ may not (see follow-up) do what you expect. Instead, you should say man 2 read This should probably be mentioned somewhere. Otherwise, great writeup. Thanks for sharing! (edited)

This is why the documentation for COHERENT was changed from "man" pages to what we called a Lexicon, removing the concept of sections. Each entry would have the description of the type of the entry, such as system call, shell command, and so on. Steve Ness has made this available online at http://www.nesssoftware.com/home/mwc/manual.php
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