diff options
| author | vorlon <vorlon@alioth.debian.org> | 2007-11-21 17:29:21 +0000 |
|---|---|---|
| committer | vorlon <vorlon@alioth.debian.org> | 2007-11-21 17:29:21 +0000 |
| commit | 58b37572718ed65d1b143f44de16aa5efb512f11 (patch) | |
| tree | 96694e5871586bd21d9b2b91f9a277111ace0812 /docs/htmldocs/Samba3-Developers-Guide/tracing.html | |
| parent | f24db2434a26f04e1761c6dbde69d4be999a1cfc (diff) | |
| download | samba-58b37572718ed65d1b143f44de16aa5efb512f11.tar.gz | |
Load samba-3.0.27a into branches/upstream.upstream/3.0.27a
git-svn-id: svn://svn.debian.org/svn/pkg-samba/branches/upstream@1583 fc4039ab-9d04-0410-8cac-899223bdd6b0
Diffstat (limited to 'docs/htmldocs/Samba3-Developers-Guide/tracing.html')
| -rw-r--r-- | docs/htmldocs/Samba3-Developers-Guide/tracing.html | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/docs/htmldocs/Samba3-Developers-Guide/tracing.html b/docs/htmldocs/Samba3-Developers-Guide/tracing.html new file mode 100644 index 0000000000..32b5b78be2 --- /dev/null +++ b/docs/htmldocs/Samba3-Developers-Guide/tracing.html @@ -0,0 +1,77 @@ +<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 14. Tracing samba system calls</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.0"><link rel="start" href="index.html" title="SAMBA Developers Guide"><link rel="up" href="pt04.html" title="Part IV. Debugging and tracing"><link rel="prev" href="pt04.html" title="Part IV. Debugging and tracing"><link rel="next" href="devprinting.html" title="Chapter 15. Samba Printing Internals"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 14. Tracing samba system calls</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="pt04.html">Prev</a> </td><th width="60%" align="center">Part IV. Debugging and tracing</th><td width="20%" align="right"> <a accesskey="n" href="devprinting.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="tracing"></a>Chapter 14. Tracing samba system calls</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Andrew</span> <span class="surname">Tridgell</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span></div></div></div></div></div><p> +This file describes how to do a system call trace on Samba to work out +what its doing wrong. This is not for the faint of heart, but if you +are reading this then you are probably desperate. +</p><p> +Actually its not as bad as the the above makes it sound, just don't +expect the output to be very pretty :-) +</p><p> +Ok, down to business. One of the big advantages of unix systems is +that they nearly all come with a system trace utility that allows you +to monitor all system calls that a program is making. This is +extremely using for debugging and also helps when trying to work out +why something is slower than you expect. You can use system tracing +without any special compilation options. +</p><p> +The system trace utility is called different things on different +systems. On Linux systems its called strace. Under SunOS 4 its called +trace. Under SVR4 style systems (including solaris) its called +truss. Under many BSD systems its called ktrace. +</p><p> +The first thing you should do is read the man page for your native +system call tracer. In the discussion below I'll assume its called +strace as strace is the only portable system tracer (its available for +free for many unix types) and its also got some of the nicest +features. +</p><p> +Next, try using strace on some simple commands. For example, <code class="literal">strace +ls</code> or <code class="literal">strace echo hello</code>. +</p><p> +You'll notice that it produces a LOT of output. It is showing you the +arguments to every system call that the program makes and the +result. Very little happens in a program without a system call so you +get lots of output. You'll also find that it produces a lot of +"preamble" stuff showing the loading of shared libraries etc. Ignore +this (unless its going wrong!) +</p><p> +For example, the only line that really matters in the <code class="literal">strace echo +hello</code> output is: +</p><pre class="programlisting"> +write(1, "hello\n", 6) = 6 +</pre><p>all the rest is just setting up to run the program.</p><p> +Ok, now you're familiar with strace. To use it on Samba you need to +strace the running smbd daemon. The way I tend ot use it is to first +login from my Windows PC to the Samba server, then use smbstatus to +find which process ID that client is attached to, then as root I do +<code class="literal">strace -p PID</code> to attach to that process. I normally redirect the +stderr output from this command to a file for later perusal. For +example, if I'm using a csh style shell: +</p><p><code class="literal">strace -f -p 3872 >& strace.out</code></p><p>or with a sh style shell:</p><p><code class="literal">strace -f -p 3872 > strace.out 2>&1</code></p><p> +Note the "-f" option. This is only available on some systems, and +allows you to trace not just the current process, but any children it +forks. This is great for finding printing problems caused by the +"print command" being wrong. +</p><p> +Once you are attached you then can do whatever it is on the client +that is causing problems and you will capture all the system calls +that smbd makes. +</p><p> +So how do you interpret the results? Generally I search through the +output for strings that I know will appear when the problem +happens. For example, if I am having touble with permissions on a file +I would search for that files name in the strace output and look at +the surrounding lines. Another trick is to match up file descriptor +numbers and "follow" what happens to an open file until it is closed. +</p><p> +Beyond this you will have to use your initiative. To give you an idea +of what you are looking for here is a piece of strace output that +shows that <code class="filename">/dev/null</code> is not world writeable, which +causes printing to fail with Samba: +</p><pre class="programlisting"> +[pid 28268] open("/dev/null", O_RDWR) = -1 EACCES (Permission denied) +[pid 28268] open("/dev/null", O_WRONLY) = -1 EACCES (Permission denied) +</pre><p> +The process is trying to first open <code class="filename">/dev/null</code> read-write +then read-only. Both fail. This means <code class="filename">/dev/null</code> has +incorrect permissions. +</p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pt04.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="pt04.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="devprinting.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part IV. Debugging and tracing </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 15. Samba Printing Internals</td></tr></table></div></body></html> |