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diff --git a/docs/docbook/devdoc/Tracing.xml b/docs/docbook/devdoc/Tracing.xml deleted file mode 100644 index ccf1e1c3c8..0000000000 --- a/docs/docbook/devdoc/Tracing.xml +++ /dev/null @@ -1,129 +0,0 @@ -<chapter id="tracing"> -<chapterinfo> - <author> - <firstname>Andrew</firstname><surname>Tridgell</surname> - <affiliation> - <orgname>Samba Team</orgname> - </affiliation> - </author> -</chapterinfo> - -<title>Tracing samba system calls</title> - -<para> -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. -</para> - -<para> -Actually its not as bad as the the above makes it sound, just don't -expect the output to be very pretty :-) -</para> - -<para> -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. -</para> - -<para> -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. -</para> - -<para> -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. -</para> - -<para> -Next, try using strace on some simple commands. For example, <command>strace -ls</command> or <command>strace echo hello</command>. -</para> - -<para> -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!) -</para> - -<para> -For example, the only line that really matters in the <command>strace echo -hello</command> output is: -</para> - -<para><programlisting> -write(1, "hello\n", 6) = 6 -</programlisting></para> - -<para>all the rest is just setting up to run the program.</para> - -<para> -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 -<command>strace -p PID</command> 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: -</para> - -<para><command>strace -f -p 3872 >& strace.out</command></para> - -<para>or with a sh style shell:</para> - -<para><command>strace -f -p 3872 > strace.out 2>&1</command></para> - -<para> -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. -</para> - -<para> -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. -</para> - -<para> -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. -</para> - -<para> -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 <filename>/dev/null</filename> is not world writeable, which -causes printing to fail with Samba: -</para> - -<para><programlisting> -[pid 28268] open("/dev/null", O_RDWR) = -1 EACCES (Permission denied) -[pid 28268] open("/dev/null", O_WRONLY) = -1 EACCES (Permission denied) -</programlisting></para> - -<para> -The process is trying to first open <filename>/dev/null</filename> read-write -then read-only. Both fail. This means <filename>/dev/null</filename> has -incorrect permissions. -</para> - -</chapter> |