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+Contributor:	Andrew Tridgell <samba@samba.org>
+Date:		Old
+Status:		Questionable
+
+Subject:	How to trace samba system calls for debugging purposes
+=============================================================================
+
+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.
+
+Actually its not as bad as the the above makes it sound, just don't
+expect the output to be very pretty :-)
+
+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. 
+
+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. 
+
+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.
+
+Next, try using strace on some simple commands. For example, "strace
+ls" or "strace echo hello".
+
+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!)
+
+For example, the only line that really matters in the "strace echo
+hello" output is:
+
+write(1, "hello\n", 6)                  = 6
+
+all the rest is just setting up to run the program.
+
+Ok, now you're famialiar 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
+"strace -p PID" 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:
+
+  strace -f -p 3872 >& strace.out
+
+or with a sh style shell:
+
+  strace -f -p 3872 > strace.out 2>&1
+
+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.
+
+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. 
+
+So how do you interpret the results? Generally I search thorugh 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.
+
+Beyond this you will have to use your initiative. To give you an idea
+of wehat you are looking for here is a piece of strace output that
+shows that /dev/null is not world writeable, which causes printing to
+fail with Samba:
+
+[pid 28268] open("/dev/null", O_RDWR)   = -1 EACCES (Permission denied)
+[pid 28268] open("/dev/null", O_WRONLY) = -1 EACCES (Permission denied)
+
+the process is trying to first open /dev/null read-write then
+read-only. Both fail. This means /dev/null has incorrect permissions.
+
+Have fun!
+
+(please send updates/fixes to this file to samba@samba.org)