nixCraft Linux Sys Admin Blog

valgrind - Linux Tools For Debugging And Profiling Programs ( bug reporting tool )

Posted: 15 Apr 2008 07:21 PM CDT

Few days back I wrote about strace tool for reporting and finding bug in program. Today I'm going to talk about another interesting tool called valgrind.

Valgrind is a flexible program for debugging and profiling Linux executables. It consists of a core, which provides a synthetic CPU in software, and a series of "tools", each of which is a debugging or profiling tool. The architecture is modular, so that new tools can be created easily and without disturbing the existing structure. There are Valgrind tools that can automatically detect many memory management and threading bugs, and profile your programs in detail. You can also use Valgrind to build new tools.

The Valgrind distribution currently includes five production-quality tools:

a memory error detector
a thread error detector
a cache and branch-prediction profiler
a call-graph generating cache profiler
a heap profiler

It also includes two experimental tools:

a data race detector
an instant memory leak detector.

It runs on the following platforms:

X86/Linux
AMD64/Linux
PPC32/Linux
PPC64/Linux

How do I use valgrind?

Valgrind is typically run as follows:
$ valgrind command-name arg1 arg2 argN $ valgrind program args $ valgrind ./myapp -d /tmp -f 120
You can select tool using the --tool=TOOLName option. For example use memcheck which is a fine-grained memory checker. To generate trace back for command called myapp, enter:
$ valgrind --tool=memcheck -v --log-file=myapp.dbg --num-callers=8 ./myapp -d /tmp -f 120
Where,

--tool=memcheck : Run the Valgrind tool called memcheck
-v : Verbose output
--log-file=myapp.dbg : Specifies that Valgrind should send all of its messages to the specified file.
--num-callers=8 : By default, Valgrind shows twelve levels of function call names to help you identify program locations. You can change that number with this option. This can help in determining the programâ€™s location in deeply-nested call chains.

The --leak-check option turns on the detailed memory leak detector:
$ valgrind --tool=memcheck -v --log-file=myapp.dbg --num-callers=8 --leak-check=yes ./myapp -d /tmp -f 120

URL Format

The generated URL has to have the format:

<uri-prefix>/<token>/<timestamp-in-hex>/<rel-path>

Which looks like
http://theos.in/dl/6262df3adba2bc85846e05440fcc3895/4804f986/file.zip

is an MD5 of

a secret string (user supplied)
<rel-path> (starts with /)
<timestamp-in-hex>

Understanding filesystem layout

Domain name: theos.in
Webroot : /home/lighttpd/theos.in/http/
Download location : /home/lighttpd/download-area/ (you must upload all download files here)
Download url : http://theos.in/dl/<token>/<timestamp-in-hex>/file.zip

Make sure /home/lighttpd/download-area/ directory exists:
# mkdir -p /home/lighttpd/download-area/ # chown lighttpd:lighttpd /home/lighttpd/download-area/

Configuration

Open lighttpd.conf file:
# vi /etc/lighttpd/lighttpd.conf
Append following configuration:

secdownload.secret          = "MySecretSecurePassword" secdownload.document-root   = "/home/lighttpd/download-area/" secdownload.uri-prefix      = "/dl/" secdownload.timeout         = 3600

Where.

secdownload.secret : Your password; it must not be shared with anyone else
secdownload.document-root : Download file system location, must be outside domain webroot / documentroot
secdownload.uri-prefix : url prefix such as /dl/ or /download/
secdownload.timeout : Set timeout for each unique url in seconds

Save and close the file. Restart lighttpd:
# service lighttpd restart

Sample PHP Download Script

<?php $secret = "MySecretSecurePassword"; $uri_prefix = "/dl/";   # set filename $f = "/file.zip";   # set current timestamp $t = time(); $t_hex = sprintf("%08x", $t); $m = md5($secret.$f.$t_hex); # finally generate link and display back on screen printf('<a href="%s%s/%s%s" class="broken_link">%s</a>',$uri_prefix, $m, $t_hex, $f, $f); ?>

410 Gone HTTP Error Code

After timeout; unique url will be gone and end user will get 410 http status code. It indicates that the resource requested is no longer available and will not be available again. So if anybody deeplinked or hotlinked your content it will be gone after timeout.