$ strace php tias.php -e open,access 2>&1 | <a class="zem_slink freebase/en/grep" href="http://en.wikipedia.org/wiki/Grep" title="Grep" rel="wikipedia">grep foo.txt Sometimes a program refuses to read a file and you&#8217;re not sure why. You may have display_errors turned off for <a class="zem_slink freebase/en/php" href="http://www.php.net/" title="PHP" rel="homepage">PHP or something. In this example, fopen(&#8217;/var/www/test/foo.txt&#8217;) was called but doesn&#8217;t have read access to foo.txt.

Strace can tell you what went wrong. E.g., if php doesn&#8217;t have read access to the file, strace will say &#8221;EACCESS (Permission denied)&#8221;. Or, if the <a class="zem_slink freebase/guid/9202a8c04000641f8000000000220ffa" href="http://en.wikipedia.org/wiki/Path_%28computing%29" title="Path (computing)" rel="wikipedia">file path you gave doesn&#8217;t exist, strace will say &#8221;ENOENT (No such file or directory)&#8221;, etc.

This works for any program you can run from the <a class="zem_slink freebase/en/command_line_interface" href="http://en.wikipedia.org/wiki/Command-line_interface" title="Command-line interface" rel="wikipedia">command-line, e.g., strace python myapp.py -e open,access…

Note: the above command uses php-cli, not mod_php, which is a different <a class="zem_slink freebase/en/server_application_programming_interface" href="http://en.wikipedia.org/wiki/Server_Application_Programming_Interface" title="Server Application Programming Interface" rel="wikipedia">SAPI with <a class="zem_slink freebase/en/diff" href="http://www.tracked.com/company/digg_inc/" title="Diff" rel="tracked">diff configs, etc.

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by David Winterbottom (<a href="http://codeinthehole.com">codeinthehole.com)

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