Deep understanding of PHP principles-a small probability of Session Gc Notice

If PHP installed with apt is used in ubuntu/Debian, this prompt may be reported when Session is used. Copy codeThe Code is as follows: PHP Notice: session_start (): ps_files_cleanup_dir:
Opendir (/var/lib/php5) failed: Permission denied (13)
In/home/laruence/www/htdocs/index. php on line 22

This is because, in PHP, if file_handler is used as the save handler of the Session, the Gc process of the Session will be run at each session_start.Copy codeThe Code is as follows: // omitted
Int nrdels =-1;
Nrand = (int) (float) PS (gc_divisor) * php_combined_lcg (TSRMLS_C ));
If (nrand <PS (gc_probability )){
PS (mod)-> s_gc (& PS (mod_data), PS (gc_maxlifetime), & nrdels TSRMLS_CC );
}
// Omitted

The cause of this warning is that in apt PHP, the default session directory/var/lib/php5 has the permission of 733 with sticky bit, that isCopy codeThe Code is as follows: drwx-wx-wt root roo

Generally, PHP worker runs in a non-root identity, so it does not have the permission to open this folder (but because it can be written, it does not affect normal Session file reading ). the following code in s_gc triggers the Notice mentioned at the beginning:Copy codeThe Code is as follows: // for file handler, s_gc indirectly calls ps_files_cleanup_dir:
Dir = opendir (dirname );
If (! Dir ){
Php_error_docref (NULL TSRMLS_CC, E_NOTICE,
"Ps_files_cleanup_dir: opendir (% s) failed: % s (% d )",
Dirname, strerror (errno), errno );
Return (0 );
}

Of course, gc is still available in ubuntu/Debian, but it is completed by external cron processes. The default value is/etc/cron. d/php5 :,Copy codeThe Code is as follows: * 39 * root [-x/usr/lib/php5/maxlifetime]
& [-D/var/lib/php5] & find/var/lib/php5/
-Type f-cmin + $(/usr/lib/php5/maxlifetime)-print0
| Xargs-n 200-r-0 r

In addition, we can see that when determining whether s_gc is running, there are two key variables: PS (gc_divisor) and PS (gc_probability ), these two variables correspond to the two same-name configuration items of the session runtime configuration item respectively:
Session. gc_probability and session. gc_divisor. The default values are 1 and 100, respectively.
Php_combined_lcg is a random number generator that generates a random number ranging from 0 to 1. Therefore, the above discrimination is equivalent:Copy codeThe Code is as follows: rand <probability/gc_diviso

That is to say, by default, the gc process can be called almost 100 times. Therefore, the Notice can be seen at a low probability.
To disable this Notice, you only need to set:
Session. gc_probability = 0, so that s_gc has no possibility of running.
Of course, you can also change the permissions of this folder...
Finally, I would like to thank CFC4N for providing this question.
Author: Laruence ()
Address: http://www.laruence.com/2011/03/29/1949.html