即使具有完全打开的权限，PHP fopen() 也会对文件失败

I'm currently migrating my LAMP from my Windows Server to a VPS running Debian 6. Most everything is working, however, one of the PHP scripts was failing to write to its configured log file. I could not determine why, so I wrote a new, simple, contrived PHP script to test the problem.

<?php
        ini_set('display_errors', 1);
        error_reporting(E_ALL);
        echo exec('whoami');
        $log = fopen('/var/log/apache2/writetest/writetest.log', 'a');
        if ($log != NULL)
        {
                fflush($log);
                fclose($log);
                $log = NULL;
        }
?>

然而，它失败了:

www-data Warning: fopen(/var/log/apache2/writetest/writetest.log): failed to open stream: Permission denied in /var/www/_admin/phpwritetest.php on line 5 

• 虽然我通常不会这样做，但为了帮助诊断，我将 /var/log/apache2/writetest/writetest.log 设置为 chmod 777.
• 目录和文件都归www-data:www-data所有.
• 该文件是使用 touch 创建的.
• While I would never do it normally, to help diagnose, I set /var/log/apache2/writetest/writetest.log to chmod 777.
• Both the directory and the file are owned by www-data:www-data.
• The file was created with touch.

我运行 strace 来验证哪个进程正在执行打开:

I ran strace to verify which process was performing the open:

[pid 21931] lstat("/var/log/apache2/writetest/writetest.log", 0x7fff81677d30) = -1 EACCES (Permission denied)
[pid 21931] lstat("/var/log/apache2/writetest", 0x7fff81677b90) = -1 EACCES (Permission denied)
[pid 21931] open("/var/log/apache2/writetest/writetest.log", O_RDWR|O_CREAT|O_TRUNC, 0666) = -1 EACCES (Permission denied)

我检查了一下，pid 21931 确实是 www-data 下运行的 apache2 子进程之一.如您所见，我还在脚本中包含了 echo exec('whoami'); ，以确认脚本正在由 www-data 运行.

I checked and pid 21931 was indeed one of the apache2 child processes running under www-data. As you can see, I also included echo exec('whoami'); in the script which confirmed the script was being run by www-data.

其他注意事项:

• PHP 未在安全模式下运行
• PHP open_basedir 未设置
• 版本信息:Apache/2.2.16 (Debian) PHP/5.3.3-7+squeeze3 with Suhosin-Patch mod_ssl/2.2.16 OpenSSL/0.9.8o
• uname -a: 2.6.32-238.19.1.el5.028stab092.2 #1 SMP Thu Jul 21 19:23:22 MSD 2011 x86_64 GNU/Linux
• 这是在 OpenVZ 下运行的 VPS 上
• ls -l (file): -rwxrwxrwx 1 www-data www-data 0 Sep 8 18:13 writetest.log
• ls -l(目录):drwxr-xr-x 2 www-data www-data 4096 Sep 8 18:13 writetest
• Apache2的父进程运行在root下，子进程运行在www-data
• selinux 未安装(感谢 Fabio 提醒我提及这一点)
• 我已经多次重启 apache 并重启服务器
• PHP is not running in safe mode
• PHP open_basedir is not set
• Version info: Apache/2.2.16 (Debian) PHP/5.3.3-7+squeeze3 with Suhosin-Patch mod_ssl/2.2.16 OpenSSL/0.9.8o
• uname -a: 2.6.32-238.19.1.el5.028stab092.2 #1 SMP Thu Jul 21 19:23:22 MSD 2011 x86_64 GNU/Linux
• This is on a VPS running under OpenVZ
• ls -l (file): -rwxrwxrwx 1 www-data www-data 0 Sep 8 18:13 writetest.log
• ls -l (directory): drwxr-xr-x 2 www-data www-data 4096 Sep 8 18:13 writetest
• Apache2's parent process runs under root, and the child processes under www-data
• selinux is not installed (thanks to Fabio for reminding me to mention this)
• I have restarted apache many times and rebooted the server as well

推荐答案

请记住，为了访问文件，所有父目录必须可以被 www-data 读取.您的 strace 输出似乎表明即使 accessing /var/log/apache2/writetest 也失败了.确保 www-data 对以下目录具有权限:

Remember that in order to reach a file, ALL parent directories must be readable by www-data. You strace output seems to indicate that even accessing /var/log/apache2/writetest is failing. Make sure that www-data has permissions on the following directories:

• /(r-x)
• /var (r-x)
• /var/log (r-x)
• /var/log/apache2 (r-x)
• /var/log/apache2/writetest (rwx)
• /var/log/apache2/writetest/writetest.log (rw-)