include() and require() are also limited by safe mode.

Many filesystem-related functions are not appropriately restricted when
Safe Mode is activated on an NT server it seems.  I would assume that this
is due to the filesystem not making use of UID.

In all of my scripts, no matter WHO owns the script (file Ownership-wise)
or WHO owns the directory/file in question; both UIDs display

(getmyuid() and fileowner()) as UID = 0

This has the rather nasty side effect of Safe Mode allowing multiple
filesystem operations because it believes the script owner and file/dir
owner are one and the same.

While this can be worked around by the judicious application of proper
filesystem privileges, it's still a "dud" that many of Safe
Mode's securities are simply not there with an NT implementation.

If you do virutal hosting, you can turn safe mode on and off for different
Apache Virutal Hosts using the php_admin_value directive. This also allows
you to have customised maximum execution times, disabled functions, etc.
By placeing a base_dir for each virutal host, this means PHP CANNOT access
files below this heirachy; strongly recoomended for cutsomer hosting.

Eg:

[VirtualHost 127.0.0.1:80]
   DocumentRoot /var/www/html/safephphost/
   ServerName safephp
   php_admin_value safe_mode 1
   php_admin_value open_basedir /var/www/html/safephphost/
   php_admin_value sendmail_from phobo#paradise.net.nz
[/VirtualHost]

Just to note, I created patch which allows VirtualHost to set User under
which all (PHP too) runs. It is more secure than safe_mode. See
luxik.cdi.cz/~devik/apache/ if you are interested

All the filesystem-related functions (unlink, fopen, unlink, etc) seems to
be restricted the same way in safe mode, at least on PHP 4.2. If the file
UID is different *but* the directory (where the file is located) UID is
the same, it will work.

So creating a directory in safe mode is usually a bad idea since the UID
will be different from the script (it will be the apache UID) so it won't
be possible to do anything with the files created on this directory.

This is just a reply to phobo#paradise.net.nz about the virtual server. 
This no longer works on apache, if you do try you will get:
Syntax error on line 1118 of /usr/www/conf/httpd.conf:
php_admin_value not allowed here

You can a vhost.conf file.

<Directory /vhosts/domain.com/httpdocs/> 
php_admin_value safe_mode 0
php_admin_value open_basedir "/"
</Directory>

disable_functions must use "=" operator to assign value. Please
correct exemple.

[email protected] wrote in his comment of  02-Oct-2001 07:21: "By
placeing a base_dir for each virutal host, this means PHP CANNOT access
files below this heirachy"

"below" or "above" is obviously a matter of
visualization. The way I understand open_basedir is if you add an
open_basedir clause as in the example provided, php is ONLY able to access
files under the /var/www/html/safephphost/ directory. In other words php
will not be able to access /var/www/html/anotherfile but will be able to
access /var/www/html/safephphost/somefile.

Also - if  I understand correctly you do not need "safe_mode on"
when you have an open_basedir clause. (ref: 
"If instead of safe_mode, you set an open_basedir directory then all
file operations will be limited to files under the specified
directory")

Had to run ImageJPEG() and ImagePNG() out of safe mode in order to finally
get them to work.  My site is on a machine that uses Linux, PHP 4.1.2, GD
1.6.2 and employs safe mode. To get out of safe mode, had to name the 
script with a .cgi extension and insert  #!/usr/bin/php line at top of
script.

open_basedir only restricts file operations to files and directories under
a specified directory, but you can still user system ("vi
/home/somedir/somefile"), so safe_mode still has a place here as it
is much more restrictive then open_basedir.

Also, to reply to someone who said that 'above' and 'below' was a matter
of perspective, sure it is. Of course, a file is not under another one,
etc, it just pointed by some inode. But in the common language we consider
the root (/) to be above everything else, and /home is below root, and
/home/myfile is below /home. There is no written standard, but most people
(those I know anyway) agree on that syntax.