php.ini中的safe_mode如下：
; Safe Mode
;
safe_mode = Off
; By default, Safe Mode does a UID compare check when
; opening files. If you want to relax this to a GID compare,
; then turn on safe_mode_gid.
safe_mode_gid = Off
; When safe_mode is on, UID/GID checks are bypassed when
; including files from this directory and its subdirectories.
; (directory must also be in include_path or full path must
; be used when including)
safe_mode_include_dir =
; When safe_mode is on, only executables located in the safe_mode_exec_dir
; will be allowed to be executed via the exec family of functions.
safe_mode_exec_dir =
; Setting certain environment variables may be a potential security breach.
; This directive contains a comma-delimited list of prefixes. In Safe Mode,
; the user may only alter environment variables whose names begin with the
; prefixes supplied here. By default, users will only be able to set
; environment variables that begin with PHP_ (e.g. PHP_FOO=BAR).
;
; Note: If this directive is empty, PHP will let the user modify ANY
; environment variable!
safe_mode_allowed_env_vars = PHP_
; This directive contains a comma-delimited list of environment variables that
; the end user won't be able to change using putenv(). These variables will be
; protected even if safe_mode_allowed_env_vars is set to allow to change them.
safe_mode_protected_env_vars = LD_LIBRARY_PATH
safe_mode 是一种安全模式，他提供了一个基本安全的共享环境，
在一个有多个用户账户存在的php开发的web服务器上。当安全模式打开的时候，一些函数将被完全的禁止，而另一些函数的功能将会受到限制，如：chdir,move_uploaded_file,chgrp,parse_ini_file,chown,rmdir,copy,rename,fopen,require,mkdir,unlink等。
注意，在php5.3以上版本，safe_mode被弃用，在php5.4以上版本，则将此特性完全去除了。
