Description:
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Normal session file can be generated in session.save_path,but the length of all session files is 0.No session data can be saved in session file.

The following is my phpinfo():
Session Support 	enabled
Registered save handlers 	files user sqlite
Registered serializer handlers 	php php_binary

Directive	Local Value	Master Value
session.auto_start	Off	Off
session.bug_compat_42	Off	Off
session.bug_compat_warn	On	On
session.cache_expire	180	180
session.cache_limiter	nocache	nocache
session.cookie_domain	no value	no value
session.cookie_httponly	Off	Off
session.cookie_lifetime	0	0
session.cookie_path	/	/
session.cookie_secure	Off	Off
session.entropy_file	no value	no value
session.entropy_length	0	0
session.gc_divisor	1000	1000
session.gc_maxlifetime	1440	1440
session.gc_probability	1	1
session.hash_bits_per_character	5	5
session.hash_function	0	0
session.name	PHPSESSID	PHPSESSID
session.referer_check	no value	no value
session.save_handler	files	files
session.save_path	/var/lib/php	/var/lib/php
session.serialize_handler	php	php
session.use_cookies	On	On
session.use_only_cookies	Off	Off
session.use_trans_sid	0	0


I'm sure the Directory session.save_path is writable(it's tested using PHP Function 'is_writable').