I found this is the php.ini file:
; Handler used to store/retrieve data.
session.save_handler = files
; Argument passed to save_handler. In the case of files, this is the path
; where data files are stored. Note: Windows users have to change this
; variable in order to use PHP's session functions.
; As of PHP 4.0.1, you can define the path as:
; session.save_path = "N;/path"
; where N is an integer. Instead of storing all the session files in
; /path, what this will do is use subdirectories N-levels deep, and
; store the session data in those directories. This is useful if you
; or your OS have problems with lots of files in one directory, and is
; a more efficient layout for servers that handle lots of sessions.
; NOTE 1: PHP will not create this directory structure automatically.
; You can use the script in the ext/session dir for that purpose.
; NOTE 2: See the section on garbage collection below if you choose to
; use subdirectories for session storage
; The file storage module creates files using mode 600 by default.
; You can change that by using
; session.save_path = "N;MODE;/path"
; where MODE is the octal representation of the mode. Note that this
; does not overwrite the process's umask.
;session.save_path = "/tmp"