PHP 的session是一個非常難以琢磨的問題。
如果不明白session跨目錄是什麼問題，可以自行百度，或者不繼續閱讀，我就不描述問題了。只有遇到問題，琢磨不明白的時候，你就讀讀這篇
我們首先來看看 php.ini 中對 session 的配置，估計你平時沒注意到 session 會有這麼多的設置內容：
[Session]
; Handler used to store/retrieve data.
; http://php.net/session.save-handler
session.save_handler = redis
; 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.
;
; The path can be defined 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
; your OS has problems with many files in one directory, and is
; a more efficient layout for servers that handle many 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.
; http://php.net/session.save-path
;session.save_path = "/tmp"
session.save_path = "tcp://127.0.0.1:6379"
; Whether to use strict session mode.
; Strict session mode does not accept uninitialized session ID and regenerate
; session ID if browser sends uninitialized session ID. Strict mode protects
; applications from session fixation via session adoption vulnerability. It is
; disabled by default for maximum compatibility, but enabling it is encouraged.
; https://wiki.php.net/rfc/strict_sessions
session.use_strict_mode = 0
; Whether to use cookies.
; http://php.net/session.use-cookies
session.use_cookies = 1
; http://php.net/session.cookie-secure
;session.cookie_secure =
; This option forces PHP to fetch and use a cookie for storing and maintaining
; the session id. We encourage this operation as it's very helpful in combating
; session hijacking when not specifying and managing your own session id. It is
; not the be-all and end-all of session hijacking defense, but it's a good start.
; http://php.net/session.use-only-cookies
session.use_only_cookies = 1
; Name of the session (used as cookie name).
; http://php.net/session.name
session.name = PHPSESSID
; Initialize session on request startup.
; http://php.net/session.auto-start
session.auto_start = 1
; Lifetime in seconds of cookie or, if 0, until browser is restarted.
; http://php.net/session.cookie-lifetime
session.cookie_lifetime = 0
; The path for which the cookie is valid.
; http://php.net/session.cookie-path
session.cookie_path = /
; The domain for which the cookie is valid.
; http://php.net/session.cookie-domain
session.cookie_domain =
; Whether or not to add the httpOnly flag to the cookie, which makes it inaccessible to browser scripting languages such as JavaScript.
; http://php.net/session.cookie-httponly
session.cookie_httponly =
; Handler used to serialize data. php is the standard serializer of PHP.
; http://php.net/session.serialize-handler
session.serialize_handler = php
; Defines the probability that the 'garbage collection' process is started
; on every session initialization. The probability is calculated by using
; gc_probability/gc_divisor. Where session.gc_probability is the numerator
; and gc_divisor is the denominator in the equation. Setting this value to 1
; when the session.gc_divisor value is 100 will give you approximately a 1% chance
; the gc will run on any give request.
; Default Value: 1
; Development Value: 1
; Production Value: 1
; http://php.net/session.gc-probability
session.gc_probability = 1
; Defines the probability that the 'garbage collection' process is started on every
; session initialization. The probability is calculated by using the following equation:
; gc_probability/gc_divisor. Where session.gc_probability is the numerator and
; session.gc_divisor is the denominator in the equation. Setting this value to 1
; when the session.gc_divisor value is 100 will give you approximately a 1% chance
; the gc will run on any give request. Increasing this value to 1000 will give you
; a 0.1% chance the gc will run on any give request. For high volume production servers,
; this is a more efficient approach.
; Default Value: 100
; Development Value: 1000
; Production Value: 1000
; http://php.net/session.gc-divisor
session.gc_divisor = 1000
; After this number of seconds, stored data will be seen as 'garbage' and
; cleaned up by the garbage collection process.
; http://php.net/session.gc-maxlifetime
session.gc_maxlifetime = 1440
; NOTE: If you are using the subdirectory option for storing session files
; (see session.save_path above), then garbage collection does *not*
; happen automatically. You will need to do your own garbage
; collection through a shell script, cron entry, or some other method.
; For example, the following script would is the equivalent of
; setting session.gc_maxlifetime to 1440 (1440 seconds = 24 minutes):
; find /path/to/sessions -cmin +24 -type f | xargs rm
; Check HTTP Referer to invalidate externally stored URLs containing ids.
; HTTP_REFERER has to contain this substring for the session to be
; considered as valid.
; http://php.net/session.referer-check
session.referer_check =
; How many bytes to read from the file.
; http://php.net/session.entropy-length
;session.entropy_length = 32
; Specified here to create the session id.
; http://php.net/session.entropy-file
; Defaults to /dev/urandom
; On systems that don't have /dev/urandom but do have /dev/arandom, this will default to /dev/arandom
; If neither are found at compile time, the default is no entropy file.
; On windows, setting the entropy_length setting will activate the
; Windows random source (using the CryptoAPI)
;session.entropy_file = /dev/urandom
; Set to {nocache,private,public,} to determine HTTP caching aspects
; or leave this empty to avoid sending anti-caching headers.
; http://php.net/session.cache-limiter
session.cache_limiter = nocache
; Document expires after n minutes.
; http://php.net/session.cache-expire
session.cache_expire = 180
; trans sid support is disabled by default.
; Use of trans sid may risk your users' security.
; Use this option with caution.
; - User may send URL contains active session ID
; to other person via. email/irc/etc.
; - URL that contains active session ID may be stored
; in publicly accessible computer.
; - User may access your site with the same session ID
; always using URL stored in browser's history or bookmarks.
; http://php.net/session.use-trans-sid
session.use_trans_sid = 1
; Select a hash function for use in generating session ids.
; Possible Values
; 0 (MD5 128 bits)
; 1 (SHA-1 160 bits)
; This option may also be set to the name of any hash function supported by
; the hash extension. A list of available hashes is returned by the hash_algos()
; function.
; http://php.net/session.hash-function
session.hash_function = 0
; Define how many bits are stored in each character when converting
; the binary hash data to something readable.
; Possible values:
; 4 (4 bits: 0-9, a-f)
; 5 (5 bits: 0-9, a-v)
; 6 (6 bits: 0-9, a-z, A-Z, "-", ",")
; Default Value: 4
; Development Value: 5
; Production Value: 5
; http://php.net/session.hash-bits-per-character
session.hash_bits_per_character = 5
; The URL rewriter will look for URLs in a defined set of HTML tags.
; form/fieldset are special; if you include them here, the rewriter will
; add a hidden <input> field with the info which is otherwise appended
; to URLs. If you want XHTML conformity, remove the form entry.
; Note that all valid entries require a "=", even if no value follows.
; Default Value: "a=href,area=href,frame=src,form=,fieldset="
; Development Value: "a=href,area=href,frame=src,input=src,form=fakeentry"
; Production Value: "a=href,area=href,frame=src,input=src,form=fakeentry"
; http://php.net/url-rewriter.tags
url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=fakeentry"
; Enable upload progress tracking in $_SESSION
; Default Value: On
; Development Value: On
; Production Value: On
; http://php.net/session.upload-progress.enabled
;session.upload_progress.enabled = On
; Cleanup the progress information as soon as all POST data has been read
; (i.e. upload completed).
; Default Value: On
; Development Value: On
; Production Value: On
; http://php.net/session.upload-progress.cleanup
;session.upload_progress.cleanup = On
; A prefix used for the upload progress key in $_SESSION
; Default Value: "upload_progress_"
; Development Value: "upload_progress_"
; Production Value: "upload_progress_"
; http://php.net/session.upload-progress.prefix
;session.upload_progress.prefix = "upload_progress_"
; The index name (concatenated with the prefix) in $_SESSION
; containing the upload progress information
; Default Value: "PHP_SESSION_UPLOAD_PROGRESS"
; Development Value: "PHP_SESSION_UPLOAD_PROGRESS"
; Production Value: "PHP_SESSION_UPLOAD_PROGRESS"
; http://php.net/session.upload-progress.name
;session.upload_progress.name = "PHP_SESSION_UPLOAD_PROGRESS"
; How frequently the upload progress should be updated.
; Given either in percentages (per-file), or in bytes
; Default Value: "1%"
; Development Value: "1%"
; Production Value: "1%"
; http://php.net/session.upload-progress.freq
;session.upload_progress.freq = "1%"
; The minimum delay between updates, in seconds
; Default Value: 1
; Development Value: 1
; Production Value: 1
; http://php.net/session.upload-progress.min-freq
;session.upload_progress.min_freq = "1"
php 對session的配置比較多，設計到跨目錄的，就這麼幾個：
# 一定要保證 save_path 有寫入權限，否則，session 不生效
session.save_path
# 是否使用 cookie,保存 phpsessinid
session.use_cookies = 1
# 是否只使用 cookies
session.use_only_cookies = 1
# 是否使用url模式傳遞sessionid，這個可以不配置
session.use_trans_sid = 1
# sessionid，每個頁面保持一致，否則取不到cookie，特別是多個框架混合的項目，一定要保持一致
session.name = PHPSESSID
# 是否自動打開cookie
session.auto_start = 1
# sessionid 這個cookie 的path，最好用 更目錄，這樣每個子目錄都能訪問到
session.cookie_path = /
# cookie 的域名，需要保持一致。只要保持一致，多域名的模式照樣能訪問（當然要用根域名）
session.cookie_domain =
遇到問題不要慌，挨個檢查上面的幾個參數，另外，session 配置 radis 也非常簡單，在寶塔中可以直接配置。