PHP Sessions Timing Out Too Quickly

PHP sessions timing out too quickly

Random expiration is a classical symptom of session data directory shared by several applications: the one with the shortest session.gc_maxlifetime time is likely to remove data from other applications. The reason:

1. PHP stores session files in the system temporary directory by default.

2. The builtin file handler doesn't track who owns what session file (it just matches file name with session ID):

   

My advice is that you configure a private custom session directory for your application. That can be done with the session_save_path() function or setting the session.save_path configuration directive. Please check your framework's documentation for the precise details on how to do it in your own codebase.

PHP Session Timing Out Soon

After so many attempts, What worked was we have to change the session path to "/tmp" on .htaccess. This is how it would seem to work if the app is hosted in a shared hosting.

PHP Sessions expire too soon

This sounds a bit like Ubuntu or Debian on the server. If I rememeber correctly there is a cronjob somewhere (installed either by the php5 or the php5-common package) which cleans out your session directory more often.

I'd recommend you configure your sessions to be saved somewhere else (than the default). Adjust session.save_path and verify to cronjob doesn't empty it.

The cronjob is somewhere like /etc/cron.d/php - to be certain, run dpkg -L php5 or dpkg -L php5-common. Assuming you are on Ubuntu (or Debian) this should show you the location of all installed files.

why is my PHP session expiring prematurely?

There are many possible reasons why session data is not being correctly handled. Most likely, the session is not being started on EVERY page that is loaded and uses the data. To fix this, make sure that session_start() is started on every single page that is called or redirected to. Also, if you make any changes to the session configuration (ex, ini_set()), make sure that that is applied either globally or on each any every page. To apply it globally, add

php_flag session.gc_maxlifetime <your value>
php_flag session.cache_expire <your value>

to your .htaccess file. Alternatively, you can add

ini_set("session.gc_maxlifetime", <value>);
ini_set("session.cache_expire", <value>);

directly before session_start() on every page that calls session_start().

How to change the session timeout in PHP?

Session timeout is a notion that has to be implemented in code if you want strict guarantees; that's the only way you can be absolutely certain that no session ever will survive after X minutes of inactivity.

If relaxing this requirement a little is acceptable and you are fine with placing a lower bound instead of a strict limit to the duration, you can do so easily and without writing custom logic.

Convenience in relaxed environments: how and why

If your sessions are implemented with cookies (which they probably are), and if the clients are not malicious, you can set an upper bound on the session duration by tweaking certain parameters. If you are using PHP's default session handling with cookies, setting session.gc_maxlifetime along with session_set_cookie_params should work for you like this:

// server should keep session data for AT LEAST 1 hour
ini_set('session.gc_maxlifetime', 3600);

// each client should remember their session id for EXACTLY 1 hour
session_set_cookie_params(3600);

session_start(); // ready to go!

This works by configuring the server to keep session data around for at least one hour of inactivity and instructing your clients that they should "forget" their session id after the same time span. Both of these steps are required to achieve the expected result.

• If you don't tell the clients to forget their session id after an hour (or if the clients are malicious and choose to ignore your instructions) they will keep using the same session id and its effective duration will be non-deterministic. That is because sessions whose lifetime has expired on the server side are not garbage-collected immediately but only whenever the session GC kicks in.

  GC is a potentially expensive process, so typically the probability is rather small or even zero (a website getting huge numbers of hits will probably forgo probabilistic GC entirely and schedule it to happen in the background every X minutes). In both cases (assuming non-cooperating clients) the lower bound for effective session lifetimes will be session.gc_maxlifetime, but the upper bound will be unpredictable.

• If you don't set session.gc_maxlifetime to the same time span then the server might discard idle session data earlier than that; in this case, a client that still remembers their session id will present it but the server will find no data associated with that session, effectively behaving as if the session had just started.

Certainty in critical environments

You can make things completely controllable by using custom logic to also place an upper bound on session inactivity; together with the lower bound from above this results in a strict setting.

Do this by saving the upper bound together with the rest of the session data:

session_start(); // ready to go!

$now = time();
if (isset($_SESSION['discard_after']) && $now > $_SESSION['discard_after']) {
    // this session has worn out its welcome; kill it and start a brand new one
    session_unset();
    session_destroy();
    session_start();
}

// either new or old, it should live at most for another hour
$_SESSION['discard_after'] = $now + 3600;

Session id persistence

So far we have not been concerned at all with the exact values of each session id, only with the requirement that the data should exist as long as we need them to. Be aware that in the (unlikely) case that session ids matter to you, care must be taken to regenerate them with session_regenerate_id when required.

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