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7 years ago
I recently made an interesting observation:

It seems that `session_start()` can return `true` even if the session was not properly created. In my case, the disk storage was full and so the session data could not be written to disk. I had some logic that resulted in an infinite loop when the session was not written to disk.

To check if the session really was saved to disk I used:

```
<?php

function safe_session_start() {
    # Attempt to start a session
    if (!@\session_start()) return false;

    #
    # Check if we need to perform
    # the write test.
    #
    if (!isset($_SESSION['__validated'])) {
        $_SESSION['__validated'] = 1;

        # Attempt to write session to disk
        @\session_write_close();

        # Unset the variable from memory.
        # This step may be unnecessary
        unset($_SESSION['__validated']);

        # Re-start session
        @\session_start();

        # Check if variable value is retained
        if (!isset($_SESSION['__validated'])) {
            # Session was not written to disk
            return false;
        }
    }

    return true;
}

if (!safe_session_start()) {
    # Sessions are probably not written to disk...
    # Handle error accordingly.
}

?>
```

Took me quite a while to figure this out. 

Maybe it helps someone!
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