php man page for uniqid

UNIQID(3)								 1								 UNIQID(3)

uniqid - Generate a unique ID

SYNOPSIS
       string uniqid ([string  $prefix = ""], [bool  $more_entropy = false])

DESCRIPTION
	Gets a prefixed unique identifier based on the current time in microseconds.

       Warning

	       This  function does not create random nor unpredictable strings.  This function must not be used for security purposes. Use a cryp-
	      tographically secure random function/generator and cryptographically secure hash functions to create unpredictable secure IDs.

PARAMETERS
	      o $prefix
		- Can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the iden-
		tifier	at the same microsecond.  With an empty $prefix, the returned string will be 13 characters long. If $more_entropy is TRUE,
		it will be 23 characters.

	      o $more_entropy
		- If set to TRUE, uniqid(3) will add additional entropy (using the combined linear congruential  generator)  at  the  end  of  the
		return value, which increases the likelihood that the result will be unique.

RETURN VALUES
	Returns the unique identifier, as a string.

EXAMPLES
       Example #1

	      uniqid(3) Example

	      <?php
	      /* A uniqid, like: 4b3403665fea6 */
	      printf("uniqid(): %s
", uniqid());

	      /* We can also prefix the uniqid, this the same as
	       * doing:
	       *
	       * $uniqid = $prefix . uniqid();
	       * $uniqid = uniqid($prefix);
	       */
	      printf("uniqid('php_'): %s
", uniqid('php_'));

	      /* We can also activate the more_entropy parameter, which is
	       * required on some systems, like Cygwin. This makes uniqid()
	       * produce a value like: 4b340550242239.64159797
	       */
	      printf("uniqid('', true): %s
", uniqid('', true));
	      ?>

NOTES
       Caution

	       This  function does not generate cryptographically secure tokens, in fact without being passed any additional parameters the return
	      value  is  little  different  from  microtime(3).  If  you  need	to  generate  cryptographically  secure  tokens  use  openssl_ran-
	      dom_pseudo_bytes(3).

       Note

	       Under Cygwin, the $more_entropy must be set to TRUE for this function to work.

PHP Documentation Group 														 UNIQID(3)