The following piece of code will update a field of a specific content type by SQL and it is written in a custom module with hook_cron(). Since it updates the database table directly so you have to use it with extreme caution.
function <MODULE>_cron() {
// Get the list of node ids
$sql = "SELECT nid FROM {node} WHERE type = :type";
$result = db_query($sql, array(':type' => '<TYPE>'));
$nids = array();
foreach ($result as $row) {
$nids[] = $row->nid;
}
// Update the table directly
db_update('<FIELD TABLE NAME>')
->fields(array('<FIELD NAME>' => '<NEW VALUE>'))
->condition('entity_id', $nids)
->execute();
// Clear the cache
drupal_flush_all_caches();
}
Done =)
Eureka! 
Hello,
thanks for ths solution.
How can I set the fields value ( fields(array(” => ”)) ) on “today” when it’s a date field?
Best regards
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That depends on the format you have set on your datetime field. Here is an example:
$date = new DateTime() // Get current datetime // For datetime $node->field_datetest[$node->language][0]['value'] = $date->format('Y-m-d H:i:s'); // 2015-01-16 09:21:32 // For date $node->field_datetest[$node->language][0]['value'] = $date->format('Y-m-d\TH:i:s'); // 2015-01-16T09:21:32 // For datestamp $node->field_datetest[$node->language][0]['value'] = strtotime($date->format('Y-m-d H:i:s'));I haven’t tried that, to play safe, please check the corresponsding value stored in the database and make a backup whenever it is needed.
Reference: Programmatically set date fields in Drupal 7: Date, Date (ISO Format) and Date (Unix Timestamp)
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