By default, Alfresco uses credential cookies which are valid for only 60 minutes. This means that users may need to log in a few times during the day.
To increase the timeout, edit files /opt/alfresco-4.2.b/tomcat/webapps/share/WEB-INF/web.xml and /opt/alfresco-4.2.b/tomcat/webapps/alfresco/WEB-INF/web.xml:
<session-config>
<session-timeout>1440</session-timeout><!-- 1 day -->
</session-config>
And restart Alfresco.
Increasing the value further is normally useless because the cookies sent by Alfresco (or actually Tomcat) are session cookies. These kind of cookies will be deleted when the user closes his browser.
