Editing User identifier (section)

===Saved user ID===
The saved user ID is used when a program running with elevated privileges needs to do some unprivileged work temporarily; changing <code>euid</code> from a privileged value (typically <code>0</code>) to some unprivileged value (anything other than the privileged value) causes the privileged value to be stored in <code>suid</code>. Later, a program's <code>euid</code> can be set back to the value stored in <code>suid</code>, so that elevated privileges can be restored; an unprivileged process may set its <code>euid</code> to one of only three values: the value of <code>ruid</code>, the value of <code>suid</code>, or the value of <code>euid</code>.