When a user runs a Rational ClearCase client utility, such as cleartool or a
GUI program, that utility attempts to obtain a license. If it gets one, the
user can keep the license for an extended period. Entering any Rational
ClearCase command renews the license. If the user does not enter a Rational
ClearCase command for a substantial period—by default, 60 minutes—another
user can take the license.

简单的说：当你开始使用ct时，就会获得一个license，但是这个license是有时间限制的，默认是60秒；只要你在这60秒内什么都没有做，你的license就有可能被分配给别人，反过来只要你使用了，这60秒的限制就会被重新设置陈60秒，重新开始计时。

以下是获取license的步骤：

Whenever a user runs a Rational ClearCase command or GUI, a license-
verification check is made. If the user already has a license, the check
succeeds and the command or GUI runs. If the user does not have a license, the
following steps occur:

1. The Rational ClearCase client software looks for the name of the license
server host.

2. The command or GUI communicates with the license server process on the
license server host, to see whether the user can get a license. (The license
server process is actually the albd_server, performing these duties in
addition to its other tasks.)

3. If a license is available, the license server grants the user a license
and the command or GUI runs.

4. If no license is available, the license server returns a message to that
effect and the command or GUI exits with an error message.