Installed Images

Certain images can be installed. This does not refer to software installation, where new programs are loaded from a distribution medium. An installed image, also called a known file, is a file registered via the DCL INSTALL command to have special attributes.

Installed images may be assigned elevated privileges, temporarily granting those privileges to any user who executes the image. An example is the OpenVMS MAIL facility. To send mail to another local user, a file in that user's login directory must be modified, something that other users are not normally permitted to do.

To allow this special circumstance, the MAIL program is installed with the privileges necessary to write files in someone else's directory. Any user running the MAIL program is granted those privileges only while the MAIL program is executing. When the MAIL program exits, the user's privileges are returned to normal.

Note 

Because of their sensitive nature, installed images do not include support for the debugger, image dump, or traceback facilities.

Installed images may also be used to conserve system resources. They may be specified as permanently open and have their image headers resident in memory at all times. When frequently used images are installed in this manner, their startup time is significantly reduced. Many of the OpenVMS operating system images are installed this way.