Which directory in Linux contains installed software, shared libraries, include files, and read-only program data?

The directory that contains installed software, shared libraries, include files, and read-only program data is /usr. This directory is fundamental in a Linux system as it houses the majority of user utilities and applications.

Within /usr, you can find subdirectories like /usr/bin—which contains executable programs for user commands—and /usr/lib—which holds shared libraries used by those programs. This structure helps maintain organization and ensures that user applications and their resources are stored separately from system files.

In contrast, /opt is typically used for optional software packages that are not part of the standard distribution, while /bin contains essential user command binaries needed for system operation, and /lib holds essential shared libraries required by the binaries in /bin and /sbin. Thus, /usr serves as the primary repository for user-level applications and their associated components, making it the correct choice in this context.