Running application binaries

An application binary is processed differently depending upon whether it is executed from UNIX or Linux mode, and whether it is a UNIX or Linux binary.

From UNIX mode:

• UNIX binaries process as usual in the UnixWare 7 environment.

• A Linux binary begins running in UNIX mode, but when it makes its first Linux system call it changes root (see chroot(2)) to the /linux directory and continues executing. Typically, an application makes its first system call early in its run, so there is minimal performance impact.

The result of changing root into /linux is that, for a Linux binary, the /linux portion of the UnixWare 7 filesystem is the apparent root. The advantages to this approach are:

• No filename mapping is required.

• A Linux application cannot inadvertently damage UnixWare 7 files.

• If the user or application has changed root to /linux, UnixWare 7 libraries cannot be accidentally overwritten.

• File paths used by Linux applications are all interpreted relative to the new root directory, so Linux commands and syntax work properly.

• Symbolic links created by rpm or other installed packages are automatically interpreted correctly. If absolute, they are interpreted relative to the new root directory.

From Linux mode, the binary first changes root to UnixWare 7, then:

• If it is a UnixWare 7 binary, it processes normally in UNIX mode.

• If it is a Linux binary, it changes root back to the /linux directory when it makes its first Linux system call, then continues executing in Linux mode.