On Gentoo Linux, package dependencies are managed using Ebuild variables. These variables define when and how dependencies are required during different phases of package installation. Here’s what each of them means:

1. DEPEND (Build-time dependencies)

   • Specifies dependencies required at build time.
   • These are necessary only while compiling the package.
   • Once the package is installed, these dependencies may no longer be needed.

2. RDEPEND (Run-time dependencies)

   • Specifies dependencies required at runtime.
   • These are needed for the package to function properly after installation.
   • Usually, RDEPEND and DEPEND are the same unless the package needs something only during compilation.

3. BDEPEND (Build-time dependencies for binary packages)

   • Specifies build dependencies needed when cross-compiling or using a binary package.
   • Useful for bootstrapping or when building packages in an isolated environment.
   • Use Case: When cross-compiling, BDEPEND ensures that necessary tools (like gcc) are available in the build environment.

4. IDEPEND (Install-time dependencies)

   • Specifies dependencies needed only during package installation.
   • Once the package is installed, these dependencies can be removed.
   • Use Case: If a package needs unzip only to extract files during installation.

5. PDEPEND (Post-install dependencies)

   • Specifies dependencies that must be installed after the package is installed.
   • Used when a package cannot be installed until another package is fully set up.
   • Use Case: If a package installs correctly without dbus, but it needs dbus to function properly later.