In the following we use the term **architecture qualified package name**
(or *arch-qualified package names* for short) to refer to package
-identifiers of the form "arch:package" where "arch" is a dpkg
-architecture and "package" a dpkg package name.
+identifiers of the form "package:arch" where "package" is a package name
+and "arch" a dpkg architecture.
## Components
- **Dir::Bin::Solvers**: absolute path of the directory where to look for
external solvers. Defaults to `/usr/lib/apt/solvers`.
+
## Protocol
When configured to use an external solver, APT will resort to it to
- **APT-Candidate:** (optional, defaults to `no`). Allowed values:
`yes`, `no`. When set to `yes`, the corresponding package is the APT
candidate for installation among all available packages with the same
- name and with the same architecture.
+ name and architecture.
- **APT-Automatic:** (optional, defaults to `no`). Allowed values:
`yes`, `no`. When set to `yes`, the corresponding package is marked by
Release file entry (Origin, Label, Codename, etc.) in the format of
APT_PREFERENCES(5).
+
### Answer
An answer from the external solver to APT is either a *solution* or an
The following invariant on **exit codes** must hold true. When the
external solver is *able to find a solution*, it will write the solution
to standard output and then exit with an exit code of 0. When the
-external solver is *unable to find a solution* (and s aware of that), it
-will write an error to standard output and then exit with an exit code
-of 0. An exit code other than 0 will be interpreted as a solver crash
-with no meaningful error about dependency resolution to convey to the
-user.
+external solver is *unable to find a solution* (and is aware of that),
+it will write an error to standard output and then exit with an exit
+code of 0. An exit code other than 0 will be interpreted as a solver
+crash with no meaningful error about dependency resolution to convey to
+the user.
#### Solution