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diff --git a/docs/dependencies b/docs/dependencies new file mode 100644 index 000000000..6973bec51 --- /dev/null +++ b/docs/dependencies @@ -0,0 +1,110 @@ +DEPENDENCIES +============ + +Dependencies provide a way for a package builder to require other +packages or capabilities to be installed before or simultaneously +with one another. These can be used to require a python interpretor +for a python based application for example. RPM ensures dependencies +are satisfied whenever packages are installed, erased, or upgraded. + +Requiring Packages +------------------ + +To require packages, use: + + Requires: python perl + +in the spec file. Note that "Requires python, perl" would work as well. If you +needed to have a very recent version of python but any version of perl, + + Requires: python >= 1.3, perl + +would do the trick. Again, the ',' in the line is optional. Instead of +'>=', you may also use '<', '>', '<=', or '='. + +RPM uses an internal algorithm to determine version number orderings which +works correctly most of the time. For example, it will know that +1.9a is older then 1.9b. However, it will also be later then 1.9 which +may or may not be correct as some programmers use letters in version numbers +to indicate beta versions. + +To work around this, you may specify a serial number for a package like this: + + Serial: 23 + +If a Requires: line should be comparing the given number with a serial number +instead of a version number, you would do this: + + Requires: somepackage =S 23 + +Virtual Packages +---------------- + +Sometimes you need to make sure the system your package is being installed +on has a package which provides a certain capability, even though you don't +care what specific package provides it. For example, sendmail won't work +properly unless a local delivery agent (lda) is present. You can ensure that +one is installed like this: + + Requires: lda + +This will match either a package called lda (as mentioned above), or any +package which contains: + + Provides: lda + +in its .spec file. No version numbers may be used with virtual packages. + +Automatic Dependencies +---------------------- + +To reduct the amount of work required by the package builder, RPM scans +the file list of a package when it is being built. Any files in the file +list which require shared libraries to work (as determined by ldd) cause +that package to require the shared library. + +For example, if your package contains /bin/vi, RPM will add dependencies +for both libtermcap.so.2 and libc.so.5. These are treated as virtual +packages, so no version numbers are used. + +A similar process allows RPM to add Provides information automatically. Any +shared library in the file list is examined for its soname (the part of +the name which must match for two shared libraries to be considered +equivalent) and that soname is automatically provided by the package. For +example, the libc-5.3.12 package has provides information added for +libm.so.5 and libc.so.5. We expect this automatic dependency generation +to eliminate the need for most packages to use explicit Requires: lines. + +Installing and Erasing Packages with Dependencies +------------------------------------------------- + +For the most part, dependencies should be transparent to the user. However, +a few things will change. + +First, when packages are added or upgraded, all of their dependencies +must be satisfied. If they are not, an error message like this appears: + + failed dependencies: + libICE.so.6 is needed by somepackage-2.11-1 + libSM.so.6 is needed by somepackage-2.11-1 + libc.so.5 is needed by somepackage-2.11-1 + +Similarly, when packages are removed, a check is made to ensure that +no installed packages will have their dependency conditions break due to +the packages being removed. If you wish to turn off dependency checking for +a particular command, use the --nodeps flag. + +Querying with Dependencies +-------------------------- + +Two new query information selection options are now available. The first, +--provides, prints a list of all of the capabilities a package provides. +The second, --requires, shows the other packages that a package requires +to be installed, along with any version number checking. + +There are also two new ways to search for packages. Running a query with +--whatrequires <item> queries all of the packages that require <item>. +Similarly, running --whatprovides <item> queries all of the packages that +provide the <item> virtual package. Note that querying for package that +provides "python" will not return anything, as python is a package, not +a virtual package. |