to get RI definitions and all others (views, indexes, etc) execute command db2look (see documentation for detail).
Backup/restore can be done only within Unix platform (AIX, HP, Solaris) and not over different operating system like Unix/Linux (although they seem to be quite the same they are not).
When migrating from one platform to another I do this way:
1. execute db2look to get table, view, foreign keys, indexes, trigger, etc info
2. the output DDL file generated by db2look I split manually into two parts - first part where create tables etc are and into second where create foreign keys are - this is useful you can import tables without needing to have exact relation dependency
3. db2more export ... -> export data from source db
4. connect to target db and execute first part of db2look commands
5. db2move import -> import data into target db
6. execute second part of db2look commands