Question about MySQL replica

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http://www.linuxquestions.org – I had a MySQL Master-Slave configuration. The master had a physical failure, and it has been shut down for several days. In the meantime I changed ip of slave server with the master, and I used the command "stop slave". Now the master has been repaired, my doubt is: it's better to move the original master configuration (my.cnf) to slave, in order to make slave the new master? Or should I export all databases from the slave to the master? (HowTos)