system users does not exist

[anupama 2004]

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sir/madam
Hi
in my system i have installed fedora core-3
and i dont know why  some system users are deleted  from /etc/passwd
file  and when i start some services like postgresql  , sendmail  etc
the system says system user "postgres"   does't exist
i have some important data in my system. so pls tell me hoew to include
these system users again without reinstalling the packages.
 i tried with forcebly updating the rpms.  but didn't solved the problem

Thanks/Regards
Mallikarjun Mudumali
9880023898
Thanks/Regards
Mallikarjun Mudumali
9880023898