erro: can't create transaction lock install .rpm

[Rildo]

HI, I am so Brazil 
 
what does it mean when I do
#rpm -ivh sendmail-devel.rpm, it turns backs 
with message " aviso: sendmail-devel-8.13.1-2.i386.rpm: V3 DSA
signature: NOKEY, key ID 4f2a6fd2
erro: can't create transaction lock "
 
i need to help for problem.   
 
thank you

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