dpkg: unrecoverable fatal error, aborting: unknown user 'postfix' in statoverride file E: Sub-process /usr/bin/dpkg returned an error code (2)的修复

grep 'postfix' /var/lib/dpkg/statoverride

sed -i '/postfix/d' /var/lib/dpkg/statoverride 

即可修复。

参考http://rickfoosusa.blogspot.co.il/2012/04/howto-ubuntu-unknown-user-in.html