Ubuntu - Debian Package Management

rpm - dpkg equivalents

rpm -qa becomes dpkg -l
rpm -qf becomes dpkg -S
rpm -qal becomes for i in `dpkg-query -W|awk '{print $1}'`; do dpkg -L $i; done

SSH delays

Sometimes when I login I get very long delay,
cause is the destination server's config, two possible configs:
/etc/ssh/sshd_config in Centos, /etc/sshd_config under OSX:

UseDNS no
- and/or -
GSSAPIAuthentication no

LCD Monitor DPI at Native Resolution

Relative pixel density for a given resolution
calculated this way:
DPI = sqrt( Wpx^2+Hpx^2 )

1680x1050@20" --> 99dpi
1600x1200@21" --> 95dpi
1680x1050@22" --> 90dpi
1920x1200@24" --> 94dpi

using google as my calculator (e.x. for 1920x1200#24")