Since you've only deleted
/usr/lib/* and not
/lib/*, you can probably recover. I think all the programs you critically need to recover your system only use libraries from
Boot to a text login prompt. If the normal boot doesn't give you a
login: prompt in text mode, boot with only minimum services. Press and hold Shift when your computer starts to show the Grub prompt; you need to press the key after the BIOS has initialized the keyboard but before Grub is loaded, which on some machines leaves only a small time window and may require several attemps. At the Grub prompt, press Down to highlight the single-user mode boot entry and boot that.
Once you have a command line, run
apt-get --reinstall install PACKAGE1 PACKAGE2 … to reinstall the packages that have files in
/usr/lib. You can run this shell snippet to get the list of names of packages to reinstall:
egrep -l '/usr/lib/[^/]*\.so\.' /var/lib/dpkg/info/a*.list |
sed -e 's!^/var/lib/dpkg/info/!!' -e 's!\.list$!!'
Some package installation scripts may require libraries from other packages to be present, so you may need to run the reinstallations in a particular order. If you find that a package's installation scripts are trying to use a particular program, you can find out which libraries this program needs with
ldd. For example, this indicates that python is missing three libraries that you need to reinstall:
$ ldd /usr/bin/python | grep 'not found'
libssl.so.0.9.8 => not found
libcrypto.so.0.9.8 => not found
libz.so.1 => not found
dpkg -S /usr/lib/libz.so.1 reveals that this file comes from
zlib1g, and so on.
If you find that
apt-get is unable to download packages, first download a few key packages from a live CD.
libssl0.9.8 are two packages you're very likely to need early on.