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With this list, we can import our selections back into the server if we need to reinstall 
Ubuntu Server, or into a new server that will serve a similar purpose. First, before we 
manage any packages, we should update our index:
sudo apt update
Next, we'll need to ensure we have the 
dselect
 package installed. The 
dselect
 
package provides us with additional features when managing Debian packages. Its 
finer points are beyond the scope of this chapter, but specific to our current goal, 
we can use it to restore packages from our exported list. At your shell prompt, type 
which dselect
 and you should see output similar to the following:
/usr/bin/dselect
If you don't see the output, you'll need to install the 
dselect
 package with 
apt
:
sudo apt install dselect
Once that's complete, you can now import your previously saved package list, and 
have the missing packages reinstalled on your server. The following commands will 
complete the process:
sudo dselect update
sudo dpkg --set-selections < packages.list
sudo apt-get dselect-upgrade
Normally, we simply use 
apt
 instead of 
apt-get
 nowadays, but oddly enough, the 
dselect-upgrade
 command only works with 
apt-get
.
After you have run those commands, the packages that are contained in your 
packages list but aren't already installed will be installed once you confirm the 
changes. This method allows you to easily restore the packages previously installed 
on your server, if for some reason you need to rebuild it, as well as setting up a new 
server to be configured in a similar way to an existing one.
Now that we have an understanding of how to export and import a list of installed 
packages, we can also take a look at how to clean up unneeded packages, to ensure 
our server is as free as possible from unnecessary bloat.

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Chapter 3