Vsftpd is the most easy ftp server to setup.
The configuration file for vsftpd is located in /etc/vsftpd.conf. The default configuration is a little bit paranoid, not so usable for file sharing. So use this configuration instead:
sudo apt-get install vsftpd
Don't forget to backup before you use this configuration.
# Put in /etc/vsftpd.conf
# Don't forget to change samurai into your local username
ftpd_banner=Welcome to blah FTP service.
Now we must make writable directory for anonymous user.
sudo cp /etc/vsftpd.conf /root/
Ok, I explain this. In my local system, I have user named 'samurai'. With this configuration, I can log into ftp server with local user, that is 'samurai'. 'samurai' can go anywhere, create files, delete files, etc as long as he has sufficient permission.
sudo mkdir opendir
sudo chmod 777 opendir/
With this configuration I can log into ftp server with anonymous user ( without username and password ). After logging in, the anonymous user jailed in /home/ftp directory ( pointed by anon_root ). I can't go outside. I can download files from /home/ftp directory but not create, delete anything from this directory. But I can write and delete files in opendir. If I write files in opendir or upload files in opendir, the files automatically belong to 'samurai' user.
To run this server:
To stop it:
sudo /etc/init.d/vsftpd start
To restart it:
sudo /etc/init.d/vsftpd stop
Now it is usable for file sharing, right?!!!!
sudo /etc/init.d/vsftpd restart