Instalando o proftpd
Instalação:
# apt-get install proftpd
Adicione o seguinte no arquivo 
/etc/shells:
/bin/false
Crie o diretório para o serviço, pode ser o padrão /home/ftp ou outro qualquer.
# mkdir /var/ftp
Permissões (levando em conta que é uma pasta para download e upload):
# chmod 777 /var/ftp
Adicionar usuário:
    
No lugar de /var/ftp coloque o caminho da pasta criada anteriormente.
# useradd USUARIO -p SENHA -d /var/ftp -s /bin/false
 
Se houver algum problema com a autenticação do usuário, use o comando passwd e redigite a senha.
# passwd USUARIO
A seguir, vamos configurar o proftpd.conf.
Configurando o proftpd.conf
O arquivo de configuração do FTP está em 
/etc/proftpd/proftpd.conf.
 
Abaixo está o arquivo padrão, as alterações básicas necessárias estão destacadas. Dependendo de cada caso pode ser necessário alterar mais algum detalhe. No geral, é só copiar o texto abaixo e salvá-lo na mesma pasta e com as mesmas permissões do arquivo original.
Por segurança, pode-se salvar o arquivo original como proftpd.conf.bkp. Assim, se no futuro for preciso, o arquivo ainda estará a disposição.
#
# /etc/proftpd/proftpd.conf -- This is a basic ProFTPD configuration file.
# To really apply changes reload proftpd after modifications.
# 
# Includes DSO modules
Include /etc/proftpd/modules.conf
# Set off to disable IPv6 support which is annoying on IPv4 only boxes.
UseIPv6                         on
# If set on you can experience a longer connection delay in many cases.
IdentLookups                    off
### Nome do servidor - pode ser qualquer nome
ServerName                      "meu-ftp"
ServerType                      standalone
DeferWelcome                    on
MultilineRFC2228                on
DefaultServer                   on
ShowSymlinks                    off
TimeoutNoTransfer               600
TimeoutStalled                  600
TimeoutIdle                     1200
DisplayLogin                    welcome.msg
DisplayChdir                    .message true
ListOptions                     "-l"
DenyFilter                      \*.*/
### Nome da pasta criada para o serviço, no caso /var/ftp
 DefaultRoot                    /var/ftp
### Não permitir que os usuarios saiam da sua pasta home
#(isso é muito importante, do contrário os usuários poderão ter
#acesso a outras pastas do sistema, o que não seria nada bom.
 DefaultRoot                    ~
# Users require a valid shell listed in /etc/shells to login.
# Use this directive to release that constrain.
# RequireValidShell             off
### A porta 21 é a padrão mas pode usar outra, no entanto é preciso especificar o numero
#da porta ao digitar o endereço (ex: ftp://ip:porta)
Port                            1980
# In some cases you have to specify passive ports range to by-pass
# firewall limitations. Ephemeral ports can be used for that, but
# feel free to use a more narrow range.
# PassivePorts                  49152 65534
# If your host was NATted, this option is useful in order to
# allow passive tranfers to work. You have to use your public
# address and opening the passive ports used on your firewall as well.
# MasqueradeAddress             1.2.3.4
# This is useful for masquerading address with dynamic IPs:
# refresh any configured MasqueradeAddress directives every 8 hours
<IfModule mod_dynmasq.c>
# DynMasqRefresh 28800
</IfModule>
# To prevent DoS attacks, set the maximum number of child processes
# to 30.  If you need to allow more than 30 concurrent connections
# at once, simply increase this value.  Note that this ONLY works
# in standalone mode, in inetd mode you should use an inetd server
# that allows you to limit maximum number of processes per service
# (such as xinetd)
MaxInstances                    30
# Set the user and group that the server normally runs at.
User                            proftpd
Group                           nogroup
# Umask 022 is a good standard umask to prevent new files and dirs
# (second parm) from being group and world writable.
Umask                           022  022
# Normally, we want files to be overwriteable.
AllowOverwrite                  on
# Uncomment this if you are using NIS or LDAP via NSS to retrieve passwords:
# PersistentPasswd              off
# This is required to use both PAM-based authentication and local passwords
# AuthOrder                     mod_auth_pam.c* mod_auth_unix.c
# Be warned: use of this directive impacts CPU average load!
# Uncomment this if you like to see progress and transfer rate with ftpwho
# in downloads. That is not needed for uploads rates.
#
# UseSendFile                   off
TransferLog /var/log/proftpd/xferlog
SystemLog   /var/log/proftpd/proftpd.log
<IfModule mod_quotatab.c>
QuotaEngine off
</IfModule>
<IfModule mod_ratio.c>
Ratios off
</IfModule>
# Delay engine reduces impact of the so-called Timing Attack described in
# http://security.lss.hr/index.php?page=details&ID=LSS-2004-10-02
# It is on by default. 
<IfModule mod_delay.c>
DelayEngine on
</IfModule>
<IfModule mod_ctrls.c>
ControlsEngine        off
ControlsMaxClients    2
ControlsLog           /var/log/proftpd/controls.log
ControlsInterval      5
ControlsSocket        /var/run/proftpd/proftpd.sock
</IfModule>
<IfModule mod_ctrls_admin.c>
AdminControlsEngine off
</IfModule>
#
# Alternative authentication frameworks
#
#Include /etc/proftpd/ldap.conf
#Include /etc/proftpd/sql.conf
#
# This is used for FTPS connections
#
#Include /etc/proftpd/tls.conf
# A basic anonymous configuration, no upload directories.
# <Anonymous ~ftp>
#   User                                ftp
#   Group                               nogroup
#   # We want clients to be able to login with "anonymous" as well as "ftp"
#   UserAlias                   anonymous ftp
#   # Cosmetic changes, all files belongs to ftp user
#   DirFakeUser on ftp
#   DirFakeGroup on ftp
# 
#   RequireValidShell           off
# 
#   # Limit the maximum number of anonymous logins
#   MaxClients                  10
# 
#   # We want 'welcome.msg' displayed at login, and '.message' displayed
#   # in each newly chdired directory.
#   DisplayLogin                        welcome.msg
#   DisplayChdir                .message
# 
#   # Limit WRITE everywhere in the anonymous chroot
#   <Directory *>
#     <Limit WRITE>
#       DenyAll
#     </Limit>
#   </Directory>
# 
#   # Uncomment this if you're brave.
#   # <Directory incoming>
#   #   # Umask 022 is a good standard umask to prevent new files and dirs
#   #   # (second parm) from being group and world writable.
#   #   Umask                           022  022
#   #            <Limit READ WRITE>
#   #            DenyAll
#   #            </Limit>
#   #            <Limit STOR>
#   #            AllowAll
#   #            </Limit>
#   # </Directory>
# 
# </Anonymous>