TimeCapsule is the Apple (closed) backup system. But... even if closed, you can configure a linux server to be your TimeMachine network disk, like TimeCapsule does.

First of all you need a linux system and, to follow this step-by-step guide, you need a CentOS 6.X linux.

Installation

Configure EPEL repository, if your system is not yet configured with it:

Bash

sudo rpm -Uvh http://www.mirrorservice.org/sites/dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm

Then install all the necessary services:

Bash

sudo yum clean allsudo yum make cachesudo yum -y install netatalk avahi  dbus nss-mdns

Configuration

Configure netatalk service editing the /etc/netatalk/afpd.conf file and adding the following line at the end of the file:

Bash

- -transall -uamlist uams_randnum.so,uams_dhx.so,uams_dhx2.so -nosavepassword -advertise_ssh

Create folder to use for TimeMachine backups:

Bash

mkdir -p /mnt/data/TimeMachinechown youruser:youruser /mnt/data/TimeMachine

Where youruser is a linux local user that can connect to the system (with a password) and the one you want to allow to use TimeMachine backup.

Then edit the netatalk AppleVolumes file (/etc/netatalk/AppleVolumes.default) and add the folder you want to use for your backups:

Bash

/mnt/data/TimeMachine allow:youruser options:usedots,upriv,tm dperm:0775 fperm:0660 cnidscheme:dbd

You just need to change youruser with the previously selected user.

Next configure the nsswitch service into the file /etc/nsswitch.conf and add the following line at the end:

Bash

hosts:      files mdns4_minimal dns mdns mdns4

In Avahi, configure the afpd service to be brodcasted on the network via the avahi daemon. Create the file /etc/avahi/services/afpd.service with the following content:

XML

<?xml version=”1.0″ standalone=’no’?><!DOCTYPE service-group SYSTEM “avahi-service.dtd”><service-group><name replace-wildcards=”yes”>%h</name><service><type>_afpovertcp._tcp</type><port>548</port></service><service><type>_device-info._tcp</type><port>0</port><txt-record>model=TimeCapsule</txt-record></service></service-group>

Disable the SSH service from avahi:

Bash

mv /etc/avahi/services/ssh.service /etc/avahi/services/ssh.service.disabled

If you have iptables enabled on your system, you need to open the ports used by TimeMachine. Add these lines to your /etc/sysconfig/iptables file:

Bash

-A INPUT -p tcp -m state --state NEW -m tcp --dport 548 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 5353 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 5354 -j ACCEPT
-A INPUT -p udp -m udp --dport 548 -j ACCEPT
-A INPUT -p udp -m udp --dport 5353 -j ACCEPT
-A INPUT -p udp -m udp --dport 5354 -j ACCEPT

Reload the iptables configuration, or restart the service:

Bash

/sbin/service iptables restart

Ensable and start all service:

Bash

/sbin/chkconfig netatalk on
/sbin/chkconfig messagebus on
/sbin/chkconfig avahi-daemon on

/sbin/service avahi-daemon restart
/sbin/service messagebus restart
/sbin/service netatalk restart

Going back to your Mac the disk should be visible in your TimeMachine. 
If not try to check services (/sbin/service xxx status) and restart them.

Enjoy your new OpenSource (and low cost!!) TimeCapsule

From: https://blog.mornati.net/centos-6-as-apple-timemachine-backup/