Baikal: A lightweight CalDAV/CardDAV server

August 22nd, 2014 No comments

Baikal is a lightweight, free and open-source CalDAV and CardDAV server implementation that allows you to synchronize your address book and appointments with multiple clients such as mobile devices or a desktop application like Thunderbird. It lacks a couple of important features for enterprise use cases, such as address book and calendar sharing between multiple users, but it’s very suitable for a small office or home installations. Since it’s very lightweight and only depending on php and mysql, it’s also quite fast and stable.

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Installing kvm on Fedora 20

July 16th, 2014 No comments

Installing kvm on a recent Fedora OS is quite easy. Fedora already ships all the necessary software packages and kernel modules for running a kernel virtualised machine.

0. Prerequisites

Since late 2005 / early 2006 almost every x86 processor is capable of hardware virtualization. To check if your CPU supports Intel’s VT-d or AMD’s Pacifica, which is a requirement for hardware virtualization with kvm, run:

# egrep '(vmx|svm)' --color=always /proc/cpuinfo

To install the necessary software packages, run:

# yum -y install qemu-kvm libvirt virt-install bridge-utils 

1. Bridge configuration

There are a couple of ways to give your virtual machines access to your network. For a reference, have a look at the Networking page of the kvm documentation. The easiest way is to add the virtual NICs of your virtual machines as well as the physical NIC on your server to a common bridge.

Let’s assume, you have the following ethernet configuration file for your first ethernet device

# Generated by parse-kickstart
UUID=a9e7f9b1-245a-42d6-84b3-865120c16dd6
DNS1=192.168.1.1
BOOTPROTO=none
DEVICE=eth0
ONBOOT=yes
IPV6INIT=yes
HWADDR=00:8C:00:AA:8C:B8
TYPE=Ethernet
IPADDR0=192.168.1.254
PREFIX0=24
GATEWAY0=192.168.1.1
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME="System eth0"

Let’s create a new bridge device (br0) and add our ethernet device (eth0) to that bridge. First, create a new file called /etc/sysconfig/network-scripts/ifcfg-br0 with the following content:

DNS1=192.168.1.1
BOOTPROTO=none
DEVICE=br0
ONBOOT=yes
IPV6INIT=no
TYPE=Bridge
IPADDR0=192.168.1.254
PREFIX0=24
GATEWAY=192.168.1.1
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
NM_CONTROLLED=no

Second, we’ll need to alter the configuration file for the ethernet device to add the device to the bridge

DEVICE=eth0
ONBOOT=yes
HWADDR=00:8C:00:AA:8C:B8
BRIDGE=br0
TYPE=Ethernet
NM_CONTROLLED=no

To retrieve the MAC address of your ethernet device (eth0) you can use ip link show:

# ip link show 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 00:8c:00:aa:8c:B8 brd ff:ff:ff:ff:ff:ff

Finally, disable the NetworkManager service, enable the network service and reboot the machine.

# systemctl disable NetworkManager.service
# systemctl enable network.service
# reboot

2. Enable libvirt-daemon

The Fedora packages already have a proper systemd init script, which makes enabling and starting the libvirt-daemon rather easy:

# systemctl enable libvirtd.service 
ln -s '/usr/lib/systemd/system/libvirtd.service' '/etc/systemd/system/multi-user.target.wants/libvirtd.service'
# systemctl start libvirtd.service

You can now go ahead and connect to the libvirt-daemon with a GUI, like virt-manager or install a virtual machine with virt-install.

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List cronjobs for all users

May 30th, 2014 No comments

A handy one-liner to list the crontab entries for every user:

$ for user in $(cut -f1 -d: /etc/passwd); do echo $user; crontab -u $user -l; done

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Instaling ownCloud with nginx and php-fpm

March 14th, 2014 3 comments

Setting up an ownCloud instance is rather straight forward. OwnCloud6 rpm packages for recent Fedora versions (20+) already exist and can be easily installed with yum. Unfortunately, ownCloud’s storage mechanism is rather slow compared to other private cloud solution like Seafile or SparkleShare. However the overall speed can be improved greatly by switching from the most obvious and most popular server choice – an apache server – to nginx, for example.

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Revoking an OpenVPN certificate

March 3rd, 2014 No comments

One of the great advantages of using OpenVPN with RSA keys instaed of static keys is the fact that you can easily disable access to the server for a specific client without the need to re-create keys for any other client. This is called revoking of client certificates.

Since every single client’s certificate is verified against a Certificate Revoking List (CRL), disabling a certificate is rather easy. We simply have to create a CRL file and tell OpenVPN to use it. Any match against the CRL will then result in the connection being dropped.

Create a CRL file

The simplest way of dealing with RSA key management in general is probably easy-rsa. You probably set up your OpenVPN server with the help of easy-rsa in the first place, so creating the CRL file is as simple as

# cd /usr/share/easy-rsa/2.0/
# source ./vars 
NOTE: If you run ./clean-all, I will be doing a rm -rf on /usr/share/easy-rsa/2.0/keys
# ./revoke-full client
Using configuration from /usr/share/easy-rsa/2.0/openssl-1.0.0.cnf
Revoking Certificate 04.
Data Base Updated
Using configuration from /usr/share/easy-rsa/2.0/openssl-1.0.0.cnf
client.crt: C = US, ST = CA, L = City, O = name, OU = name.example.org, CN = client, name = client, emailAddress = openvpn@example.org
error 23 at 0 depth lookup:certificate revoked

As you can see in the last line, the certificate was successfully revoke (hence the verification error 23).

You can also see the revoked status of the client’s certificate in the keys/index.txt file. An “R” in the first column indicates, that the certificate was revoked.

[...]
R       240209140518Z   140211140526Z   04      unknown /C=US/ST=CA/L=City/O=name/OU=name.example.org/CN=client/name=client/emailAddress=openvpn@example.org

To examine the newly created CRL file, use

# openssl crl -in keys/crl.pem -text

Configure OpenVPN to use a CRL

Next, we need to tell OpenVPN to verify incoming connections against against our CRL. Copy the crl.pem file to the OpenVPN config directory and assure, that’s it’s readable to the user running the OpenVPN service (usually openvpn:openvpn).

# cp -a keys/crl.pem /etc/openvpn/keys/
# chmod 755 /etc/openvpn/keys/

To tell the OpenVPN server to use a CRL, add the following line to your server’s config file:

[...]
crl-verify keys/crl.pem

After restarting the OpenVPN server, every connection from a client with a revoked certificate should be denied

# journalctl -f
[...]
Feb 11 15:27:05 OpenVPN openvpn[493]: 192.168.8.35:51960 CRL CHECK FAILED: C=US, ST=CA, L=City, O=name, OU=name.example.org, CN=client, name=client, emailAddress=openvpn@example.org is REVOKED
[...]

Resources:
http://blog.remibergsma.com/2013/02/27/improving-openvpn-security-by-revoking-unneeded-certificates/
See also OpenVPN 2.3 manpage

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How to set up a basic OpenVPN bridging server

February 16th, 2014 1 comment

Beside the official OpenVPN documentation there’s a vast number of howtos and guides out there, that’ll tell you how to set up an OpenVPN server. Unfortunately, most of these use a tunneling setup including some sort of router and packet filter. If you want to transport non-IP based traffic and can accept the increased broadcast overhead and poor scalability, you need to setup an OpenVPN bridge.

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sshuttle error: File “ssubprocess.py”, line 1117, in _execute_child

February 1st, 2014 1 comment

If you run into this error:

# sshuttle -r user@remotehost -v 192.168.0.0/24
Starting sshuttle proxy.
Listening on ('127.0.0.1', 12300).
firewall manager ready.
c : connecting to server...
user@remotehost's password: 
 s: latency control setting = True
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "assembler.py", line 26, in <module>
  File "server.py", line 168, in main
  File "server.py", line 68, in list_routes
  File "server.py", line 47, in _list_routes
  File "ssubprocess.py", line 606, in __init__
  File "ssubprocess.py", line 1117, in _execute_child
OSError: [Errno 2] No such file or directory
c : fatal: server died with error code 1

the culprit is simply the missing netstat program on the target host. sshuttle tries to fork a netstat process without checking if netstat is installed on the target host in the first place.

On a Fedora host netstat comes with the net-tools package:

yum install net-tools

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Installing OpenERP 7.0 on Fedora 20

January 22nd, 2014 1 comment

OpenERP is a free an open-source enterprise resource planning (ERP) software. It’s written in Python and makes heavy use of JavaScript and XML and runs completely in that runs in your browser.

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Installing OpenProject 3.0 on Fedora 20

January 6th, 2014 4 comments

OpenProject is an open source project management software. It’s a web-based system that runs in your browser and is built on Ruby on Rails. What makes it really worth-wile is a wide set of features and plugins and a very active and always helpful community.
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Convert pdf to dxf

December 16th, 2013 No comments

To quickly convert a pdf file to dxf, there’s a neat little tool called pstoedit. It’s part of Fedora’s standard repository and can be installed via yum

# yum install pstoedit

To convert a file named Drawing.pdf run:

$ pstoedit -f "dxf: -ctl -mm" Drawing.pdf Drawing%d.dxf

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