All posts by nicholas

CLI, Mobile, Networking

Use a freedompop phone for OOB management

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I’ve been wanting to have an out of band (OOB) way to manage my home servers for some time now. Why OOB? Sometimes the regular band fails you, like when the internet connection goes down or when I remote into my firewall and fat finger a setting causing the WAN link to go down. Everything is still up, I just can’t get to it remotely. I then have to drive home to fix it all like a luser. This is especially difficult if I’m out of town.

Enter Freedompop. Freedompop is as Sprint MVNO that offers data-only 4g access for cheap – in this case, completely free if you stay under 500 MB of data a month. I got a freedompop phone so my wife could play Ingress before the iOS client came out. Once the iOS Ingress client was released, the freedompop phone began collecting dust.

Note that this would all be a lot simpler if I just did things the “proper” way, such as purchasing a freedompop access point or paying for a tethering plan.. but what’s the fun in that? My solution is quite convoluted and silly – it uses all three types of SSH tunnels –  but it works.. and it was fun!

Hardware

  • Local, out of band server: An old laptop with a broken screen running Xubuntu 14.04
    • Ethernet cable attached to my local network
  • Remote, regularly banded SSH server: My parents’ dd-wrt powered router (any remote ssh server you have access to will do.)
  • Phone: Sprint Samsung Galaxy S3 activated on the Freedompop network
    • Attached to the out of band server via USB

Software

  • openssh-server: Install this on your out of band server so you can SSH into it
    • ssh-keygen: used to generate RSA private/public key pair to allow for passwordless SSH logins
  • screen: Allows programs to keep running even if SSH is disconnected (optional)
  • autossh: Monitors the state of your ssh connection and will continually attempt to re-connect if the connection is lost, effectively creating a persistent tunnel.
  • tsocks: Allows you to tunnel all traffic for a specified command through a SOCKS proxy
  • Android SSH Server (I use SSH server by Icecold apps.) This is an SSH server for android devices, no root required.

Procedure

My strategy uses a system of tunnels through the intertubes to accomplish what I want.

  1. Install the OS, openssh-server, autossh, and tsocks on your OOB server, then disconnect it from the internet while keeping it on your local network (I manually configured the IP to not have a default gateway.)
  2. Install an ssh server on your phone
  3. Tether your phone to the computer via USB
  4. Create a dynamic SOCKS proxy tunnel between the OOB server and your phone (Freedompop appears to block internet traffic through USB tethers unless you have a tethering plan, so I had to get creative.)
  5. Configure tsocks on your OOB server to point to the socks proxy established in step 4
  6. Use autossh in conjuction with tsocks to initiate a reverse tunnel between your OOB server and the remote SSH server over the 4G connection from your freedompop phone
  7. (From some other network) SSH into your remote SSH server and create a local tunnel pointing to the remote tunnel created in step 6.
  8. SSH into your locally created tunnel, and… profit?

Adventure, here we come.

Create private / public keys

First, since we’re going to be creating a persistent tunnel, passwordless login is required. We do this by generating an RSA private/public key pair. Create the key pair on your server as per these instructions:

cd ~/.ssh
ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/nicholas/.ssh/id_rsa): oob
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in oob.
Your public key has been saved in oob.pub.

Copy the public key generated (oob.pub in my case) to your phone.

Configure phone SSH server

Create an SSH server on your phone. Configure the user you created to use the public key generated above. Once that’s configured, start the ssh server on the phone, plug the phone into USB cable and plug the other end into server, and activate USB tethering in Android settings.

On the OOB server, find out IP address of tether by issuing the route command. Look for the gateway on the usb0 interface.

route
Destination Gateway Genmask Flags Metric Ref Use Iface
default 192.168.42.129 0.0.0.0 UG 0 0 0 usb0

In my case the gateway IP is 192.168.42.129.

Configure OOB server

Initiate an autossh connection to the usb0 gateway, creating a dynamic (socks) proxy in the process.

autossh 192.168.42.129 -l nicholas -i ~/.ssh/oob -p 34097 -D9999

Argument breakdown:

  • -l  username to log in as
  • -i keyfile to use (passwordless login, optional but recommended)
  • -p port to ssh to. This will be random and told to you by the android ssh server on the phone.
  • -D port for your dynamic (socks) proxy to bind to. This can be anything of your choosing.

The phone <-> OOB server tunnel is now established. This tunnel will be used to provide 4G internet access to your server.

Next, configure tsocks to use our newly created tunnel. The options we want to modify are Local Networks, server, and server_port.

sudo vi /etc/tsocks.conf

local = 192.168.0.0/255.255.0.0
server = 127.0.0.1
server_port = 9999

You can now use the 4G internet if you prepend tsocks in front of the program you want to use the internet.

Update 07/01/2015 I discovered my off site router changes SSH host keys every reboot. This was causing SSH to fail due to host key mismatches. Disable strict SSH host key checking per this post to get around this:

vi ~/.ssh/config

Host *
    StrictHostKeyChecking no

Update 08/04/2015

I found an even better way than the one above to avoid SSH key changing errors. Simply add the following options to your ssh command:

-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null

That takes care of changing ssh keys for good. Thanks to this site for the info.

Establish tunnel with external server

Now that we have 4g internet we can use autossh to call out to an external SSH server (my parent’s router in my case.) This time we will be initiating a reverse tunnel. It will cause the remote server to listen on a specified port and tunnel all traffic on that port through the SSH tunnel to your local server. Note that you will have to copy your public key generated earlier to this remote host as well.

tsocks autossh <remote server IP/DNS> -p <remote port> -l<remote user> -i <remote keyfile> -R5448:localhost:22

The local <-> remote server tunnel is now established. The remote port to listen on (-R argument)  can be anything of your choosing. Remember what port you used for the last step.

Automating connections

Since the SSH connections are interactive I’ve found it easier to run these commands via screen as I outline in this post. To have these tunnels form automatically on startup we will have to make a quick and dirty upstart script as detailed here and further clarified here.

vi /etc/init/tunnel.conf
author "Your name goes here - optional"
description "What your daemon does shortly - optional"

start on started dbus
stop on stopping dbus

# console output # if you want daemon to spit its output to console... ick
# respawn # it will respawn if crashed/killed

script
 screen -dm bash -c "autossh 192.168.42.129 -l nicholas -i /home/nicholas/.ssh/oob -p34097 -D9999"
 sleep 5
 screen -dm bash -c "tsocks autossh dana.jeppson.org -l root -p 443 -i /home/nicholas/.ssh/oob -R5448:localhost:22"
end script

sudo initctl reload-configuration

Accessing your server out of band

Now that we have a tunnel established between our local and remote servers, we can access our local server through the remote server. On the remote server:

ssh localhost -p5448

The -p command of ssh specifies which port to connect to. Since we have a reverse tunnel listening on port 5448, the server will take the ssh connection you’ve initiated and send it through the intertubes to your OOB server over its 4G connection.

If you would rather SSH into your OOB server directly from your laptop instead of through your remote SSH server, you will need to create more tunnels, this time regular local port forwarding tunnels. Why would you possibly want more tunnels? If you want to access things like SSH, VNC or RDP for servers on your network through your OOB tunnel directly to your laptop, it will be necessary to create even more tunnels through the tubes.

First tunnel (to expose the OOB server’s SSH port to your laptop)

ssh <remote server> -L2222:localhost:5448

-L specifies which port your laptop will listen on. The other two parts  specify where your laptop will send traffic it sees on that port (from the perspective of the remote SSH server.)

Second tunnel (to expose ports of servers of your choosing to your laptop as well as give you shell access to your local OOB server) You can add as many -L arguments as you wish, one for each address/port combination you wish to access.

ssh localhost -p2222 -L3333:192.168.1.10:3389 ... ...

Why?

If you’ve made it this far, congratulations. This was an exercise in accessing my home network even if the internet connection goes down. You could bypass half of these tunnels if you set up an openvpn server on your out of band server, but that’s a tutorial for another time.

If you followed this madness you would have the following tunnels through the tubes:

  • SOCKS proxy tunnel from server to phone
  • Remote port forward tunnel from OOB server to remote server
  • Local port forward from remote server to your computer
  • Local port forward(s) from your computer to anything on your local network through the tunnel created above
Analytics

Determine what a Splunk forwarder is forwarding

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I recently came across a need to determine exactly what is logging to a forwarder in Splunk. I had a hard time finding out what to search for so I thought I’d share what I found.

The key to discovering where data is coming in from is in Splunk’s metrics.log files. Searching these files gives us what we need. This search reveals anything coming in over UDP (you can also change it to be TCP if desired) and totals it by host (forwarder.)

source=*metrics.log group=udpin_connections | stats count by host

Oddly enough Splunk doesn’t have a field extracted for its own metrics.log. A key useful field is missing – sourceHost. I used the field extraction tool to create it and it generated this field extraction:

^[^,\n]*,\s+(?P<sourceHost>\d+\.\d+\.\d+\.\d+)

Field extraction in hand, I was able to generate the report I was looking for: devices actively sending logs to my forwarder over UDP.

source=*metrics.log group=udpin_connections  host=splunk | stats count by sourceHost sourcePort

where host is the forwarder you want to investigate. Useful.

OS, Virtualization

Fix Xen VGA Passthrough in Linux Mint 17.1

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I wrote in my last post about how I upgraded from Linux Mint 16 to 17.1. I thought everything went smoothly, but it turns out one feature did break: VGA passthrough via Xen. For the past year or so I’ve had a Windows 8.1 gaming VM with direct access to my video card. It’s worked out nicely in Linux Mint 16 but broke completely in 17.1.

I followed the advice of powerhouse on the Linux Mint forums on how to get things up and running, but it wasn’t quite enough. After much banging of my head against the wall I read on the Xen mailing list that there was a regression in VGA passthrough functionality with Xen 4.4.1, which is the version of Xen Mint 17.1 uses.

I finally came to a solution to my problem today – upgrade to Xen 4.5. I couldn’t find any pre-built packages for Ubuntu 14.04 (the base of Mint 17.1) so I ended up compiling Xen 4.5 from source. Below is what I did to make it all work.

Fix broken symlink for /usr/lib/xen-default

sudo rm /usr/lib/xen-default
sudo ln -s /usr/lib/xen-4.4/ /usr/lib/xen-default

Update the DomU CFG file

A couple things needed tweaking. Here is my working cfg:

builder='hvm'
memory = '8192'
name = 'win8.1'
vcpus=6
cpus="2-7"
pae=1
acpi=1
apic=1
vif = [ 'mac=3a:82:47:2a:51:20,bridge=xenbr0,model=virtio' ]
disk = [ 'phy:/dev/mapper/desktop--xen-Win8.1,xvda,w' ]
device_model_version = 'qemu-xen-traditional'
boot='c'
sdl=0
vnc=1
vncpasswd=''
stdvga=0
serial='pty'
tsc_mode=0
viridian=1
usb=1
usbdevice='tablet'
gfx_passthru=0
pci=[ '01:00.0', '01:00.1' , '00:1d.0' ]
localtime=1
pci_power_mgmt=1
on_xend_stop = "shutdown"
xen_platform_pci=1
pci_power_mgmt=1

For some, that’s all they had to do. For me, I had to do a few more things.

Compile Xen 4.5

This step was thanks to two different sites, this one and this one.

Install necessary packages

sudo apt-get install build-essential bcc bin86 gawk bridge-utils iproute libcurl3 libcurl4-openssl-dev bzip2 module-init-tools transfig tgif texinfo texlive-latex-base texlive-latex-recommended texlive-fonts-extra texlive-fonts-recommended pciutils-dev mercurial libjpeg-dev make gcc libc6-dev-i386 zlib1g-dev python python-dev python-twisted libncurses5-dev patch libvncserver-dev libsdl-dev libpixman-1-dev iasl libbz2-dev e2fslibs-dev git-core uuid-dev ocaml ocaml-findlib libx11-dev bison flex xz-utils libyajl-dev gettext markdown libaio-dev pandoc

Checkout Xen source

git clone git://xenbits.xen.org/xen.git xen-4.5.0
cd xen-4.5.0
git checkout RELEASE-4.5.0

Build from source

./configure --libdir=/usr/lib
 make world -j8

When I tried this the make failed with this error:

/usr/include/linux/errno.h:1:23: fatal error: asm/errno.h: No such file or directory
 #include <asm/errno.h>

The fix (thanks to askubuntu)  was to install linux-libc-dev and make a symlink for it:

sudo apt-get install linux-libc-dev
sudo ln -s /usr/include/asm-generic /usr/include/asm

It then compiled successfully.

Install freshly compiled Xen 4.5

sudo make install
sudo update-rc.d xencommons defaults
sudo update-rc.d xendomains defaults
sudo ldconifg

Set grub to boot from new Xen kernel

sudo update-grub
sudo vim /etc/default/grub

Edit GRUB_DEFAULT to match wherever update-grub put your new Xen kernel (in my case it was the second entry, so my GRUB_DEFAULT=1), then run update-grub again

sudo update-grub

Reboot

Success at last. Enjoy your VM gaming once more with Xen 4.5.

CLI, OS

Upgrade Linux Mint 16 to 17.1

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I realized recently that my desktop system is quite out of date. It has worked so well for so long that I didn’t realize for a while that it was end of support. I was running Linux Mint 16 – Petra.

Thanks to this site the upgrade was fairly painless – a few repository updates, upgrade, and reboot. Simple! The steps I took are below

Update all repositories

Use sed in conjunction with find to quickly and easily update all your repository files from saucy to trusty, and from petra to rebecca, making a backup of files modified.

sudo find /etc/apt/sources.list.d/ -type f -exec sed --in-place=.bak 's/saucy/trusty/' {} \;
sudo find /etc/apt/sources.list.d/ -type f -exec sed --in-place=.bak 's/petra/rebecca/' {} \;

Update your system

This took a while. It had to download 1.5GB of data and install it.

sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get upgrade

Cleanup

After running the upgrade I had a notice that I had many packages that were installed but no longer required. To remove unnecessary packages after the upgrade:

sudo apt-get autoremove

Install new language settings:

sudo apt-get install mintlocale

Install gvfs-backends (for Thunar)

sudo apt-get install gvfs-backends

Reboot

Flawless! It worked on the first try. Awesome.

CLI

Use BASH to append an incremental suffix to directories

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In migrating Splunk indexes I came across the need to add an incrementing suffix of _(numbers) to a bunch of directories. For example, renaming directories

test
test1
test2
test3

to

test_100
test1_101
test2_102
test3_103

After a bunch of searching I settled on this approach of using a simple bash loop to accomplish this:

I=100; for F in db_*; do mv $F $F\_$I; I=$((I+1)); done

There is an initial variable, I, which is set to 100. The for loop goes through each file beginning with db_ and then renames it adding the proper suffix in the iteration (_###). The last step is to increment the value of I.

Replace I for whatever you want you suffix to begin with and change db_* with whatever the criteria for the files you want to rename are. Simple, but it works.

Web

Block annoying bots with Apache .htaccess

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Recently one of my sites has been having its database crash repeatedly. Investigation reveals it always happens while an aggressive bot is crawling it. Since the site is small it was causing the database to run out of memory and die.

The Web Application Firewall that this site is behind frustratingly does not have a feature for blocking user agents. I decided to resort to Apache on the webserver itself to serve as a gatekeeper. The user agent in question? flipboard proxy. It also conveniently appears to ignore robots.txt.

Thanks to this article I learned the details on how to get Apache to block this particular user agent. Creating an .htaccess file (if it doesn’t already exist) and putting it in the root directory of the website causes it to apply to the entire site. Within the .htaccess file, place the following directives:

#block bad bots with a 403
#SetEnvIfNoCase User-Agent "facebookexternalhit" bad_bot
SetEnvIfNoCase User-Agent "Twitterbot" bad_bot
SetEnvIfNoCase User-Agent "Baiduspider" bad_bot
SetEnvIfNoCase User-Agent "MetaURI" bad_bot
SetEnvIfNoCase User-Agent "mediawords" bad_bot
SetEnvIfNoCase User-Agent "FlipboardProxy" bad_bot
<Limit GET POST HEAD>
 Order Allow,Deny
 Allow from all
 Deny from env=bad_bot
</Limit>

Save the file in the root of your website and make sure its permissions are such that your apache server can read the file. Success! Flipboard proxy (and other bad bots) no longer crashes the site. Instead, it gets served a 403 – Forbidden page for every request it makes.

Networking

Configure full VPN tunnel in Sophos UTM

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For years now I have had a successful split tunnel VPN with my Sophos UTM. Recently I’ve wanted to have a full tunnel option for greater security in remote areas (hotel wi-fi, etc.) Unfortunately setting up such a thing in Sophos is NOT straightforward.

The biggest problem I had was that no websites would work after the VPN was initiated. NSlookup was fine, connection was fine, even internal sites would load properly, but no external internet.

Thanks to this post I finally found the culprit: the pesky allowed networks feature for each UTM function. In my case, the VPN was allowing all the necessary traffic through but my transparent proxy was denying web access. I had to add my VPN pool to the list of allowed networks to my proxy.

To summarize, this is what you must do to have a full VPN tunnel:

  • Configure the desired method in the Remote Access section. Take note of whatever IP pool you use for your VPN. In my case I used VPN Pool (SSL)
  • Ensure that internet access is in the list of allowed networks for the user you’ve configured for VPN (Any, or Internet IPv4/6)
  • Add your VPN pool to the list of allowed networks for each service you use.
    • Network services / DNS
    • Web Protection / Web Filtering
  • Profit
OS, Virtualization

Slow Linux VM performance in VMware vSphere

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Recently I’ve been scratching my head over a particular performance issue with Linux VMs hosted on VMWare vSphere. Everything seemed to move at a glacial pace.

vmstat gave a few clues as to what was happening, although depending on what I read it still wasn’t clear:

vmstat

It became apparent that I was suffering from some kind of queuing problem. I wasn’t sure if it was CPU or disk related. I came across this post which has a lot of good performance tuning guides.This tip caught my eye:

 

7. Set your disk scheduling algorithm to ‘noop’

The Linux kernel has different ways to schedule disk I/O, using schedulers like deadline, cfq, and noop. The ‘noop’ — No Op — scheduler does nothing to optimize disk I/O. So why is this a good thing? Because ESX is also doing I/O optimization and queuing! It’s better for a guest OS to just hand over all the I/O requests to the hypervisor to sort out than to try optimizing them itself and potentially defeating the more global optimizations.

You can change the kernel’s disk scheduler at boot time by appending:

elevator=noop

to the kernel parameters in /etc/grub.conf.

Sure enough, I modified /boot/grub/grub.conf on my Centos 6 boxes and appended elevator=noop to the kernel line, then rebooted. It helped a lot! Performance no longer was pitiful. I’m not nearly as familiar with vmware as I am with Xenserver so this was a good hint.

Analytics, CLI

Fix Splunk lockout after exceeded quota

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Recently I came across a situation with my home install of Splunk (free license) where the 500MB quota was exceeded three days in a row. I hadn’t checked Splunk for a few days so I was completely blindsided by it. The consequence of going over quota three days in a row? Losing the ability to do any searches in Splunk, which is a real downer.

The easiest, although least convenient, way to fix being locked out is to wait it out. If you go 30 days in a row without violating the license, Splunk will unlock itself. Splunk will still receive and index events during that time. The inability to search makes it really difficult to track down what the problem is, though, and I wasn’t happy waiting for 30 days before getting Splunk back.

Poking around on the Splunk forums I discovered that there is a way to get splunk back – perform a fresh install and then migrate your database and settings over to the fresh install. This involves backing up a few things, then copying them over the fresh install’s default folders

  • $SPLUNK_HOME/var/lib/splunk/defaultdb   #Default Splunk index, where all my data is held. If you have other indexes in here you’ll want to copy them too.
  • $SPLUNK_HOME/etc  #all your configuration files

Simply back up the above folders, install Splunk on a new machine, launch Splunk first so it will generate all the default files, then copy the files over to the new instance.

I went a step further and planned for the future. I wrote a quick and dirty script that will do all of this for you,  even on the same machine – no need to copy to another machine.  The script assumes you’re running a redhat derivative and have the correct Splunk install file in a predictable location. Update the locations of splunk directories and install files as needed and run as root.

#!/bin/bash

#Backup important directories
mkdir /opt/splunkbackup/
cp -al /opt/splunk/etc /opt/splunkbackup/
cp -al /opt/splunk/var/lib/splunk/defaultdb /opt/splunkbackup/

#Nuke splunk
/opt/splunk/bin/splunk stop
rm -rf /opt/splunk

#Reload from fresh start
rpm -iv --replacepkgs /home/nicholas/splunk-6.2.2-255606-linux-2.6-x86_64.rpm
/opt/splunk/bin/splunk start --accept-license

#Restore configuration files and indexes
/opt/splunk/bin/splunk stop
rm -rf /opt/splunk/etc
cp -al /opt/splunkbackup/etc /opt/splunk/
rm -rf /opt/splunk/var/lib/splunk/defaultdb
cp -al /opt/splunkbackup/defaultdb /opt/splunk/var/lib/splunk/
chown splunk:splunk -R /opt/splunk/
/opt/splunk/bin/splunk start

#Remove splunk backup
rm -rf /opt/splunkbackup

This will restore your searches, settings, and data. It won’t restore audit and other internal Splunk information, however. This script worked marvelously in getting my Splunk back.

Web

Fix owncloud client sync “not valid JSON!” error

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Recently I migrated my owncloud installation from one webserver to another. I learned that all you have to do is copy the data/ and config/ directories from your owncloud installation to the new machine’s owncloud folder to migrate everything over.

After the migration, I noticed the Windows desktop sync clients stopped working (android worked fine, though.) The main error messasge was not helpful:

Failed to connect to owncloud at https://servername/path/status.php: Unknown error

I found out from here that you can alter the shortcut for the Windows client and append –logwindow to the Target section. Once that was done, I was able to get more information:

03-02 10:01:27:240 0x50f9ec8 networkjobs.cpp:453 status.php from server is not valid JSON!

Manually navigating to status.php in the browser didn’t reveal anything – it appeared to load normally.

After much digging I found a suggestion to check the admin settings within owncloud. This is where I realized I probably didn’t migrate things properly. There was a big warning about invalid .htaccess files. Progress!

The lack of an .htaccess file made me realize that instead of completely moving the entire folder from the old owncloud install to the new, I needed to copy into the existing new owncloud directory. In moving instead of copying I somehow missed a few important files.

I started over, this time copying all files inside data and config into the new owncloud data and config directories. Apparently the Windows sync client requires valid .htaccess configuration before it will work.  Success!