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Posts Tagged → linux

How to build an 8 TB RAID5 encrypted time capsule for 500 Euros

So I wanted to buy a NAS that can act as a time capsule for Apple computers and run a proper Linux at the same time. I also wanted to be able to run the occasional Windows or Linux VM and I wanted to have a lot of storage. As I knew the thing was going to be in our coworking space, it also needed to have disk encryption.

Here’s how I built this for just under €500.00 using standard components and free open source software.

Selecting the hardware components

I found the HP ProLiant MicroServer (see Review and more Picures) to deliver great value for the price. At the time of writing, you can buy it for €209.90 if you’re in Germany like me.

The N36L (which I bought) comes with a single 250GB hard drive which obviously did not meet my “a lot of storage” requirement. So I bought 4 identical Seagate Barracuda Green 2000GB SATA drives which would add another €229.92 to the bill if you bought them today. I am not an expert in hard drives, but the Seagate Barracuda brand was familiar and “Green” sounds good as well.

If you don’t want your new server to host virtual machines at some point, you can probably get out your credit card and check out right now. If you’re like me though, you’d add another 2 bars of 4GB Kingston ValueRAM PC3-10667U CL9 (DDR3-1333) to your cart. The two of them together are just €44.24, so it’s no big deal anyways.

All components together will set you off €484.06. The rest is based on open source software (Debian mostly) which is free as in beer. More about that after the break.

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Are you stuck in Debian/MySQL/Charset/Collation hell?

So while Debian still hasn’t changed the MySQL default caracter set and collation to utf8, we all know that the first thing to do on a vanilla Debian MySQL installation is to add the following utf8.cnf file to /etc/mysql/conf.d/:

[mysqld]
default-character-set=utf8
default-collation=utf8_unicode_ci

However, if for some reason you didn’t do that and have used software which hasn’t been consistently explicit about character sets and collations, you end up with a nice mess of character sets and collations.

There is a great post on serverfault which helps you out. It comes down to one command which will take some time based on the size of your database:

mysql -B -N --user=user --password=secret -e "SELECT DISTINCT \
CONCAT( 'ALTER TABLE \`', TABLE_SCHEMA, '\`.\`', TABLE_NAME, '\` CONVERT \
TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;' ) FROM \
information_schema.COLUMNS WHERE TABLE_SCHEMA != 'information_schema';" \
| mysql --user=user --password=secret

Update:

And of course you need to alter the defaults for existing databases as well:

mysql -B -N --user=user --password=secret -e "SELECT DISTINCT \
CONCAT( 'ALTER SCHEMA \`', SCHEMA_NAME, '\` CHARACTER SET utf8 COLLATE \
utf8_unicode_ci;' ) FROM information_schema.SCHEMATA where SCHEMA_NAME \
!= 'information_schema';" | mysql --user=user --password=secret

First steps with Chef

Today, Jens and I got to play with Chef which supposedly is the hot sh$&!t when it comes to infrastructure automation and such. Installing your own Chef server seems hard at first but will work in the end.

If you’re using Debian, the APT sources will save you some headaches. Just add

deb http://apt.opscode.com/ squeeze main

to your /etc/apt/sources.list and do something like

wget -qO - http://apt.opscode.com/packages@opscode.com.gpg.key | sudo apt-key add -
sudo apt-get update

to be sure to be getting what you asked for. Then, a little sudo apt-get install chef will do the trick to set up a client and sudo apt-get install chef-server will supercharge your node with a fully blown chef server, including but not limited to CouchDB, Solr, RabbitMQ and other fancy stuff. (You’ll want to do this on two different nodes, so use Virtual Box or something.)

After you’ve set up two nodes like that, try following the rest of the instructions in this tutorial and do the first cookbook example, then you’ll have come as far as we have today.

I will update this post as we dig deeper – hopefully later this week.

Bazaar over chrooted sftp

How to set up bzr for chrooted sftp users

How to restrict a user’s access to sftp://.../var/bzr

For the prototyping editor itself and for a lot of our clients’ projects we are heavy Bazaar users at pidoco° to manage our distributed workflow. When we started some years ago we just installed bzr on one of the test servers where all of the developers had ssh access anyway. We put the repositories in /var/bzr and used sftp to checkout/push/pull source changes. This was handy as a sftp server comes with openssh installed.

As the team grew over the years we got to a point where we wanted to give new developers access to the bzr repositories without giving them full ssh access. However we did not want to have to change all the urls for existing repositories. Luckily this can be achieved easily since Debian Lenny.

Per Server Settings

On our scm server we have a user group called bzr that grants read/write access to most of the repositories (except of some personal or release branches) to all users with bzr access. And now we added the group sftponly. All users in this group will be restricted to sftp access only instead of a full shell.

sudo addgroup sftponly
sudo addgroup bzr

You probably have to add ‘/usr/lib/sftp-server’ to /etc/shells to make it a valid shell, eg. like this:

root@host # echo '/usr/lib/sftp-server' >> /etc/shells

The following settings in /etc/ssh/sshd_config force the internal sftp server to be used by openssh and change the root directory for all users in the group sftponly to /var/chroot. Make sure to restart sshd afterwards.

Subsystem sftp internal-sftp
Match Group sftponly
    ChrootDirectory /var/chroot
    AllowTCPForwarding no
    X11Forwarding no
    ForceCommand internal-sftp

Up to now our repositories have been in /var/bzr. These need to be moved to /var/chroot/var/bzr to let the sftponly users access them. /var/chroot needs to have root:root as owner for openssh to work correctly. For the existing ssh users we add a symbolic link to keep the old paths working:

sudo mkdir /var/chroot
sudo chown root:root /var/chroot
sudo mkdir /var/chroot/var
sudo mv /var/bzr /var/chroot/var
sudo ln -s /var/chroot/var/bzr /var/bzr

Per User Settings

giving the user username sftp access, but nor ssh access:

USERNAME=username                                  # give the user a name
sudo adduser ${USERNAME}                           # add user and data to system
sudo usermod -s /usr/lib/sftp-server ${USERNAME}   # disallow ssh/bash, allow ssh/ftp (sftp)
sudo adduser ${USERNAME} bzr                       # allow group access to most bzr folders
sudo adduser ${USERNAME} sftponly                  # disallow access to /, allow access to /var/bzr

This changes user’s shell to sftp-server.

Result

As a result of these settings both normal ssh users as well as restricted users in the sftponly group can use the same url for their shared repositories
bzr checkout sftp://my.domain/var/bzr/my_repository. By using chroot however users in the group sftponly are restricted to using sftp and can only access the folders in the bzr subdirectory.

Sources

In the Debian Administration Weblog you can find information on how to setup an OpenSSH SFTP chroot() with ChrootDirectory and on how to restrict users to SFTP only instead of SSH.

Where am I?

Recently I have been working for several clients where I had to test programs on different servers. The Unix prompt alone doesn’t always tell you which operating system you are logged on and – it gets worse – there seems to be no convention at all on where to store that information. Arun Singh from Novell has written a nice script to determine a Linux distro. However that script does not help you with other Unices and it isn’t installed on any server anyway. So as a note to myself here is a little collection of commands that help to find out the OS your shell is running on. A few further ideas are listed in this German linux forum.

cat /etc/issue*;
cat /etc/*-release;
cat /etc/*version;
lsb-release -a;
cat /proc/version;