Basic Debian Setup for Squeeze and Wheezy

Recently I've been deploying Debian 6.0 (Squeeze) and 7.0 (Wheezy) servers for some personal projects. These servers are provisioned in different ways:

  • Open Media Vault using a Squeeze pre-seed
  • VPS powered by LXC deployed via debootstrap
  • VPS powered by KVM using the hosting providers Wheezy pre-seed

Consequently the basic install differs on each instance and requires a little bit of post install tweaking to get them all consistent. This blog post is a quick reference for the post install steps I complete on Debian servers.

Timezone & Locale

Select your timezone.

dpkg-reconfigure tzdata

Select your locale(s).

dpkg-reconfigure locales

Make sure the locales are correctly generated. Replace en_GB.UTF-8 with your default locale.

update-locale LANG=en_GB.UTF-8 LANGUAGE=en_GB.UTF-8 LC_ALL=en_GB.UTF-8 LC_TIME=en_GB.UTF-8 LC_CTYPE=en_GB.UTF-8
locale -a
locale-gen

Hostname

echo box.example.org > /etc/hostname
/bin/hostname -F /etc/hostname

Update /etc/hosts accordingly.

Time

Keeping time is essential.

apt-get install ntp ntpdate

Force a clock sync.

service ntp stop
ntpdate -s pool.ntp.org
service ntp start

If your VPS is a Xen DomU then checkout the following.

Essentials

These are the essential tools I require.

apt-get install build-essential curl git htop less \
lsb-release nano rsync screen sudo tree whois

Users

The following will create a user with sudo capabilities.

useradd user_a --create-home --shell /bin/bash --user-group \
--groups adm,dialout,cdrom,plugdev,sudo

This will create a regular user.

useradd user_b --create-home --shell /bin/bash --user-group --groups adm,dialout,cdrom,plugdev

Assign a password.

echo user_a:mypassword | chpasswd

An existing user can be made a sudoer by simply adding them to the sudo group.

adduser user_b sudo

Firewall

I use firewall my VPS server with ufw. This is my initial configuration that allow access via SSH only.

sudo apt-get install ufw

Configuring ufw is simple but make sure you have console access to the host you are configuring just in case you lock yourself out.

NOTE! When enabling ufw the chains are flushed and connections may be dropped. You can add rules to the firewall before enabling it however, so if you are testing ufw on a remote machine it is recommended you perform...

ufw allow ssh/tcp

...before running sudo ufw enable. Once the firewall is enabled, adding and removing rules will not flush the firewall, although modifying an existing rule will.

Set the default behaviour to deny all incoming connections.

sudo ufw default deny

Open up TCP port 22 but with rate limiting enabled which will deny connections from an IP address that has attempted to initiate 6 or more connections in the last 30 seconds. Ideal for protecting sshd but you should conisder other SSH brute force defense techniques as well.

sudo ufw limit ssh

To enable the firewall you also have to do the following.

sudo ufw enable

On low-end servers it might be beneficial to disable logging.

sudo ufw logging off

You can see the status of the firewall using sudo ufw status.

Intrusion prevention

I use either denyhosts

sudo apt-get install denyhosts

Purge entries older than 5 days, denied hosts will only be purged twice and disable email alerts.

sudo sed -i 's/#PURGE_DENY = 5d/PURGE_DENY = 5d/' /etc/denyhosts.conf
sudo sed -i 's/#PURGE_THRESHOLD = 2/PURGE_THRESHOLD = 2/' /etc/denyhosts.conf
sudo sed -i 's/root@localhost//' /etc/denyhosts.conf

Restart denyhosts.

sudo service denyhosts restart

Also see SSH brute force defence.

Boot options

These servers are headless and often remote, therefore I enable fsck auto repair.

Squeeze

sed -i 's/FSCKFIX=no/FSCKFIX=yes/' /etc/default/rcS

Wheezy

sed -i 's/#FSCKFIX=no/FSCKFIX=yes/' /etc/default/rcS

Repositories

lsb-release was installed earlier.

This is what I put in /etc/apt/sources.list.

cat >/etc/apt/sources.list<<EOF
deb http://ftp.uk.debian.org/debian/ $(lsb_release -cs) main contrib non-free
deb-src http://ftp.uk.debian.org/debian/ $(lsb_release -cs) main contrib non-free

deb http://security.debian.org/ $(lsb_release -cs)/updates main contrib non-free
deb-src http://security.debian.org/ $(lsb_release -cs)/updates main contrib non-free

# $(lsb_release -cs)-updates, previously known as 'volatile'
deb http://ftp.uk.debian.org/debian/ $(lsb_release -cs)-updates main contrib non-free
deb-src http://ftp.uk.debian.org/debian/ $(lsb_release -cs)-updates main contrib non-free
EOF

I replace ftp.uk with ftp.us for servers located in the United States.

sed -i 's/ftp\.uk/ftp\.us/g' /etc/apt/sources.list

Backports

I add the Backports repository in order to access some updated packages.

Squeeze

cat >/etc/apt/sources.list.d/backports.list <<EOF
deb http://ftp.uk.debian.org/debian-backports $(lsb_release -cs)-backports main contrib non-free
deb-src http://ftp.uk.debian.org/debian-backports $(lsb_release -cs)-backports main contrib non-free
EOF

Wheezy

cat >/etc/apt/sources.list.d/backports.list <<EOF
deb http://ftp.uk.debian.org/debian $(lsb_release -cs)-backports main contrib non-free
deb-src http://ftp.uk.debian.org/debian $(lsb_release -cs)-backports main contrib non-free
EOF

Update.

sudo apt-get update

All backports are deactivated by default (i.e. the packages are pinned to 100 by using ButAutomaticUpgrades: yes in the Release files. If you want to install something from backports run:

apt-get -t wheezy-backports install "package"

MTA

sSMTP is a simple MTA to deliver mail from a computer to a mail hub. sSMTP is simple and lightweight.

Remove exim4

Some VPS Debian templates from VPS providers have exim4 installed and running by default. Remove it.

sudo service exim4 stop
sudo apt-get purge exim4 exim4-base exim4-config

Install sSMTP

apt-get install ssmtp bsd-mailx

sSMTP Gmail Configuration

I use Gmail as my smart host, here is an example configuration for /etc/ssmtp/ssmtp.conf.

#
# Config file for sSMTP sendmail
#
# The person who gets all mail for userids < 1000
# Make this empty to disable rewriting.
root=root@example.org

# The place where the mail goes. The actual machine name is required no 
# MX records are consulted. Commonly mailhosts are named mail.domain.com
mailhub=smtp.gmail.com:587

# Where will the mail seem to come from?
rewriteDomain=

# The full hostname
hostname=box.example.org

# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address
FromLineOverride=YES

# Gmail requires TLS
UseTLS=YES
UseSTARTTLS=YES

# Username and password for Gmail servers
AuthUser=yourgmailname@gmail.com
AuthPass=youpassword
AuthMethod=LOGIN

Then add each account that you want to be able to send mail from by editing /etc/ssmtp/revaliases:

root:username@gmail.com:smtp.gmail.com:587
user_a:username@gmail.com:smtp.gmail.com:587
user_b:username@gmail.com:smtp.gmail.com:587

Log and package monitoring

My personal VPS server are dotted about the place but I like to keep an eye on them and I find apticron and logwatch are very useful for that.

apticron

apticron is a simple tool to mail about pending package updates.

sudo apt-get install apticron

logwatch

Logwatch is a modular log analyser that runs every night and mails you the results.

sudo apt-get install logwatch

Lighter

Some of my servers have fairly low resources, these are some simple changes that can save a bit of RAM or disk space.

aptitude

I don't use it.

sudo apt-get purge aptitude

D-Bus

D-Bus is a message bus, used for sending messages between applications. Some VPS provider Debian templates have D-Bus and avahi install. I don't require these on Internet facing servers so I remove them. If an application pull in D-Bus as a requirement that is fine, but for this initial server state I remove it.

sudo apt-get purge dbus

at

at provides delayed job execution and batch processing. I don't use it.

sudo service atd stop
sudo apt-get purge at

ngetty

Ngetty is a single-process getty replacement, so instead of running 6 getty processes consuming up to 3MB of RAM each, you can use a single ngetty process using less than 1MB of RAM total.

sudo apt-get install ngetty

Edit /etc/inittab, comment out getty and add ngetty like so.

#1:2345:respawn:/sbin/getty 38400 tty1
#2:23:respawn:/sbin/getty 38400 tty2
#3:23:respawn:/sbin/getty 38400 tty3
#4:23:respawn:/sbin/getty 38400 tty4
#5:23:respawn:/sbin/getty 38400 tty5
#6:23:respawn:/sbin/getty 38400 tty6
ng:2345:respawn:/sbin/ngetty 1 2 3 4 5 6

Restart inittab

telinit q

That about covers the general post installation step I complete on my Debian servers.

Clean up.

Remove any packages that are no longer required and clean up the package cache.

sudo apt-get autoremove
sudo apt-get autoclean
sudo apt-get clean

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