Securing an Ubuntu Server

For more current information, see:

Security is relative. Will these steps make your server “secure”? It will be more secure than it was before. And more secure than most servers. Your server will not be “low hanging fruit”. Security is an on-going process. It includes settings, practices and procedures. Make it your business to regularly read about security and to understand the concepts and our system. Paranoia is useful with regard to server security.

I’ve tested what is presented here in Ubuntu Server 10.04 (Lucid) and 10.10 (Maverick). If you want to harden your new Ubuntu server, this is a good start.

Ubuntu server is well designed, regularly updated and relatively secure. The Ubuntu Security Team manifests an onging effort to keep Ubuntu secure. Regular security updates are available and easy to implement.

  • No open ports
  • Role-based administration
  • No X server
  • Security updates
  • Kernel and compiler hardening

In this post, we are going to meet the security challenge in with multi-pronged effort that will include: system analysis, changing settings for additional hardening against attack, installing a firewall maintenance system, scanning for rootkits, and offering a regular maintenance regimen.

  • Change settings for increased security
  • Implement UFW, the uncomplicated firewall
  • Use denyhosts to automatically blacklist attackers
  • Scan the system for vulnerabilities with Tiger
  • Detect attempted intrusions with psad
  • Install nmap and scan the system for open ports
  • Check the system for rootkits with chkrootkit
  • Monitor logs

Change settings for increased security

see also:

Secure shared memory

/dev/shm can be used in an attack against a running service, such as httpd. Modify /etc/fstab to make it more secure.

sudo vi /etc/fstab

Add this line:

tmpfs     /dev/shm     tmpfs     defaults,noexec,nosuid     0     0

Disable root SSH login

The root account is disabled by default in Ubuntu. If you installed Ubuntu on Slicehost or Linode, root is enabled. In any case, it is a good idea to disable root SSH access. Edit /etc/ssh/sshd_config and set PermitRootLogin to no.

sudo vi /etc/ssh/sshd_config

Change PermitRootLogin to no:

PermitRootLogin no

Of course, if you access your server via SSH, you should make sure you have sudo working for your user before disabling SSH root access.

Only allow admin users to use su

This helps prevent privilege escalation.

By default, Ubuntu does not have an admin group. Create an admin group:

sudo groupadd admin

Add yourself to the admin group:

sudo usermod -a -G admin andrew

Restrict access to /bin/su to admin group members:

sudo dpkg-statoverride --update --add root admin 4750 /bin/su

Check permissions for /bin/su with:

ls -lh /bin/su

…and see the following:

-rwsr-x--- 1 root admin 31K 2010-01-26 17:09 /bin/su

Do not permit source routing of incoming packets

see also:

sudo sysctl -w net.ipv4.conf.all.accept_source_route=0
sudo sysctl ­-w net.ipv4.conf.default.accept_source_route=0

Don’t allow system users to access an FTP server

This is only needed is ftpd is installed and running. Only if you’ve installed ftpd. However, it is Ok to do this anyway and it will remove a FAIL from the tiger report.

SFTP is probably better than FTP, if it is usable for your files transfer needs.

see ftpusers manual:

Edit /etc/ftpusers:

sudo vi /etc/ftpusers

Add system users to deny use of ftpd:


UFW: basic firewall

previous post: Ubuntu UFW Uncomplicated Firewall Examples

community documentation:

server guide:

ufw manual:

project wiki:

nice article:

UFW (Uncomplicated Firewall) provides an easy to understand interface to control iptables (iptables conteol Netfilter, which is built into the kernel). Will just a few commands, your server can control access. Checking status is also easy.

UFW (uncomplicated firewall) is a simple interface used to configure iptables.

Install and enable Uncomplicated Firewall:

sudo aptitude install -y ufw
sudo ufw enable

Display available UFW commands:

sudo ufw show

Display UFW configuration:

sudo ufw status

Allow SSH and HTTP access to the Apache server:

sudo ufw allow ssh
sudo ufw allow http

In the above example, ports for OpenSSH and Apache were opened by service name (“ssh” and “http”). You can use a port number instead of the service name (like “80” instead of “http”).

See services running and which names to use:

The practice here is to open only ports that you use – ports that use a service that have a service running. To see a list of services that you have running for which you might want to open ports for:

sudo ufw app list

To see a list of services that UFW uses (like in the “sudo ufw allow ssh” example, above):

less /etc/services

Denyhosts: avoid SSH attacks


Looking at /var/log/auth.log on servers that I manage shows a steady streams of attacks on SSH. I am countering these attacks in a number of ways, starting with denyhosts.

Denyhosts periodically scans /var/log/auth.log for repeated failures to access the system via SSH. It then adds these offenders to /etc/hosts.deny. See the project page for details.

sudo aptitude -y install denyhosts

That does it – the rest is automatic. You can see the IP addresses added to /etc/hosts.deny with:

sudo less /etc/hosts.deny

Tiger: security system scanner


Tiger creates an automated security audit by analyzing files and settings on the system and creating a report listing what has been analyzed and listing warning, alerts and failures.

The tiger command creates a report of potential security problems in /var/log/tiger. The use the tigexp command to look up the resulting codes generated for a detailed explanation and what to do to make the system more secure. The problems tiger considers most serious are marked with FAIL.

It has been a while since Tiger has been updated. It still produces a useful report.

Install tiger:

sudo aptitude -y install tiger

Run tiger to create a report of security issues.

sudo tiger

Use less to view the most recent tiger report:

sudo -i
less /var/log/tiger/`ls -t1 /var/log/tiger | head -1`

Use tigexp to list explanations for FAIL codes:

tigexp dev002f

Google is also helpful, naturally.

Ignore these:

--FAIL-- [dev002f] /dev/fuse has world permissions
--FAIL-- [logf005f] Log file /var/log/btmp permission should be 660

Changing permissions for these could cause problems.

Detect attempted intrusions with psad


Psad is a collection of lightweight daemons that log attempted intrusions, in particular monitoring iptables.


sudo aptitude -y install psad

The daemons will run automatically.

To check current status:

sudo psad -S

You can modify psad settings to e-mail the admin in the event of intrusion detection.

Nmap: port scanning


This allows you to see which ports are open, verifying that UFW/iptables is working correctly.

Installing nmap:

sudo aptitude install -y nmap

Port scanning:

nmap -v -sT localhost

SYN Scanning:

sudo nmap -v -sS localhost

scan type explanations:

Chkrootkit: check for rootkit presence


Chkrootkit scans the system for evidence that a rootkit has been installed.

This is a confidence test to be used to test whether your system has been compromised. In a perfect world you would not need this…but in this world, it is good to run periodically.

Installing chkrootkit:

sudo aptitude install -y chkrootkit

Running chkrootkit:

sudo chkrootkit


Ubuntu community documentation:

The most detailed and informative logs in the world are useless if no one looks at them. Logwatch winnows the deluge to a succinct report…which you will look at. Even so, familiarize yourself with your system’s logs and review them on a regular basis. A daily logwatch habit would be a good start.


sudo aptitude -y install logwatch


sudo logwatch | less

Ongoing maintenance

Your server is now more secure. Once a week, perform on-going maintenance.

Updating software:

sudo aptitude update
sudo aptitude safe-upgrade

The safe-upgrade action is preferred by me because it does not upgrade packages that rely on dependencies that have not been upgraded to required levels.


Or, you could set-up automatic security updates, if you cannot do the weekly maintenance. This is not a perfect solution because an administrator is not monitoring what is being updated and testing after updates. see:

Check for attempted instrusions:

sudo psad -S

UPDATED: Analyze system with tiger. Because the tiger reports in /var/log/tiger/are owned by root, run these commands one at a time. (This solves a problem some people were having with permissions.)

sudo -i
grep FAIL /var/log/tiger/`ls -t1 /var/log/tiger | head -1`

In the above, FAILs are pulled from the newest report file with grep. The ls clause in backticks gives grep the newest file in the directory. The sudo -i command allows you to run multiple commands as root, ending with exit.

Use tigexp to list explanations for FAIL codes:

tigexp dev002f

Scan ports with nmap:

sudo nmap -v -sS localhost

Check for rootkits

sudo chkrootkit

Look at logs:

sudo logwatch | less

Keep up with trends



Ubuntu command line: see PDF of a man page

So, you use the command line. And, you’d like to look at a command’s manual page.

Wouldn’t it be handy to open the page into another window, nicely formatted, all typeset and neat? That is exactly what this little script will do.

I keep my personal scripts and executables in ~/bin (the bin directory inside my home directory). My ~.profile file in Ubuntu already had that in the path, if ~/bin exists.

If needed, create ~/bin:

mkdir ~/bin

Create a shell script called ~/bin/gman with these lines:

#!/bin/sh -e
man -t $1 | ps2pdf - > "/tmp/$"
gnome-open "/tmp/$"

Make the shell script executable with:

chmod +x ~/bin/gman

If needed, exit your shell and open it back up again. This would be to ensure that ~/bin is detected and added to your PATH.

Then, to use it, just type gman and the command you are interested in, ie. grep.

gman grep

This will show you a beautiful, formatted document:

List of installed packages on Ubuntu

This lists packages added after Ubuntu was installed.

When I upgrade from one version of Ubuntu to another, I do a fresh install. I have a procedure on my personal wiki with all of the steps to move in. Part of that is restoring data from backup, Part is restoring or recreating configuration files.

But what about software packages? There is a baseline of packages that I use all the time, but I also add packages ad hoc as required. It is convenient to get a list of what is installed.

Here’s a one-liner to list installed packages on Ubuntu:

cat /var/log/installer/initial-status.gz | gzip -d | grep '^Package:' | awk '{ print $2}' > tmp.txt && aptitude search -F %p '~i!~M' | awk '{ print $1}' | grep -v -F -f tmp.txt && rm tmp.txt

The list that is returned is pretty good. You can save the output to a text file and edit that file to get the list of packages you want to install on the new system.

Here’s how to output to packages.txt:

cat /var/log/installer/initial-status.gz | gzip -d | grep '^Package:' | awk '{ print $2}' > tmp.txt && aptitude search -F %p '~i!~M' | awk '{ print $1}' | grep -v -F -f tmp.txt > packages.txt && rm tmp.txt

As you can see, it greps out a list of packages included in the original install, grabs the second field with awk and stuffs the result in a temporary file. Then a list of installed packages is generated, again using awk to parse out the package name field. Then grep is used to compare thee two lists and output just the packages installed after initial installation.

Here is what I have installed:


So, this is a list of 40 packages installed on my machine, out of a total of 1560 packages returned by “dpkg –list” (thanks, Mark!). Just those I installed, not everything including all of baseline Ubuntu.

Interactive, Full Screen Aptitude

Debian’s aptitude command is, according to their documentation, the preferred program for package management. I use Ubuntu for my work machine and servers and have found aptitude to be easy to understand and use, as well as reliable.

see also: Aptitude vs Apt-get Comparison

Unlike apt-get, aptitude offers a full-screen (or full-window more likely) mode that can be used to interactively manage packages on a Debian or Ubuntu system. As is often the case, a combination of command line operation and an interactive utility prove to be very attractive and useful.

You might use command line mode most often, to install, remove and upgrade packages, and sometimes use the interactive mode to check the status of your system and mark packages to manage how particular packages are dealt with.

To start in interactive mode, simply enter aptitide, with no subcommands:


note: You do not need to sudo aptitude because, in interactive mode, it will prompt you and run sudo itself, if needed. Oh, the convenience!

Right away, you will see the interactive mode user interface:

Drop-down menus

The interactive interface includes drop-down menus at the top of the display. These are accessed with control-r or F10. Many of the of the commands available have a shortcut command key available, listed on the right side of the menu choice.

A full list of menu commands can be found here:

Package categories

Packages are shown in groups, organized by the following categories:

category explanation
New packages Packages that have been added since the list of new packages has been cleared (with the f command).
Installed packages Packages that are installed on the computer.
Not installed packages Packages that are not installed on the computer.
Obsolete and locally created packages Packages that are installed on the computer, but not available from an apt source.
Virtual packages Pseudonymous for other packages for compatibility or convenience.
Tasks Groups of packages that offer an easy means to install groups of packages for some purpose.

While the user interface is pretty well designed, it can be tricky to use because a variety of single letter codes are displayed and commands are entered via arcane single letter commands.

Navigation command keys

key action
F10 or control-t Show the drop-down menu
? Show help
Arrow keys Navigation
Enter key Select
+/- keys Mark a package to be installed, updated or removed
g key* Go forward: preview/confirm actions
q key* Go back: quit

* The q command quits the current operation and goes back to the previous mode. When at the top level, the q command quits the program. In general, the g goes forward and the q goes back.

Example workflow

  • press u to update local list of available packages
  • press U to mark upgradable packages
  • press g to review pending actions (modify if desired*)
  • press g (again) to start the process

Press g twice? Yes, the first time results in a list of packages that will be processed and the second time completes the action. This gives you a chance to review the changes before proceeding.

If you’ve erred, you can select ‘Cancel pending actions’ in the ‘Actions’ menu.

*When reviewing pending actions:

  • a explicitly accepts an action (press it again to un-accept).
  • r rejects a pending action.
  • g again goes ahead with pending actions.

Common actions

Use control-t for the drop-down menu to see all available actions. All of these commands are found in the Actions drop-down menu.

shortcut key item in Action menu action
g Install/remove packages Show preview, or if preview visiable, perform actions
u Update package list Update local package list from Internet sources
U Mark Upgradable Flag upgradable packages
f Forget new packages Clear “new” packages list
Q Quit Quit aptitude

Common package commands

These commands are found in the Package drop-down menu.

shortcut key item in Action menu action
+ Install Marks package for installation
- Remove Marks package for removal
i Cycle Package Information Changes information displayed for selected package

Current state flags

These flags appear in the first column of a table of packages when you’ve drilled down in one of the categories.

flag meaning
i Package is installed and all its dependencies are satisfied.
c Package was removed, but its configuration files are still present.
p Package and all its configuration files were removed, or the package was never installed.
v Package is virtual.
B Package has broken dependencies.
u Package has been unpacked but not configured.
C Half-configured: the package’s configuration was interrupted.
H Half-installed: the package’s installation was interrupted.

Position of the Current State and Action flags in the Package lists:

Action flags

These flags appear right after the current state flag in column one of displayed packages when you’ve given a command to make an alteration. One or more action flags will appear.

flag meaning
i Package will be installed.
u Package will be upgraded.
d Package will be deleted: it will be removed, but its configuration files will remain on the system.
p Package will be purged: it and its configuration files will be removed.
h Package will be held back: it will be kept at its current version, even if a newer version becomes available, until the hold is cancelled.
F An upgrade of the package has been forbidden.
r Package will be reinstalled.
B Package is broken: some of its dependencies will not be satisfied. aptitude will not allow you to install, remove, or upgrade anything while you have broken packages.


Aptitude vs Apt-get Comparison

see also: Interactive, Full Screen Aptitude

One of the many attractive features of Ubuntu and Debian Linux is the package management system. Coming from other operating systems and other distributions makes the discovery of the Advanced Packaging Tool, APT, a source of pleasure and delight. Here is a system that solves dependency hell, makes keeping soft up to date easy and facilitates simple installation and removal of software packages.

The mainstay of this system has been apt-get, an extremely useful and versatile program that has been the heart of the Debian APT system. A great and useful program, but not perfect, the newer program aptitude is the result of an effort to improve on apt-get. In addition to a cleaner command line interface, aptitude offers a fullscreen character-based UI and more complete tracking of what has been installed and interdependencies.

aptitude is a newer and improved replacement for apt-get

These two programs provides higher level capabilities compared to dpkg, the Debian low-level package management utility. They offer an interface to package repositories and provide relief from dependency hell.

feature apt-get command aptitude command
fullscreen interface N/A aptitude
install package apt-get install ‘pkgname’ aptitude install ‘pkgname’
remove package apt-get remove ‘pkgname’ aptitude remove ‘pkgname’
purge package (removes package
and installation files)
apt-get –purge remove ‘pkgname’ aptitude purge ‘pkgname’
upgrade installed packages apt-get upgrade aptitude upgrade
upgrade installed packages
even if other packages
must be removed
apt-get dist-upgrade aptitude dist-upgrade
show package details (apt-cache show ‘pkgname’) aptitude show ‘pkgname’
search for packages (apt-file ‘searchpattern’) aptitude search ‘searchpattern’
delete installation files apt-get clean aptitude clean
delete obsolete installation files apt-get autoclean aptitude autoclean
update local cache of
available packages
apt-get update aptitude update
Show package details apt-get show ‘pkgname’ aptitude show ‘pkgname’
Retain the current version
of a package going forward
N/A aptitude hold pkgname
Clear the hold on a
package from
‘aptitude hold pkgname’ command
N/A aptitude unhold pkgname
List reverse dependencies apt-cache rdepends packagename aptitude -D packagename
super cow powers apt-get moo aptitude -v[v[v[v[v]]]] moo

As you can see, in addition to a more complete dependency tracking solution, aptitude also provides a (well designed) full-screen interface and cleaned-up command line syntax. Also, contrary to reports elsewhere, aptitude offers the ever important super cow functionality, with sarcasm added (Easter egg).

When installing a package, aptitude will show which other packages, though not required, are recommended or suggested, so you can decide whether or not to also install those.

Because aptitude more completely track dependencies, if you use it exclusively your will not need to use deborphan or debfoster.

Apt-get does not remove packages it installed as dependencies when the package you specified to be installed is removed. Aptitude does remove unneeded dependencies. This basic difference can cause problems when switching from apt-get to aptitude.

Don’t use both apt-get and aptitude interchangeably

Use one or the other. I’ve switched completely from using apt-get to using aptitude. If you do use apt-get, afterward run aptitude and fix any problems detected by first pressing g, which will show broken dependencies and packages that aptitude would remove. If you want to retain the packages that would be removed, arrow down to the header of that category and press the + key. Pressing g again will update your system with your indicated changes.

There is a difference in how aptitude keeps track of installed packages and their dependencies compared to apt-get. Aptitude is more precise is tracking these dependencies. Consequently, when you switch from using apt-get to aptitude, the first time you use aptitude you can run into problems because it can remove needed packages because it does not know that they are needed. This can be resolved through aptitudes’s full-screen interface or by entering the following command:

sudo aptitude keep-all

This will cause aptitude to retain all current packages going forward.

Aptitude’s full-screen interface

As displayed in the comparison table, aptitude offers a character-based full-screen interactive user interface if aptitude is entered as a command with no options.

The interface is very well designed and implemented, logical and easy to use after a few minutes of examination and trial. It has a drop-down menu system, which I found to work well using a mouse. The help system can be access via the drop-down menu or by pressing the ‘?’ key. A plethora of options are presented, most of which will make sense from what you’ve seen in the command line operation of the program. Pressing ‘q’ exits help…indeed pressing ‘q’ is the way to exit other modes in the program and exiting the program itself.

Other thoughts

I’ve found aptitude to be so well done, that I use it for all my package management needs. I use Synaptic to help search for software sometimes, whether for my local machine or a server. Then, I install it with aptitude…in any case Synaptic would be pretty useless over SSH to a server.

Some pages I found helpful: and

Mix in some CLI fun on your server

This post is directed at Ubuntu and Debian server admins. As all work and no play makes Jack a dull boy, it is imperative that you immediately make your server more fun. If you do not get a little smile when you log into your server via SSH, then something is terribly wrong! Avoid dullness by all means.

Here I will show how to add and use figlet, fortune, cowsay and xmlstarlet to have big banners, random quotes’n’quips, talking cows and word of the day appear when using SSH to access your server.

FIGlet is a program for making large letters out of ordinary text.

FIGlet project:

Fortune is a simple program that displays a random message from a database of quotations.

Cowsay is a filter that takes text and displays a cow saying it.

Cowsay project page:

Cowsay article:

XMLStarlet is a set of command line utilities (tools) which can be used to transform, query, validate, and edit XML documents and files using simple set of shell commands in similar way it is done for plain text files using UNIX grep, sed, awk, diff, patch, join, etc commands.

XMLSartlet project page:

Adding Universe and Multiverse Repository in Ubuntu

These packages are in the Universe and Multiverse repositories. If you need to add these repositories, just un-remark the pertinent lines in /etc/apt/sources.list and run aptitude update:

First, make a backup of the original /etc/apt/sources.list file.

sudo cp /etc/apt/sources.list /etc/apt/sources.list.original

Edit /etc/apt/sources.list:

sudo vi /etc/apt/sources.list

Un-remark the universe and multiverse lines (remove the leading # character) so the lines look something like this:

deb lucid universe
deb-src lucid universe
deb lucid-updates universe
deb-src lucid-updates universe
deb lucid multiverse
deb-src lucid multiverse
deb lucid-updates multiverse
deb-src lucid-updates multiverse

Finish by retrieving the updated package lists to your system with:

sudo aptitude update

By the way, to search for packages in the Ubuntu packages repositories, visit:


Figlet creates character graphic block letter banners. Thus:



                       ___      ___ 
   ____ ___  ___  ____/ (_)___ |__ \
  / __ `__ \/ _ \/ __  / / __ `/_/ /
 / / / / / /  __/ /_/ / / /_/ / __/ 
/_/ /_/ /_/\___/\__,_/_/\__,_/____/ 

Install Figlet

On an Unbuntu/Debian system, install figlet like this:

sudo aptitude install figlet

The following will create the media2 banner, as above:

figlet -f slant media2

Modifying Message of the Day

Once you are satisfied with the output of figlet, you can have your character graphics banner appear whenever a user uses SSH to access the server, just modify the /etc/motd.tail file with:

sudo figlet -f slant media2 >>/etc/motd.tail

Bingo, whenever a user logs into the media2 server then will see your nifty banner! A little dullness have been bannished.

Installing xmlstarlet, cowsay and fortune

These are the commands we’ll be using to offer some fresh content on every login.

sudo aptitude install xmlstarlet cowsay fortune

Putting it all together

Modify the /etc/bash.bashrc file. This affects all users that use bash as their default shell.

fortune -a | cowsay -f $(ls /usr/share/cowsay/cows/ | shuf | head -n1)

echo -n "word of the day: "
/usr/bin/xmlstarlet sel --net -t -m "/rss/channel/item/description" -v "." ""

The fortune command pops out a random quip, piped into cowsay, which is configured here with -f to use a random character graphic image. Then, word of the day is sourced from an RSS feed with xmlstarlet.

With everything, here is an example of what will appear when your SSH into your server:

Linux ijuki 2.6.32-x86_64-somewhere #1 SMP Sat Dec 5 16:55:26 UTC 2009 x86_64

                       ___      ___ 
   ____ ___  ___  ____/ (_)___ |__ \
  / __ `__ \/ _ \/ __  / / __ `/_/ /
 / / / / / /  __/ /_/ / / /_/ / __/ 
/_/ /_/ /_/\___/\__,_/_/\__,_/____/ 

Last login: Sun May  2 18:39:14 2010 from
/ Everything that you know is wrong, but \
\ you can be straightened out.           /
       \    ____
        \  /    \
          | ^__^ |
          | (oo) |______
          | (__) |      )\/\
           \____/|----w |
                ||     ||

word of the day: sesquipedalianism: given to using long words.

Ubuntu UFW Uncomplicated Firewall Examples

See also: Securing an Ubuntu Server

UFW community documentation:

UFW server documentation:

UFW page:

Implementing a basic firewall on your Ubuntu server is simple.

UFW (Uncomplicated Firewall) is a simple configurator for Netfilter, the packet filtering system that is built into the Linux kernel. This will then filter IP packets that arrive at the server by port number. Port numbers are nothing magical, just an integer in the packet header that gets mapped to a service, like your web server. All the packets arriving with a certain port number are mapped to a service.

By default, when you turn on UFW, everything is filtered. Then, with very simple commands, you set rules to allow just the services you are providing. If you are just providing a web server, you would allow only the port needed for that.

Turning UFW on

By default, UFW is turned off. To turn it on:

sudo ufw enable

That is all there is to it. UFW is now running. When your system reboots, UFW will be started automatically.

Allowing SSH

By default, SSH uses port 22. Of course, you can configure OpenSSH to use a different port number…then open that port instead of 22.

sudo ufw allow 22

…or you can use the service name instead of the port number:

sudo ufw allow ssh

…or you can use the service application name instead of the port number:

sudo ufw allow OpenSSH

To get a list of service applications:

sudo ufw app list

The concept to retain is that rules can be set with a port number (22) or service name (ssh) or application name (OpenSSH).

Allowing Apache

By default, HTTP severs use port 80.

sudo ufw allow 80

…or you can use the service name instead of the port number:

sudo ufw allow http

…or you can use the service application name instead of the port number:

sudo ufw allow Apache

View status

To see the current status of UFW on your server:

sudo ufw status verbose

Example output:

Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing)
New profiles: skip

To                         Action      From
--                         ------      ----
22                         ALLOW IN    Anywhere
80/tcp                     ALLOW IN    Anywhere

A little more

The /etc/services (text) file is used to map service names to port numbers. This can be used to find out which ports are mapped to which services. The vast majority of the designations in this file are not implemented on a given system. This file’s main purpose is to allow service applications (programs) to get the port number to use for a service being provided.

Rules can be set with any of the following:

  • port number
  • service name
  • application name

List names service names

cat /etc/services

List available application names

sudo ufw app list

List implemented services and assigned ports

sudo lsof -i -nP

List active network connections

sudo netstat -p

UFW Help


sudo ufw help

Help output:

Usage: ufw COMMAND

 enable                          enables the firewall
 disable                         disables the firewall
 default ARG                     set default policy
 logging LEVEL                   set logging to LEVEL
 allow ARGS                      add allow rule
 deny ARGS                       add deny rule
 reject ARGS                     add reject rule
 limit ARGS                      add limit rule
 delete RULE|NUM                 delete RULE
 insert NUM RULE                 insert RULE at NUM
 reset                           reset firewall
 status                          show firewall status
 status numbered                 show firewall status as numbered list of RULES
 status verbose                  show verbose firewall status
 show ARG                        show firewall report
 version                         display version information

Application profile commands:
 app list                        list application profiles
 app info PROFILE                show information on PROFILE
 app update PROFILE              update PROFILE
 app default ARG                 set default application policy

XAMPP on Mac OSX with Virtual Hosts

XAMPP is an all-in-one LAMP development solution for multiple platforms. I use Linux on my main computer and OSX for my laptop.

I’ve selected XAMPP to provide the LAMP environment on my Mac. It is free, in on-going development and works well.

Because I have several projects in development at once, I need to be able to quickly update my Mac with the current state of a project and then develop and test. Subversion is part of that equation and Komodo IDE is too. Setting up LAMP on Linux is a snap, but installing everything on the Mac, even with MacPorts would be tedious. There are a few pre-packaged solutions, including XAMPP, MAMP and Zend Server. I chose XAMPP after a little research and it has worked well for me.

The Apache virtual server does not come enabled by default, so a little setup is needed.

Folder for virtual websites

Create the folder “www” in your home directory, this example is in Terminal:

cd ~
mkdir www

This is the folder where you will place each of the virtual site directories. You could just as well put this somewhere else, but a “www” directory here makes sense to me.


Add the following to /Applications/XAMPP/etc/httpd.conf

	Options Indexes FollowSymLinks ExecCGI Includes
	AllowOverride All
	Order allow,deny
	Allow from all

In the above you will need to substitute your username for “yourusername”. This simply sets some Apache settings for the folder where your virtual sites will be.

In this same file find:

# Virtual hosts
#Include /Applications/XAMPP/etc/extra/httpd-vhosts.conf

…and un-rem out the Include line. This enables virtual hosting. Yay!


For each website, add a code block to /Applications/XAMPP/etc/extra/http-vhosts.conf

    DocumentRoot "/Users/yourusername/www/"
    ErrorLog "/Users/yourusername/www/"
    CustomLog "/Users/yourusername/www/" common

In the above, just follow the same pattern I’ve shown for this example site. Don’t vary from this unless you want to do some research and testing. You can see I place a “public” folder insite the top directory for a particular virtual site – put your web documents to serve here.

hosts file

Edit your /etc/hosts file to add “” (your version of this) to a line starting with “” like this:

Restart Apache

Using the XAMPP control stop and re-start Apache.


SSH trick: temporarily return to your local shell

If you are using SSH to access a command shell on a remote system and you would like to temporarily return to a shell on your local system, there is an easy way to do so.

Simply type a tilda (“~”) and control-z.

This will place your SSH session into the background. You will be in a shell on your local system.

You can get the job number of the SSH session with:


Then, to return to the remote session (assuming that the job number you saw when you entered the above command was “1”), enter:

fg 1

Note that the remote shell will not print the prompt, press enter once to see the remote session prompt again.