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Items by Tincho

Debian Package of the Day

ferm: a straightforward firewall configuration tool

Posted: December 14th, 2008, 7:00am CST by Tincho
Article submitted by David A. Thompson. We’re running out of articles! If you like Debian Package of the Day please submit good articles about software you like!

Grumble… a postgresql server on an old Sun workstation isn’t visible to another old Sun workstation which (in theory…) is storing data on the postgresql server. The culprit was a misconfigured firewall. Rather than wading through a bunch of iptables commands, it seemed time to revisit the world of iptables front-ends on the off-chance there was an undiscovered treasure I’d missed on earlier visits. It turns out that there was one: ferm.

A revisit to firestarter, a straightforward GUI interface, ended when firestarter segfaulted and then, when started again, automatically started its firewall. Fortunately, I had altered the firestarter rule set and opened port 22 before firestarter segfaulted. Otherwise I would have been hundreds of miles away from an inaccessible server. After firestarter crashed again with a memory error, I decided to move on…

Like several other firewall front-ends, ferm is aware of the issues associated with working on servers hundreds of miles away from one’s physical location. Ferm starts with a default configuration which leaves the default SSH port open. Even better, ferm has a ‘try-before-you-buy’ feature (shared with a few other packages such as firehol): ferm --interactive activates a specific ruleset and, if a user response isn’t given within 30 sec, the system reverts to the previous ruleset.

Rather than using a GUI interface (e.g., firestarter, gnome lokkit, guarddog, kmyfirewall, knetfilter, …), ferm is configured via a text configuration file and can be controlled in a straightforward manner from the console. This may be a desirable feature for running on a box with limited disk space as GUI interfaces generally require the presence of X windows-related packages, often along with several KDE- or Gnome-related packages.

My main concern wasn’t with whether the application had a GUI or console interface but was with whether the application facilitated straightforward configuration of an iptables ruleset (translation: it shouldn’t take 20 min of reading documentation to get a simple firewall up). Other front-ends (e.g., shorewall and firewall builder) appear to be designed for complex rule-sets and require a substantial investment of effort to learn the syntax of configuration files or a ‘rule-making language’.

Along with ferm, another front-end, firehol seemed to also hit the mark with respect to having a straightforward syntax. Unfortunately, I found that firehol ended up being a time-consumer. In my experience, preparing a firehol configuration file which didn’t trigger multiple errors from firehol/iptables did not prove to be straightforward. In contrast, ferm gave me no such problems. A few tweaks of the default system configuration file —primarily opening a few ports—:
```
  proto tcp dport ssh ACCEPT;
  proto tcp dport http ACCEPT;
  proto tcp dport https ACCEPT;
  proto tcp dport postgres ACCEPT;
```
A simple /etc/init.d/ferm restart and things were running smoothly. Minimal effort, satisfying results…

The bottom line is that, for simple rulesets, using ferm is definitely easier than preparing iptables rules by hand. However, ferm can also be used to put together more complex firewall rulesets. It uses a reasonably powerful configuration language (including support for variables, function definitions, and arrays) which facilitates addressing more complex situations than the one I faced. To top it off, ferm seems to be under active development with bugs being squashed and features being added relatively regularly.

ferm has been available in Debian since Etch and in Ubuntu since Dapper.

Update, editor’s note: I’d like to add to this article my personal experience with ferm. Being a SysAdmin, I’ve been using netfilter/iptables for many years, after migrating away from ipchains; and the day I’ve found ferm my work changed completely. To me, being able to write your rules in clean structures, with blocks, variables and ‘functions’ is, by far, the most important feature of ferm. Thanks to this, I was able to write very complicated rule-sets, which were still readable to the point that the more junior SysAdmins, with little exprience on netfilter, have no difficult modifying it to open up ports or creating a new NAT rule.

Having said that, a warning to the newcomers to netfilter: there’s no tool that will magically allow you to write non-trivial rule-sets if you don’t understand the underlying stuff. You will be able to manage your home server, but if you want to do more serious work, you’ll need to really understand how TCP/IP works, and after that, read a lot about the details of routing and packet filtering in Linux. Having seen many people get frustrated by this, is better for you to know that this beast is quite tricky.
Apt-P2P: peer-to-peer downloading of Debian packages

Posted: November 8th, 2008, 11:00pm CST by Tincho
Article submitted by Cameron Dale. Guess what? We still need you to submit good articles about software you like!

Do you want to help out the Debian (or Ubuntu) project with some mirror bandwidth but don’t know how? Do you want to contribute somehow to Debian’s infrastructure, but you’re not a coder? Tired of getting slow download speeds when the mirrors are overloaded after a new release? Then Apt-P2P is for you.

After installing the apt-p2p package and making some minor changes to apt’s sources, all the files you download with apt (or aptitude, synaptic, gnome-apt, etc…) will be shared with other users, and any files you download will use other users (peers) to download from. However, if no other users have the file you want there’s no need to worry, Apt-P2P will happily fall back to downloading directly from the mirror so your download will not fail.
How it works
Apt-P2P is a daemon that runs in the background, responding to any requests from apt for files to download, and sharing any downloaded files with other users. The sharing is all done using HTTP, so it operates as both a server for the requests from apt and other peers, and as a client to download from other peers and mirrors. Also, if you go to [localhost:9977] in your browser on the machine Apt-P2P is running on, you will get a nice statistical display of what it is doing.

The main operation of Apt-P2P is the maintenance of a Distributed Hash Table (DHT) used to find and store peers to download from for each file. Whenever you download a file, apt-2p will first lookup the SHA1 hash of the file in the DHT. If it is found and has peers listed, then the downloading will occur from the peers (if there are only 1 or 2 peers, the mirror is used as well to speed up the download). If it is not found then the file is requested directly from the mirror. Once the download is complete, a new value is added to the DHT using the SHA1 hash of the file as the key, and including your contact info, so that other peers can then find you to download the file from.

That’s just a brief overview, but there are many hidden details that make things go smoother. For example, for larger files the SHA1 hashes of pieces of the file are stored in the DHT as well, which allows downloaders to break up large files among several peers to get better download speeds (similar to BitTorrent). For more information, you can go to the Apt-P2P home page: [www.camrdale.org].
Comparison with other P2P programs
Other than DebTorrent, there aren’t any other peer-to-peer downloaders available for apt. There was apt-torrent, but it was never packaged in Debian, and now seems to be dead (no updates in 18 months). Comparing Apt-P2P with DebTorrent, Apt-P2P:
- Is faster at downloading from mirrors.
- Uses much less memory and a little less CPU.
- Can download almost all files (source files, Packages.bz2, etc…) from peers, not just .deb packages.
- Works with only the information apt has, no need for other files.
- Doesn’t require a new apt transport for communicating with apt.
- Is more modular and easier to understand as it is based on existing technologies (e.g. twisted).
Setup
Apt-P2P is available in testing (lenny) and unstable (sid), and will be available in Intrepid for Ubuntu. It can be installed by aptitude install apt-p2p.

First, it is VERY important to set up port forwarding if your machine is behind a firewall or router/NAT. The default port you need to forward is 9977, both UDP and TCP. More information on how to determine if you are reachable can be found here.

Setting up apt to use Apt-P2P as a proxy is easy, especially if you have used other proxy software (e.g. apt-proxy, apt-cacher, approx) in the past. The configuration change is the same, simply adding a localhost:9977/ to the front of the entries in your /etc/apt/sources.list file. For example, if you previously had this:
```
# Official
deb http://ftp.us.debian.org/debian etch main contrib non-free
deb-src http://ftp.us.debian.org/debian etch main contrib non-free

# Security Updates
deb http://security.debian.org/ etch/updates main contrib non-free
deb-src http://security.debian.org/ etch/updates main contrib non-free

# Unofficial
deb http://ftp.debian-unofficial.org/debian etch main contrib non-free restricted
deb-src http://ftp.debian-unofficial.org/debian etch main contrib non-free restricted

# Backports
deb http://www.backports.org/debian etch-backports main contrib non-free
deb-src http://www.backports.org/debian etch-backports main contrib non-free
```
Then, if you only want to share the official and backported packages, you would change it to this:
```
# Official
deb http://localhost:9977/ftp.us.debian.org/debian etch main contrib non-free
deb-src http://localhost:9977/ftp.us.debian.org/debian etch main contrib non-free

# Security Updates
deb http://security.debian.org/ etch/updates main contrib non-free
deb-src http://security.debian.org/ etch/updates main contrib non-free

# Unofficial
deb http://ftp.debian-unofficial.org/debian etch main contrib non-free restricted
deb-src http://ftp.debian-unofficial.org/debian etch main contrib non-free restricted

# Backports
deb http://localhost:9977/www.backports.org/debian etch-backports main contrib non-free
deb-src http://localhost:9977/www.backports.org/debian etch-backports main contrib non-free
```
Then, run an apt-get update and start installing packages.

The apt-p2p package is fairly new, so it’s available only in the testing and unstable distributions of Debian, and in the just released Intrepid Ibex, from Ubuntu.
Synfig: the free software alternative for 2D animation

Posted: November 2nd, 2008, 12:00am CDT by Tincho

Article submitted by Carlos López González. Guess what? We still need you to submit good articles about software you like!

For a long time 2D animation software has been dominated by proprietary software. Other common multimedia tasks such as video playing, editing, raster and vector 2D graphics and 3D graphics or animation are currently being covered properly by free software / open source (FOSS) but there wasn’t enough FOSS alternatives for computer aided 2D animation.

Synfig increases the 2D animation software available with a brilliant and professional piece of software.

Synfig was primary developed by Voria, an animation company founded by Robert Quattlebaum who was also the lead software engineer of the software. In 2004 Voria shut down and was discontinued. Fortunately Robert decided to license Synfig under the GNU GPL and turned it over the free software community to develop and use.

Synfig has no comparable alternative software in the FOSS world. Unlike other FOSS that can be used to produce 2D animation (ktoon, pencil) in the “traditional” frame to frame animation, the Synfig workflow is based on vector primitives and their interpolation in time. This drastically reduces the amount of work to produce professional animations because the manual tweening from pose to pose is eliminated, without the need to draw each frame individually.

But this is not the only feature of Synfig…

In Synfig, every primitive or transformation is parametrically generated, which gives extreme flexibility during animation and doesn’t restrict artistic expression. Also, those parameters are calculated on a float point basis obtaining smooth results at any size and any frame rate. Additionally it is possible to link any compatible parameter between any two or more different layers, even placed in different canvases or even convert most of the parameters into a mathematically calculated formula, this allows Synfig to produce particle effects, path based brushes, vectors dynamically linked to any place of a curve and other interesting stuff.

In Synfig there are an extensive set of primitives and transformation layers: Blurs (3), Distortions (6), Colour Filters (5), Fractals (2), Geometry Primitives (8), Gradients (6), Transform (3), Stylize (2) Text, Plant, Duplicate, etc. which provide a complete set of tools in the artist’s hand.

Finally in Synfig is easy to reuse libraries, group scattered layers to manage them like a single one, there are 22 different blend methods… If you want to dig synfig visit its web page. You can find there more info about the usage, the features and its development. Behind it, there is a small but friendly community.

All those features make Synfig a great application but it has also some weak points: there are some missing features not completely developed like the support of sound or saving and loading colour palettes.

On the other hand although the interface of Synfig-Studio can be strange for the first contact (most of the actions are found in the right click context menu), once you understand how it works it is very efficient. I’ve been working with it during last year and I’m completely in love with it. I only miss a quick render engine for editing animation because the current one is quite slow for a normal workflow.

Although it is relatively young it has definitely turned into a program that any 2D artist must have on their GNU/Linux box. It’s been available in Debian since Lenny and in Ubuntu since Feisty.
smartmontools: control the health of your hard disk

Posted: October 12th, 2008, 12:00am CDT by Tincho
Article submitted by Noel David Torres Taño. Guess what? We still need you to submit good articles about software you like!

One of the packages I manually install in every new installation is smartmontools. I’ve some expertise in managing computers and networks, and it is a fact that pirate hackers and software bugs are not the main cause of problems in small and medium installations. Hardware is.

Thus, you have hardware that can fail, and Murphy says that if it can fail, it will. The point is not to avoid hardware failures, which would be impossible, but to detect them early or even prevent them.

Particularly for hard disks, the tool in charge is smartctl from the package smartmontools. IDE disks (if they’re not of the age of dinosaurs) have an integrated self-testing tool called SMART which means “Self-Monitoring, Analysis and Reporting Technology”. Modern SCSI disks have it too if they’re SCSI 3 or newer. It happens that inside the disk chipset there are routines to check parameters of disk health: spin-up time, number of read failures, temperature, life elapsed… And all of those parameters are not only registered by the disk chipset, but they have designated security limits and both parameters and limits can be checked by software who access the disk using the appropriate I/O instructions.

And that software is smartctl, a piece of the smartmontools deb package. Of course, since they access the disk in a raw way, you need to be root to use these commands.

smartctl can ask the disk for its smart identification:
```
# smartctl -i /dev/sda
smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Model Family:     Fujitsu MHV series
Device Model:     FUJITSU MHV2060BH
Serial Number:    NW10T652991F
Firmware Version: 00850028
User Capacity:    60,011,642,880 bytes
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   7
ATA Standard is:  ATA/ATAPI-7 T13 1532D revision 4a
Local Time is:    Mon May 12 02:39:31 2008 CEST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
```
More interesting, smartctl can ask the disk for its parameter values:
```
# smartctl -A /dev/sda
smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000f   100   100   046    Pre-fail  Always       -       124253
  2 Throughput_Performance  0x0004   100   100   000    Old_age   Offline      -       18284544
  3 Spin_Up_Time            0x0003   100   100   025    Pre-fail  Always       -       0
  4 Start_Stop_Count        0x0032   099   099   000    Old_age   Always       -       1199
  5 Reallocated_Sector_Ct   0x0033   100   100   024    Pre-fail  Always       -       8589934592000
  7 Seek_Error_Rate         0x000e   100   087   000    Old_age   Always       -       1761
  8 Seek_Time_Performance   0x0004   100   100   000    Old_age   Offline      -       0
  9 Power_On_Seconds        0x0032   079   079   000    Old_age   Always       -       10866h+57m+47s
 10 Spin_Retry_Count        0x0012   100   100   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       1199
192 Power-Off_Retract_Count 0x0032   099   099   000    Old_age   Always       -       283
193 Load_Cycle_Count        0x0032   100   100   000    Old_age   Always       -       6953
194 Temperature_Celsius     0x0022   100   100   000    Old_age   Always       -       45 (Lifetime Min/Max 14/58)
195 Hardware_ECC_Recovered  0x001a   100   100   000    Old_age   Always       -       62
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       459276288
197 Current_Pending_Sector  0x0012   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0010   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x003e   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x000e   100   082   000    Old_age   Always       -       22371
203 Run_Out_Cancel          0x0002   100   100   000    Old_age   Always       -       1533257648465
240 Head_Flying_Hours       0x003e   200   200   000    Old_age   Always       -       0
```
As you can see, there are some attributes marked as “Pre-fail”. If any of these attributes goes beyond its threshold, the disk is about to fail in hours, maybe minutes.

Even if there are more options to smartctl , the last ones I will comment here are -a and -t.

smartctl -t launches a disk test. It needs a parameter indicating the type of the test, and in the longest case it can last for tens of minutes and will check the electrical and mechanical performance as well as the read performance of the disk, going through all its surface. smartctl -a, in its turn, shows all available information about the disk, including self testing results. Since tests will span minutes or tens of minutes, we can not see them happening. All what we will get when launching tests is like:
```
# smartctl -t long /dev/sda
smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF OFFLINE IMMEDIATE AND SELF-TEST SECTION ===
Sending command: "Execute SMART Extended self-test routine immediately in
off-line mode".
Drive command "Execute SMART Extended self-test routine immediately in
off-line mode" successful.
Testing has begun.
Please wait 41 minutes for test to complete.
Test will complete after Mon May 12 05:44:03 2008

Use smartctl -X to abort test.
```
Here, we’re being informed that (maybe) we will get a slightly lower performance on the disk for the next 41 minutes, since the test has started. It is completely background, or better ‘underground’, since it does not happen under the kernel control at all: everything is happening internally to the disk, and all what we can get is the result.

smartctl -a, in turn, show a very large amount of SMART information about the disk: almost all stored SMART information parsed for us. It is usually better to use a more specific switch, see the man page for details.

Finally, I want to comment that there is a daemon in the smartmontools package, smartd, who can take care of doing tests for you. It works by running smartctl in a periodic way (typically every 30 minutes) and logging all errors and parameter value changes to the syslog. The default configuration in Debian will also mail root if there’s any problem detected. I will not explain here about it, because I want you to read its (short and easy) documentation, but remember that in order to use it you must enable it in /etc/default/smartmontools.

The smartmontools package has been available both in Debian and Ubuntu since a long time ago.
logstalgia: pong-like apache log viewer

Posted: October 5th, 2008, 12:00am CDT by Tincho
Article submitted by Andrew Caudwell

Logstalgia (inspired by glTail) is a website traffic visualization tool that replays or streams Apache access logs as a pong-like battle between the web server and an unrelenting army of requesting hosts. It is rendered using OpenGL, so you’ll need a 3D accelerated video card to run logstalgia.

Requests appear as colored balls (the same color as the host) which travel across the screen to arrive at the requested location. Successful requests are hit by the pong paddle while unsuccessful ones (such as 404s) are missed and pass through.

The paths of requests are summarized within the available space by identifying common path prefixes.

Related paths are grouped together under headings. For instance, by default paths ending in png, gif or jpg are grouped under the heading Images. Paths that don’t match any of the specified groups are lumped together under a Miscellaneous section. Groups can be customized to the page layout of your website fom the command line by specifying a heading, an associated regular expression and a screen percentage.

The simulation can be paused at any time by pressing space. While paused, individual requests can be inspected by passing over them with the mouse.

Logstalgia can read from either a file or standard input. To replay an apache log just run:
```
logstalgia /var/log/apache/access.log
```
You can combine Logstalgia with other tools like tail and ssh to watch the access.log of your web server in real time. eg:
```
ssh user@yourserver.com tail -f /var/log/apache/access.log | logstalgia -
```
Check out a video of Logstalgia in action:

Logstalgia is available in Debian since Lenny and in Ubuntu intrepid. A version of the package for Debian Etch is available on the homepage.
ddclient: getting access to home servers despite having a dynamic IP

Posted: September 28th, 2008, 12:00am CDT by Tincho
Article submitted by Toni Zimmer.

There will be a day when you need access to your Debian box from another place than home, for example to get files from your home server with scp or if you’re running a webserver, an irc proxy, a ftp server, a mail server…

Most likely your ISP gives you a dynamic IP address. This problem can be solved by getting a static DNS name, so you can connect to your home even if your IP keeps changing. First of all you have to create an account with your favourite dyndns provider. I use dyndns.org but there are others, such as [easydns.com], [dslreports.com] or [zoneedit.com]. You can use others if you know ddclient supports its protocol.

There you can specify the hostname (combined with a domain name) for your computer. You can enable mail routing if you want to setup a home mail server.

When you install ddclient you will be asked for the dyndns service provider where you created your account. After that you must enter the complete (or fully qualified) domain name of your computer (something like dpotd.gotdns.org) and your account name (including the password, which will be stored in plaintext in /etc/ddclient.conf!). Now you have to chose the interface that connects you to internet. ddclient will get your IP address from there, so you shouldn’t be behind a NAT. Afterwards you will be asked if you want to start ddclient when connecting with PPP and if you want ddclient to run on system startup or not (probably you will use the first or the second choice). If you choose to run ddclient on startup, you can enter a delay between address checks (default are five minutes, so every five minutes your system will tell your current IP address to your dyndns service provider).

Your settings are stored in /etc/ddclient.conf and look like this:
```
# Configuration file for ddclient generated by debconf
#
# /etc/ddclient.conf

pid=/var/run/ddclient.pid
protocol=dyndns2
use=if, if=eth0
server=members.dyndns.org
login=dyndnsloginname
password='dyndnsloginpassword'
dpotd.gotdns.org
```
If everything is okay, wait a couple of minutes for the DNS information to populate and then you will be able to do something like ssh dpotd.gotdns.org or w3m dpotd.gotdns.org

ddlient is available in Debian since Sarge and in Ubuntu (universe) since Dapper.
mrxvt: Fast, light multitabbed terminal emulator

Posted: September 7th, 2008, 12:00am CDT by Tincho
Article submitted by Hugo Carrer.

As any other Debian user I love writing obscure commands on my terminal. I love too having so many open terminals that I have to come up with a special system to find the one where my favorite obscure command is running on.

To be able to enjoy this I need a very fast multitabbed terminal emulator: mrxvt.

Some of the things I like the most about mrxvt are for example,
- It is very fast and light.
- Fast pseudo-transparency.
- Background with your favorite images.
- Highly configurable keyboard shortcuts.
- You can have the same command typed on every tab at the same time. This feature is disabled by default. you can enable it by editing /etc/mrxvt/mrxvtrc and uncommenting the ToggleBroadcast macro (around line 171). After that, Ctrl+Shift+d toggles input broadcasting to all tabs.
- Automatic or “by-hand” tab labeling.
- It is independent of your desktop (no KDE or GNOME needed).
- Did I mention that is very fast and light?
After installing it would look something like this:

You can change this rather old fashioned look by copying the example config file from
/usr/share/doc/mrxvt-common/examples/mrxvtrc.sample.gz
And placing it in ~/.mrxvtrc

The file is full of comments helping you with the meaning of each option. Of course you can find all available options in the man page. Some useful shortcuts are Ctrl+Shift+t to open a new tab and Ctrl+Shift+m to show the menu.

So, after playing, trying and tweaking for a little while you can get a futuristic look for your terminals. Like this one of me sketching this article on an emacs session inside mrxvt (Note all those beautiful tabs up there)

Downsides? Well it depends on the kind of user,
- No UTF-8 support.
- It has no config menu.
- You have to remember the shortcuts or read the config file every now and then.
- And as with anything worth doing, to get things working the way you want to you’ll have to read through the man page and maybe scratch your head once or twice but it’ll work.
To sum up, it’s the perfect application to config during those boring rainy weekends and then show off to your friends at work.

mrxvt is available in Debian stable and in Ubuntu too.
aria2: high speed command line download utility

Posted: July 16th, 2008, 12:00am CDT by Tincho
Bonus article this week, submitted by Anthony Bryan and Tatsuhiro Tsujikawa.

If you’re a frequent downloader and comfortable on the command line, then you need to try out aria2. aria2 is a cross platform download utility, similar to graphical download managers except that it uses less system resources.

aria2 has a number of invaluable features such as download resuming, BitTorrent and Metalink support, segmented downloading, downloading a single file from one or multiple servers (including integrated BitTorrent and HTTP/FTP transfers), downloading many files at the same time, automatic error recovery/repair (BitTorrent and Metalink downloads only), etc.

aria2 is a command line application, but don’t let that scare you off. You can use aria2fe, a graphical front end, if that makes you more comfortable.

Keep in mind that aria2 is more for heavy downloading, and if you want a webspider then wget would be a better choice.
How to use it
The easiest way to invoke aria2 is by typing aria2c URL/fileName
```
$ aria2c http://host/image.iso
```
The URL can be either a regular URL to a file, a URL to a .torrent file, or a URL to a .metalink file. For BitTorrent and Metalink downloads, there are extra options available such as throttling upload speed, only downloading selected files, changing listening ports, and seed time and ratio. To pause a download, press Ctrl-C. You can resume the transfer by running aria2c with the same argument in the same directory.
Downloading identical files from multiple sources
aria2 supports multiple URLs for the same file. You can specify them on the command line (space separated) and aria2 will download from multiple URLs at the same time.
```
$ aria2c http://host/image.iso http://mirror/image.iso
```
This command will split the download between multiple servers. aria2 can even download the same file from BitTorrent and FTP/HTTP at the same time, while the data downloaded from FTP/HTTP is uploaded to the BitTorrent swarm.
Repairing damaged downloads
aria2 can repair downloads with errors by using the information in .torrent or .metalink files.
```
$ aria2c -M test.metalink --check-integrity=true
```
The -M option specifies a local file called test.metalink to get the information to repair the download.
Parameterized URLs
You can specify set of parts. The following command will download part of the same file from 3 servers, don’t forget to escape the parameter to avoid shell expansion.
```
$ aria2c -P 'http://{host1,host2,host3}/file.iso'
```
You can specify numeric sequence using []. This command will download image000.png through image100.png from the same server.
```
$ aria2c -Z -P 'http://host/image[000-100].png'
```
The -Z option is required if the all URIs don’t point to the same file, such as the above example.
Other options
aria2 has a lot more options, you can for instance use:
- -T filename.torrent to specify a local .torrent file.
- -M filename.metalink to specify a local .metalink file.
- -i textfile will download all the URLs listed in a textfile.
- -s for example -s2 will download a file using 2 connections.
- -j for example -j5 will download 5 files concurrently.
aria2 has many other options. To read the man page, type:
```
$ man aria2c
```
Availability
aria2 is available on most Linux distributions. Official Debian and Ubuntu package are available:
- Debian: stable, testing and unstable
- Ubuntu: feisty, gutsy, and hardy.
Community & developers
aria2 is actively maintained and developed by Tatsuhiro Tsujikawa. Bug reports, feature requests, and forums are found on SourceForge.
Links
email-reminder: Never forget a birthday or an anniversary again!

Posted: July 13th, 2008, 12:00am CDT by Tincho
Article submitted by François Marier. Guess what? We still need you to submit good articles about software you like!

Email-Reminder is a simple tool to define events for which you want to receive a reminder by email. These reminders (sent out daily by a small cronjob) can be either on the day of the event and/or a few days beforehand.

Events can be:
- birthdays
- anniversaries
- weekly, monthly and yearly events
Sample Reminders
Here is an example of what you get in your inbox for an upcoming birthday:
```
From: Email-Reminder
Date: Tue, 12 May 2007 04:00:22 -0400 (EDT)
To: Francois Marier <fmarier@gmail.com>
Subject: Trent Reznor’s birthday

Hi Francois,

I just want to remind you that Trent Reznor is
turning 42 in 5 days.

You can reach Trent Reznor at trent@example.com.

Have a good day!

–
Sent by Email-Reminder
```
And here is one on the day of an anniversary:
```
From: Email-Reminder
Date: Tue, 29 Jul 1996 04:00:11 -0400 (EDT)
To: Francois Marier <fmarier@gmail.com>
Subject: 15th anniversary of Prince Charles and Lady Diana

Hi Francois,

I just want to remind you that the 15th anniversary
(Crystal) of Prince Charles and Lady Diana is today.

Have a good day!

–
Sent by Email-Reminder
```
Event Definition
Events for each user are defined in an XML file (~/email-reminders) in that user’s home directory, click here to see a sample file. You don’t actually have to define each event by hand in the XML file though. Email-Reminder comes with a simple GTK user interface:

Availability
Email-Reminder has been in Debian since Sarge and in Ubuntu since Dapper. It is licensed under the GPL.
More Information
You can find out more about Email-Reminder by visiting its homepage and subscribing to its news feed.

If you want to get involved, see the roadmap and feel free to contribute some patches!
Debian-administration.org on rinetd

Posted: July 2nd, 2008, 6:28pm CDT by Tincho

Unusual non-article ahead:

Debian-administration.org has a nice article about rinetd entitled “Easily forwarding arbitrary TCP connections with rinetd”, go and check it, it is an interesting package I didn’t know about!
zsh: a REALLY nice alternative for bash

Posted: June 18th, 2008, 9:49am CDT by Tincho

Article submitted by Danilo Martins. Guess what? We still need you to submit good articles about software you like!

After years using ZSH instead of BASH, I still don’t understand why isn’t everybody using it. ZSH is a complete shell that will certainly make your life easier. Give it a try.

First of all, you need it installed (duh). APT and its super cow powers will do this for you. You can simply use:

$ sudo apt-get install zsh

and you should be all set. Alternatively, you can install the package “zsh-beta”, but it tends to crash once in a while… ZSH is available on any repository of Debian and Ubuntu.

To try it out, you can simply type zsh, but you wouldn’t be very happy with the result. Let’s personalize it first. First of all, create a file named .zshrc on your home directory. Inside, you should put the text listed here (note: see the commented lines —be sure to try each of them out sometime)

Editor’s note: I’ve moved the sample script to a separate link, to ease cut&paste. Also, note that if you run zsh from Debian testing/unstable for the first time without a .zshrc file, it will greet you with an initial configuration dialog.

Now do run zsh. If you see a different prompt (specially if you did not comment the prompt lines on the .zshrc example above), it’s working. Now, it’s time you see what you can do with this.

First example. Lets suppose you’re doing a long command (cat /etc/mailcap | grep “^audio” | sed s/mplayer/gmplayer) and forget the command syntax for the sed program. You simply move your cursor to the command “sed” and press ALT-H. This should open the man page for sed. After you close the man page, you will automatically be returned with the command you were typing.

Second example. You’re connecting to a remote host using SSH. You remember that you want to use the X11 forwarding, but you don’t remember how to do this. Then, you type “ssh -” and press TAB. Yes, ZSH auto-completes not only files, but also command parameters. Be sure to try it out with whatever command you want to use.

Third example. You have a SSH key to a remote host, and you wish to copy a file from there using SCP. But you do not remember exactly where the file is. You simply type “scp user@remotehost:/home/myuser/myf”, press TAB and watch ZSH doing its amazing trick. Not only ZSH auto-completes files and parameters, but also remote files (remember that for this to work you need to have the RSA/DSA key on the remote host).

Fourth example. You want to install a Debian package (I love this one), but you don’t remember (or are too lazy to) type the whole name of the package. Instead, you simply type “apt-get install mysql-client” and press TAB, and watch ZSH magically auto-completing the package name. If you have more than one, it will list all available below, and if you keep pressing TAB it will complete through each one of them, one at a time. And yes, not only ZSH auto-completes files, parameters and remote files, but it also auto-completes package names. Well, I think we had enough of the “auto-complete” examples, didn’t we?

Fifth example. Yesterday you used a loooooong command and you are too lazy to type it all again. You also do not want to press UP until it appears. Instead of it, you simply type the beginning of the command and try the ALT-P combination. ZSH will auto-complete your command from the history. You can keep using ALT-P and swapping to the previous entries. If you missed it, ALT-N gets you to the next.

Last example. You typed apt-gey install foo bar foo2 bar2 foo3 bar3 foo4 bar4 … foo239 bar239 and pressed ENTER. Oh, shit, apt-gey does not exist. Instead of pressing UP, HOME, going to “gey” and changing it to “get”, you can simply use ^gey^get. This is a shortcut to “repeat the last command, but all occurrences of “gey” are now “get”.

If you liked the way ZSH works and want to use it as your default shell, you can always use the chsh command, and put /usr/bin/zsh there. It’s now your default shell.

Enjoy!
Ghextris: tetris clone with a hexagonal makeover

Posted: June 8th, 2008, 1:58pm CDT by Tincho

Article submitted by Alex Drachmann. Guess what? We still need you to submit good articles about software you like!

The object of the game is much the same as with tetris, only the frame and the falling objects are hexagons. You have to slot the coloured pieces together making rows, which disappear once they are complete, the game ends if the stack of pieces reaches the celling.

Hexagons are hard to stack, so the game is more challenging than other games of its type, but it gets easier with practice. The game play gets rapidly challenging, as you make mistakes or run out of room and to make it worse, the objects you get are often the most useless for the job, plus it seems as if they fall at an increasingly faster rate. A score is kept based on how many lines you complete. Your current score and the highest score can be viewed on the bottom of the window, so you can try to match or beat your best score or that of a friend.

The interface and graphics are simple and integrates nicely in with the gnome environment. The colouring of the pieces is plain, with no texture or shading, so it doesn’t distract away from the game play. The top bar has two entries: play and hepl. The play menu has three actions, «play» (keyboard shortcut: ctrl+n), «pause» (ctrl+p or just p) and «quit» (ctrl+q). The help menu only has the infamous «about» option, with details about the version and author available.

The keys for playing the game are the direction keys, left and right on the keyboard, which moves the pieces left or right. The up and down keys turn the pieces 90 degrees in one direction or the other. Pressing the space bar makes the current piece crash into the slot directly beneath it.

The version I played was version 0.9.0, which is the current version in the universe repositories of Ubuntu Hardy Heron 8.04 and in the Debian repositories. Ghextris is available in all current releases of Debian and Ubuntu.

The official site of the game is: [mjr.iki.fi].

The author of the game and lone developer of it is Mikko Rauhala, who admits to being inspired by a similar game called Xhextris by David Markley.
JOE Joe’s own editor: a really usable text editor

Posted: June 2nd, 2008, 2:49am CDT by Tincho

Article submitted by Neil Stewart. Guess what? We still need you to submit good articles about software you like!

Back in the day, when I was new to Linux, joe was the first text editor that I managed to quit without having to reboot my machine. That I am still using it today, many years later, goes to show just how simple yet powerful joe is. If you don’t want to use emacs (because what’s the point of running two operating systems?) and still can’t work out how to use vi, then joe is for you.

joe is started from the command line with joe or joe filename to edit filename. When you start joe you get a single header bar with information about where the cursor is, what time it is and, crucially, the message «Crtl-K H for help» (^KH in joe shorthand). So if you press Ctrl and K together, release them, and then press and release H, the top half of the screen is given over to a brief list of commands. And it’s here I learnt how to quit (without rebooting), how to open a new file, how to save a file. And how to move the cursor around, how to find and replace, how to skip over words and lines, how to marks blocks of text and move them about. And you can carry on working on your file —you just type— with the help up. So within a really short amount of time you’ll be up to speed.

But joe is powerful too. For example, you can process any block of text through any shell command. joe’s help file gives a good example. If you mark the block of text by moving the cursor to the beginning and ^KB, then move to the end and ^KK, then pipe the block of text through sort with ^K/ sort. joe then runs the block of text through sort and replaces the block with the result. Powerful, especially in conjunction with old faithfuls like tr and sed.

Search and replace is also easy. ^KF and enter a search term. That’s it. But search and replace is powerful too. You can reuse old search terms by pressing the up cursor key, including terms from previous sessions. You can use tab completion to complete from any of the words in your current document after you’ve typed the first few letters. Then you can choose what to do when you find it. To replace press R and enter the replace term. You can replace one by one, or replace all. ^L finds the next entry. And you can use regular expressions —this is unix after all. Again the help file has a neat example. If you search for \*,\*,\*$ (\* matches zero or more characters and $ matches the end of a line) and replace with \2,\1, (\X matches Xth pattern found) the string «one,two,three» becomes «three,two,one». Bring up help with ^KH and skip a few screens with ^[. a few times to remind yourself of the regular expressions.

Macros are easy too. Start recording one of ten macros with ^K[ and then a digit. Finish the macro with ^K]. Then use ^Kdigit to play the macro.

joe has many more features. joe remembers where it was in the file when you next edit it. joe colours your C, Java, LaTeX, HTML, and many other formats by default. joe indents your source code and justifies your text. joe supports multiple windows. joe can set bookmarks. You can compile your source code from within joe (^[C) and then skip to the errors the compiler identifies (^C= next error, ^C- previous error).

Finally, joe is old, stable, and just works. It’s in version 3.5 in etch and lenny. I use it for everything, all day every day, and it never fails. Find out much more with info joe or at the Sourceforge home page.
mhddfs: join several real filesystems together to form a single larger one

Posted: May 25th, 2008, 12:00am CDT by Tincho
Article submitted by Roman Mamedov. Guess what? We still need you to submit good articles about software you like!

Suppose, you have three hard drives - sized 80, 40 and 60 GB. And 150 GB of music files, which you need to store on these drives. How would you do it?

The two solutions I knew of, were:
- either to simply have three separate «Music» folders - one per each drive;
- or create some sort of RAID, joining all the drives into an array.
However, the first method is quite tiresome, as one needs to decide how to split the data between the drives and keep track of what is stored where. For example, I might decide to store all «Classical» music on the first disk, and «Rock» music on the second. Then, suddenly, the first drive fills up and the second one still has plenty of space. Now I need to move the files between the disks, or jump around with symlinks.

The RAID method, while solving this problem, always incurs significant loss of either storage reliability or usable disk space.

But recently, I found a better solution to this problem and similar ones: mhddfs. It is a FUSE filesystem module which allows to combine several smaller filesystems into one big «virtual» one, which will contain all the files from all its members, and all their free space. Even better, unlike other similar modules (unionfs?), this one does not limit the ability to add new files on the combined filesystem and intelligently manages, where those files will be placed.

The package is called «mhddfs» and is currently present in Debian Testing and Unstable. It does not seem to be available in Ubuntu at the moment.

Let's say the three hard drives you have are mounted at /mnt/hdd1 /mnt/hdd2 and /mnt/hdd3. Then, you might have something akin to the following:
```
$ df -h
Filesystem            Size  Used Avail Use% Mounted on
...
/dev/sda1              80G   50G   30G  63% /mnt/hdd1
/dev/sdb1              40G   35G    5G  88% /mnt/hdd2
/dev/sdc1              60G   10G   50G  17% /mnt/hdd3
```
After you have installed the mhddfs package using your favourite package manager, you can create a new mount point, let's call it /mnt/virtual, which will join all these drives together for you. The beauty of FUSE means you don't really have to be root for this (can be just a member of the fuse group), but for the sake of examples' simplicity, let's suppose we are logged in as root here.
```
# mkdir /mnt/virtual
# mhddfs /mnt/hdd1,/mnt/hdd2,/mnt/hdd3 /mnt/virtual -o allow_other
option: allow_other (1)
mhddfs: directory '/mnt/hdd1' added to list
mhddfs: directory '/mnt/hdd2' added to list
mhddfs: directory '/mnt/hdd3' added to list
mhddfs: move size limit 4294967296 bytes
mhddfs: mount point '/mnt/virtual'
```
The «-o allow_other» option here means that the resulting filesystem should be visible to all users, not just to the one who created it.

The result will look like this:
```
$ df -h
Filesystem            Size  Used Avail Use% Mounted on
...
/dev/sda1              80G   50G   30G  63% /mnt/hdd1
/dev/sdb1              40G   35G    5G  88% /mnt/hdd2
/dev/sdc1              60G   10G   50G  17% /mnt/hdd3
mhddfs                180G   95G   85G  53% /mnt/virtual
```
As you can see, the new filesystem has been created. It joined the total size of all drives together (180G), added together the space used by all files there (95G) and summed up the free space (85G). If you look at files in /mnt/virtual, you'll notice that it has files from all three drives, with all three directory structures «overlayed» onto each other.

But what if you try to add new files somewhere inside that /mnt/virtual? Well, that is quite tricky issue, and I must say the author of mhddfs solved it very well. When you create a new file in the virtual filesystem, mhddfs will look at the free space, which remains on each of the drives. If the first drive has enough free space, the file will be created on that first drive. Otherwise, if that drive is low on space (has less than specified by «mlimit» option of mhddfs, which defaults to 4 GB), the second drive will be used instead. If that drive is low on space too, the third drive will be used. If each drive individually has less than mlimit free space, the drive with the most free space will be chosen for new files.

It's even more than that; if a certain drive runs out of free space in the middle of a write (suppose, you tried to create a very large file on it), the write process will not fail; mhddfs will simply transfer the already written data to another drive (which has more space available) and continue the write there. All this completely transparently for to the application which writes the file (it will not even know that anything happened).

Now you can simply work with files in /mnt/virtual, not caring about what is being read from which disk, etc. Also, the convenience of having large «contiguous» free space means you can simply drop any new files into that folder and (as long as there's space on at least one member of the virtual FS) not care about which file gets stored where.

If you decide to make that mount point creating automatically for you on each boot, you can add the following line to /etc/fstab:
```
mhddfs#/mnt/hdd1,/mnt/hdd2,/mnt/hdd3 /mnt/virtual fuse defaults,allow_other 0 0
```
For more details, see man mhddfs.

The last, but not the least important thing to mention, is the fact that it's very simple to stop using mhddfs, if you later decide to do so - and not lose any file data or directory structure. Let's say, at some point in time, you purchase a new 500 GB hard disk, and want to sell the smaller disks on Ebay. You can just plug in the new drive, copy everything from /mnt/virtual onto it, and then remove mhddfs mount point and disconnect old drives. All your folders, which were previously merged in a «virtual» way by mhddfs, will now be merged in reality, on the new disk. And thanks to the fact that files themselves are not split into bits which are stored on different drives, even in the unlikely event when mhddfs suddenly no longer works for you (or disappears from existence), you can still copy all your data from all three drives into one single folder, and have the same structure you previously had in that /mnt/virtual mount point.
potrace: Transform bitmap images into vector graphics

Posted: May 19th, 2008, 12:00am CDT by Tincho
Article submitted by András Horváth. Guess what? We still need you to submit good articles about software you like!

You can face the task sometimes that you need a high resolution material from a particular image. Most probably when you’re a graphic designer (or even a tattoo artist), you might want to have a good quality result from a low resolution image that you can magnify no matter how much, it will give you smooth edges in high quality.

For this, you have the following possibility without a trace program: using a pixel graphic software like Gimp, you can resize the image with the best resampling method and apply a selective blur filter on it. Most of the times this doesn’t give the necessary quality.

There is a small but powerful utility called potrace developed by Peter Selinger, a mathematics professor at the Dalhousie University.

With a trace program like potrace, all you have to do is to give the image as an input, and there you have the result in the standard SVG format. potrace can produce even PDF format as an output.

Command-line example:
```
$ potrace -s image.bmp
```
With this process, the program transforms the images’ pixels into filled curves that have infinite resolution with smooth lines at any zoom.

In my personal experience while working as a graphic designer, potrace gave me very good results to many input images. Compared to other high expensive proprietary software, when the input image had sharp endings, potrace gave sharp edges in the result and other programs gave bad results, curving the edges. That needed a lot of manual correction.

Pros (compared to other programs):
- Very good results
- Pretty fast
- Can be easily run from a command-line
- Can be used from the Inkscape open-source vector graphics software (Path / Trace Bitmap menu or Shift+Alt+B)
Cons:
- Only 2 colors output (Black & White), no colored process is available yet
- potrace does not support PNG images as an input (though images can be converted easily from PNG with a whole variety of free programs)
This is an example found in the homepage, you can see the original bitmap and the vectorised image:

The package has been available both in Debian and Ubuntu since a long time ago.

Related links:

[en.wikipedia.org]

[wiki.inkscape.org]
cu: Simple serial communication program

Posted: May 4th, 2008, 12:00am CDT by Tincho
Article submitted by Floris Bruynooghe. Guess what? We still need you to submit good articles about software you like!

If you have servers, embedded systems or high end routers (or old PC’s doing those jobs) chances are that they will have a console on a serial port instead of being equipped with a display and keyboard. Even when normally you use ssh(1) or similar to log in to those machines, in debugging and rescue sessions you often want to see console messages, pull down the network interface or maybe play with the boot loader (like launching alternate kernels from within grub). You then need a null modem cable (often supplied by vendors when they use RJ45 plugs for the serial console instead of RS232) to connect the serial port of your computer to the serial console of the device.

Now you also need a program, often called a “serial communications” program, that can connect to your serial port and allow you to use your terminal as the console of the attached device. Most serial communication programs however where actually made in an era when most networking happened by using a modem —attached to the serial port— to dial up other systems. As a result of this they tend to have very heavy and bloated interfaces, giving you all sort of modem-specific functionality via a complicated interactive interface. This is where cu comes in! It is a very simple version of it: a simple command line program doing the bare minimum needed.

In it’s simplest scenario, described above, invocation is trivial:
```
$ cu -l /dev/ttyS0
```
For example this is how I connect to my home router (normally I’d use apt-get over ssh though):
```
flub@laurie:~$ cu -l /dev/ttyS1
Connected.

Debian GNU/Linux 4.0 balder ttyS0

balder login: root
Password:
Last login: Sun Apr 13 19:58:46 2008 on ttyS0
balder:~# apt-get update
...
balder:~# apt-get upgrade
...
balder:~# logout

Debian GNU/Linux 4.0 balder ttyS0

balder login: ~.
Disconnected.
flub@laurie:~$ 
```
As you can see here I used the seconds serial port (ttyS1) of my local machine (laurie) to connect to the first serial port (ttyS0) of the router (balder), which is configured to run a getty on it. This allows me to log in and do any task I want just like from any other terminal. Disconnecting is done just as in ssh by default: by typing `~.‘ just after you have typed a newline.

The above will connect you to the serial line configured as 9600, 8n1 (9600 baud rate, 8 data bits, no parity, 1 stop bit). This is most likely the default setting on the device. However as this is sometimes a little slow you might want to configure your server (or whatever the device is) to use a faster baud rate, or maybe your vendor did that already and told you in their documentation what speed to use. The speed is easily changed by another command line switch:
```
$ cu -l /dev/ttyS0 -s 150000
```
If you need to change the parity this can be achieved by using -e for even and -o for odd parity. The stop bits and data bits can’t be changed by command line switches unfortunately, but needing them seems very rare.

cu does have a fair few more options and some more commands starting with the `~‘ escape character. Most of these have to do with using modems to dial other systems however and are not applicable for null modem use. The manual page, cu(1), gives a detailed description of more advanced features.

(1) If you’re unlucky enough to not have a serial port anymore, like many modern laptops, a USB-dongle with a serial port is usually assigned to /dev/ttyUSB0.