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The Mailbag From The Readers of Linux Gazette

• compressed tape backups
• Daemon vs CGI spawning processes
• Compiling qt 3 lib
• VP and net load equation

compressed tape backups

Hi TAG's,

quite a while back I remember a discussion on compressed tar archives on tape and the security risk, i.e. the data would be unrecoverable behind the first damaged bit.

Now at that time I knew that bzip2, unlike gzip, is internally a blocking algorithm and it should be possible to recover all undamaged blocks after the damaged one.

Test RESULTS:

tar archive of 90MB mails, various size, mostly small

tar -cvjf ARCHIVE.tar.bz2

bvi to damage the file at about 1/3 (just changing a few bytes)

tar -xvjf ARCHIVE.tar.bz2

produces an error and refuses to continue after the damage. --ignore-failed-read doesn't help at all, neither -i

running bzip2recover produces a set of files rec00xxFILE.tar.bz2 decompressing them individually and cat all good ones into tar:

tar produces an error where the data are suddenly missing, skipping to next file header, but it's not recovering anything beyond the error. It seems it's unable to locate the next file header and simply skips through the remaining file. I also tried to run tar on the decompressed blocks after the error only -- same result: It's skipping till next file header, doesn't find one and ends with an error.

In my tar "tar (GNU tar) 1.13.18" I discovered the following option (man page):

--block-compress

this option is non-existent in "tar --help" and running:

tar -cvzf ARCHIVE.tar.gz --block-copmress

says:

tar: Obsolete option, now implied by --blocking-factor

Writing archives with --block-copmress and/or --blocking-factor 2[0] does not improve things very much. several times with gzip and a blcoking of 2, i.e. 1kB), I was lucky and the error was in one large mail (attachement). In that case tar was able to locate the next file header and I lost only the one damaged mail. I introduced some more damaged blocks and suddenly tar was skimming through the remaining tar-file again without recovering any more files.

Fazit:

- seems still to be highly risky to use compression on tapes archives

- blocking improves chances -> use a very small blocksize.

One question remains: Can some flag improve the tar behaviour in locating the next file header? I couldn't find one in either tar --help nor the man page.

I also start wondering what tar says to several unreadable tape blocks and how it's going to locate the next file headers after that.

I'm ordering the head cleaning tape I think....

K.-H.

Daemon vs CGI spawning processes

Dear all,

recently, I switched from using CGI to run a program to using the SOAP-Lite 0.55 XML-RPC Daemon to run the same program.

The only noticeable difference between using the two, is that using CGI, the web page reloaded straight away, but with the new daemon, the web page waits for the program to finish before reloading.

I have no idea about CGI and perl daemons, so I'm writing to this list to ask about processes. It seems to me that the Httpd daemon (Apache2) will spawn it's own CGI process that handles the program independently, whilst the self-created daemon doesnt.

Im posting the daemon's code below if it helps.

See attached soap-daemon.Seaver.pl.txt

Compiling qt 3 lib

I'm wondering if someone might have an idea about what's going wrong with my effort to compile ver 3 of the qt lib. I DL'd the source and unpacked to a dir under my user normal user's home dir, and ran configure with a few options specified. It completed normally w/o error. But when I run make from the same dir, it errors out immediately:

Insp8000:~/Builds/qt-x11-free-3.1.2 > make

make[1]: Entering directory `/home/jkarns/Builds/qt-x11-free-3.1.2'
cd qmake && make
/bin/sh: cd: qmake: No such file or directory
make[1]: *** [src-qmake] Error 1

I should mention that I didn't intend to address the question so much toward qt explicitly, but rather I'm wondering if the problem might be due to peculariarities of gmake, or some other system configuration issue - I guess I'll look into updating gmake on this machine. I've run into similar problems when compiling other pkgs, although most pkgs compile w/o a problem.

VP and net load equation

Hello,

Is it possible in a VPN based network. To get distribution of Net load on the side of the Linux servers so that each Client get (the client conect thru a VPN Tunnel through a Wierless Network) the same speed in the Internetconection


Best regard
Bernhard Schneider

• Linux Gazette entry in Wikipedia
• Home Network Internet Connection Sharing
• I read your "How to Create a New Linux Distribution: Why?"

Linux Gazette entry in Wikipedia

I've added a stubby entry to Wikipedia (http://www.wikipedia.org/wiki/Linux_Gazette). Anyone care to expand on it?

[Jason] Hmmm....are you sure the wikipedia folks like that sort of thing?

http://www.wikipedia.org/wiki/Wikipedia_is_not_a_dictionary

Yeah, I think it's OK. I've gone more for encyclopaedic information than a mere definition, even if it is a stub. Starting a stub is encouraged - an extreme version of how a stub can grow from a definition (from FOLDOC) is here http://www.wikipedia.org/w/wiki.phtml?title=PS/2&action=history - in the space of one hour it changed completely, and grew to about 4 times the original size.

Anyway, I cite precedence http://www.wikipedia.org/wiki/Macworld

Home Network Internet Connection Sharing

Hi,

Thanks for you generous help. You must be very good-hearted people.

[Thomas] Yes, we are

[Ben] Thank you for the compliment, doctor. We're all here for a number of reasons, but I have to agree with you to this extent: everyone who has stayed with The Gang over the long term has earned my respect for their demonstrated willingness to give their time to this endeavor. If you believe, as I do, that Linux is improving the world by reducing the amount of chaos in the world of computers, then all of us have contributed to making this world a better place.

I think I have identified an area of need: I have used RHL for years, and am now getting a few machines around the place for different uses including software and hardware testing. I'd like to set up a network at home, which I am finding very difficult because my USB port has taken over my eth0 and the configuration tools won't let me save anything...

[Ben] Could you clarify that, please? eth0 is an Ethernet network interface; USB is a completely separate physical entity that, as far as I know, shares almost nothing with it. I would suggest that you carefully read "Asking Questions of The Answer Gang" at

<http://www.linuxgazette.net/tag/ask-the-gang.html>;

particularly the part about "Provide enough, but not too much information". Simon Tatham's page, linked there, is a really good guide to effective bug reporting and following it will benefit you when asking questions in technical fora.

[Thomas] How do you mean "taken-over"? Indeed, USB and "eth0" (which I'm transliterating to meaning your NIC (Network Interface Card) should be two separate issues (that is unless your NIC is USB based, which is obsured.....).

But the real area of need I think is sharing an internet connection. In Australia we have cable modems and ASDL as well as dial up modems, and I noticed Mandrake just has a button for this! RHL is much more terse.

[Thomas] Tut, tut -- what you are describing here is a difference in the GUI configurations of the two different distributions, essentially the underlying information about each network IP, interface, etc, is stored in the same configuration files in "/etc"

[Ben] Linux is based on understanding the underlying mechanisms rather than just "pushing the button" - whatever buttons may exist in specific distros. The process of sharing a net connection is not a difficult one, and is domented in the Masquerading-Simple-HOWTO, available at the Linux Documentation Project <http://www.tldp.org/>;. Read it and understand it, and you'll find that sharing a Net connection is very easy indeed.

I'll copy this to RHL, too, so they know the difficulties I'm having.

[Thomas] I wouldn't bother -- RH are most likely not concerned with helping you setup your network.

On the contrary, if changing something minimal about their installer would win them a few people more from one of the other distros, they might be inclined to make that easier. Also, if they never hear complaints they have to assume it's all good, right? -- Heather

It is hard to find authoritative info about this.

Thank you again,

Julian

[Ben] Not really. The Answer Gang's Knowledge Base containg this information; searches of the Net (I use Google but any search engine will find this) will come up with hundreds of thousands of hits. The trick is to search for knowledge on the topic rather than a button to push.

[Thomas] Your question is extremely loose -- what exactly do you want, what type of network? I only use PLIP, but that is only because I don't have any NIC's at the moment.... I suspect that this approach in networking is not what you want.

Please take a look through the past issues of the linux gazette - we have a search engine at the main site:

http://www.linuxgazette.net

and especially though the knowledge base (above).

When you can refine your question a little more, please let us know

I read your "How to Create a New Linux Distribution: Why?"

This was a TAG thread in issue 39, quite a long time ago. The number of distros has increased drastically, but the need to ask "Why?" before sprouting a new one hasn't changed - in fact, if anything, it's gotten more important than ever... -- Heather

I have a similar idea. However, I don't know if I would go as far as calling it a distribution. All I want is to semi-duplicate an environment I have set up.

I would like to somehow create an installable version of my slackware system. Not a ghost but one where you can alter partitions and select (auto select) nic, MB-features etc, upon installation.

[Thomas] Installable version??? Hmmm, how do you mean? My first ever distribution I used was slackware 2.0, and that was installable. I disgaree with your methods. Tweaking partitions upon installation is perhaps fatalistic, especially if you don't know what you're doing. And in anycase, what is it that you're trying to achieve? I'd have said that most Linux distro's do a damn good job at installing Linux.

I'd be inclined to use a chroot first so that you can test it before you go live. Unfortunately, I don't have enough experience / knowledge to provide you with that. Heather Stern may well pipe up, I know that she does exactly that all the time, using chroot.

Yes - I either set aside a whole partition (for a "one big slash" installation of the given type) or prepare a file and format it as ext2 (for loopback mounting) then only mount the given environment when I need it. Compressed instances of the loopback version can serve as nice backups or baselines for fresh installs on a lab system. I often make a point of leaving bootloader code out of them, though; something I need to back in when preparing those same lab boxen. -- Heather

Do you know a good way to do this or maybe just some pointer on where and how I should get started?

Many thanks if you take the time to answer this.

Best regards - Jon

Ps. Do I need to subscribe to receive the answer? Ds.

[Thomas] Nope, by common courtesy, we always CC the querent (that's you).

Sending people their reply directly, they get it right away, and it's nice that they can see their answer even if their thread doesn't make it into the magazine.

I believ the set of scripts called YARD aims at being something like what you want; visit Freshmeat.Net to look it up. YARD stands for "yet another rescue disc" and is about rescuing the specific system in front of you, instead of just being a general case utility disc like Tom's Rtbt, LNX-BBC, superrescue, etc. -- Heather

[Kapil] You should take a look at mindi which tries to create a distribution out of an existing installation. It runs from a Live CD but can also be installed so that takes care of your "partitioning" issue (perhaps you need "mondo" to actually install your home dirs and so on). To handle hardware detection such as nic,video etc. you must install "discover" or "kudzu" and after that (As far as I can see) you are on your own.

• Liunx Gazette in Palm Format
• Your web site

Liunx Gazette in Palm Format

First off I'd like to say that the magazine is excellent, I've only just come across it. I've been using Linux for around 5 years and there are still some good hints and tips to be found!. Just a suggestion but any possibility of a plucker version of your mag? I read alot on my palm and this would be most useful, I have found that the downloadable HTML version of each mag has links in the contents page that don't resolve within the document but to seperate files on the server thus making conversion awkward i.e the contents page links don't resolve

James Herbert Senior Software Engineer

[Mike] I assume you mean TWDT.html in each issue. Yes, we can assemble it using a custom TOC page with internal links. It may take a couple months till we get around to it though.

The way it's put together is by merging the fragment articles and columns along some fairly plain "startcut"/"endcut" blocks in the templates ... except for The Answer Gang, where I provide a TWDT edition for the back end.

But to solve his actual problem, he really wants to check out Sitescooper (www.sitescooper.org) and pick up the regularly prepared scoop of the LG issue. I hope they keep 'em up to date. It occurs to me that maybe we should list them on the mirrors page. That's http://scoops.sitescooper.org and it's available in 3 different Palm friendly formats. Plus sitescooper is open source - just download and have fun Even flavors for MacOS and Windows users, though it's worth noting you need a working copy of perl. -- Heather

[Mike] If there's anything else required to put it into Palm format, send us a HOWTO if there's one available. However, that might work better as a script on your end that downloads the issue (perhaps the FTP file) and converts it to plucker format, whatever that is. Since we have so many versions of the same thing already (web files, FTP tarball, TWDT, TWDT.txt), and only a few readers have Palms.

[Ben] You can use "bibelot" (available on Freshmeat, IIRC); it's a Perl script that converts plaintext into Palm's PDB format. I have a little script that I use for it:

See attached pdbconv.bash.txt

This uses the textfile name (sans extension) for the new file name and the PDB internal title, and does the right thing WRT line wrapping. Converting the TWDT would require a single invocation.

Does the raw PDB format have a size limit? Our issues can get pretty big sometimes... -- Heather

Your web site

Hi

I've been an LG reader for 5 years now, and a year (or maybe more) ago you changed the web site. I really preferred the old site. Why?

Hmmmm it's hard to place a finger on it. One definite thing I miss is that I used to love having the really big index, which would show you a huge table of contents, with the table of contents of every issue listed.

[Mike] That is still around, but it's called "site map" now. There's a link on the home page, or bookmark the direct URL:

http://www.linuxgazette.net/lg_index.html

I'm blind and use a screen reader, and I could use my screen reader's search facility to find topics -- if I wanted to know about ncurses, I just search for that, and would hear the latest article which had ncurses in the title. Pressing a single key again and again would take me to all articles with ncurses, for example, in the title. Can this be reintroduced? I know the search feature does something similar, but I still think it makes it harder (for me) to find what I want. That's the main thing I can think of right now, but I'll keep you informed if I thik of the other little things.

But with regards to the content of the magazine - it's excellent, and the archives are a wonderful resource.

Saqib Shaikh

[Thomas] You're quite welcome