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Thursday, February 7, 2002TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
E\*Trade Moves to Linux Servers
Not Quite Top 40, but...
Solaris 9: Major Advance
GNOME and .NET? Say it Ain't So!3) Linux Resources
How To Create The Favorite Icon
Beginner's Guide to Armoring Linux
Solaris NIS+ FAQ
Automate Command Line FTP
IPv6 For Linux4) App o’ the Week
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1) Sean’s Notes
Unix, as you may have observed, heavily promotes the sharing of source code. Its command line interface also lends itself to plain text-based documents. Thus, it should be no surprise that Unix has a rich set of text processing commands.
One of the more useful utilities is the diff and patch combination. “diff” returns the difference between a set of files (confusingly referred to as a “diff”), and patch applies the changes specified in the diff to a file or files.
Programmers, authors, and web programmers love this. If you’ve got 5,000 lines of text, and change three lines, you can produce a diff of perhaps only a dozen lines. This diff can be sent around and applied with patch. Not only does it save space, but the diffs themselves are easily read so the changes stand out. Another situation, where two people make changes in different parts of the document, is also handled with diff/patch. Both diffs can be applied, and the document is current. If each person were to send out copies of their modified document, there is no way to tell which is current.
From /tmp, I’m going to make a two copies of my services file:
$ cp /etc/services test.orig $ cp /etc/services test
(the services file lists the port->service mappings, such as TCP port 25 is SMTP. A very handy reference)
Then, I’ll make a change to test by adding a line to the end:
$ echo “sometest 1234/tcp #testing” » test
And then I’ll run diff:
$ diff test.orig test 512a513
sometest 1234/tcp #testing
When using diff and patch, remember that the original file goes first, and the new file goes second (in the case of diff).
The ’>’ symbol tells me that a line was added, and the numbers above say that it was at line 513. The problem with this type of diff is that there is no context, just an instruction to add in a new line. The unified diff format takes care of this, and a few more problems:
$ diff -u test.orig test — test.orig Wed Feb 6 18:34:38 2002 +++ test Wed Feb 6 18:39:29 2002 @@ -510,3 +510,4 @@
# Local services test 34343/tcp #test +sometest 1234/tcp #testing
Here you can see that some of the text surrounding the change has been included. Thus, multiple patches can be applied to the same file without a great worry of collision. The unified diff format isn’t perfect, though. Sometimes, especially in source code, you may have to make a couple of the patches by hand, because the amount of context included wasn’t enough for patch to figure out where it should be.
I’m going to run that last one into a file, which I’ll call test.diff:
$ diff -u test.orig test > test.diff
test.diff is what I’d distribute as my diff, had I needed to send around this patch.
Now, I’d like to patch test.orig to be at the same level as test:
$ patch test.orig test.diff patching file test.orig
The easiest use of patch is to pass it the file name, and then the name of the diff. I can verify that it worked by comparing test.orig and test:
$ diff test.orig test $
In the real world, you may have multiple files, with multiple directories. The unified format handles this nicely, packaging all the patches into one directory:
$ diff -uNr directory.orig directory.changed > difffile
-N tells diff to recognize the creation of new files in directory.changed, and -r specifies that it should descend into directories recursively.
With a big patch file like difffile, I can send it directly to patch with:
$ patch -p0 < difffile
Note the direction of the arrow this time. We’re sending the contents of difffile to the standard input of patch. We could have also done the same thing with
$ cat difffile | patch -p0
What’s -p0 do, though? Recall that we executed diff from the directory above “directory.changed”. Thus, if we’re reflecting a change in a file called README, it’s actually directory.changed/README within the diff. To apply the patch, we must also be in the same directory relative to our unpatched code. The -p option tells patch how many directories to strip off the top (in this case, none). Had we been in directory.orig, we’d need -p1. You can usually tell that you’re in the wrong directory (or need to play with the values of -p) if you see the following:
$ patch -p0 < /tmp/test.diff can’t find file to patch at input line 3 Perhaps you should have used the -p or –strip option?
The text leading up to this was:
|— test.orig Wed Feb 6 18:34:38 2002
| +++ test Wed Feb 6 18:39:29 2002 |
|---|
File to patch:
Hit ^C (control-C) to abort, and fix your directory problem.
Diff and patch are easy and efficient ways of sending out changes to source code, or almost any type of document. Being able to patch will save you time downloading kernel updates for sure! If you’ve ever made a contribution to an Open Source project (even if it’s just correcting some spelling, or fixing documentation), the project team will surely appreciate your contribution in the form of a unified diff.
Long live the Penguin,
Sean mailto:swalberg@cramsession.com
2) Linux News
E*Trade Moves to Linux Servers
“The online brokerage is moving its computer systems over to IBM servers that run the operating system. In a statement, E*Trade cited cost savings and performance as reasons for switching to Linux.” This is the first I’ve heard of someone in the financial sector doing this!
http://www.newswire.ca/releases/January2002/31/c7527.html
Not Quite Top 40, but…
This online radio station (and on air, in some locations) is going to read the Linux source code on the air. All of it. I couldn’t seem to get a connection when I tried, but out of curiosity I’ll continue to try to give it a whirl.
http://radioqualia.va.com.au/freeradiolinux/
Solaris 9: Major Advance
This news report tells of some of the features we can expect to see in Solaris 9. SSH and Kerberos are now standard, plus difficult-to-secure applications like telnet and NFS can be left out of the install. Besides a lot of new enhancements, Solaris 9 is supposed to have Linux-compatibility features. GNOME has been left out of this one, but it’s supposed to be an add-on.
http://www.eweek.com/article/0,3658,s%253D701%2526a%253D21767,00.as p
GNOME and .NET? Say it Ain’t So!
GNOME leader Miguel de Icaza says that GNOME will start to use Microsoft’s .NET in the future. I’m no expert on .NET, but I’m still pretty skeptical.
http://theregister.co.uk/content/4/23919.html
3) Linux Resources
How To Create The Favorite Icon
Until Mozilla started supporting the “favorite icon” feature, I ignored it. Basically, Internet Explorer tries to download a file called “/favicon.ico” from every website you hit. If a file is returned, it’s used next to the site’s name in the Favorites menu. Here’s how to create a “favorite icon” using the GNU tools.
http://www.mavetju.org/unix/favicon.php
Beginner’s Guide to Armoring Linux
Lance Spitzner is a big name in Unix security. Here are his guidelines for securing Linux servers that want to play on the Internet. Though this document is somewhat dated, all of the concepts are sound.
http://www.enteract.com/~lspitz/linux.html
Solaris NIS+ FAQ
NIS+ is a way of synchronizing passwords between Solaris servers, and to a limited extent, Linux servers. If you’re the one responsible for the NIS+ server, this FAQ will be right up your alley. I can’t count the number of times I referred to it when I was in that role.
http://www.eng.auburn.edu/users/rayh/solaris/NIS+_FAQ.html
Automate Command Line FTP
The command line client for FTP is more powerful than you might think. From the .netrc file, you can have it login to sites for you, and execute frequently-used command sequences. This page has a description of what can be done, along with several examples.
http://www.mavetju.org/unix/netrc.php
IPv6 For Linux
Linux has supported IPv6, the next generation Internet Protocol, for some time now. The Internet doesn’t support it as a whole, so you have to tunnel it. This site, based in Canada, allows you to join a global tunnel, and get started into IPv6.
http://www.freenet6.net/
4) App o’ the week
You’re probably familiar with filename completion in the shell… Hit tab, and you get a list of all the filenames that begin with what you’ve typed so far. If there is only one, it finishes it off for you. But wouldn’t it be great if this extended to other programs? Type “ssh TAB” and you get a list of all the hosts you regularly SSH to? Or pull up a list of NFS shares when you type in a hostname? Here you go.
http://www.caliban.org/bash/index.shtml#completion
(C) 2002 BrainBuzz.com, Inc. All Rights Reserved.
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