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neysx 05/08/21 22:23:44 |
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|
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Added: xml/htdocs/doc/en/articles afig-ct-ext3-intro.xml |
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prompt-magic.xml |
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Log: |
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#103211 & #101920, GuideXMLified articles |
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|
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Revision Changes Path |
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1.1 xml/htdocs/doc/en/articles/afig-ct-ext3-intro.xml |
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|
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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/afig-ct-ext3-intro.xml?rev=1.1&content-type=text/x-cvsweb-markup&cvsroot=gentoo |
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plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/afig-ct-ext3-intro.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo |
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|
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Index: afig-ct-ext3-intro.xml |
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=================================================================== |
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<?xml version='1.0' encoding='UTF-8'?> |
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> |
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|
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<guide link="/doc/en/articles/afig-p7.xml"> |
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|
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<title>Advanced Filesystem Implementor's Guide : Introducing ext3</title> |
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|
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<author title="Author"> |
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<mail link="drobbins@g.o">Daniel Robbins</mail> |
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</author> |
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<author title="Editor"> |
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<mail link=" dhaskew@×××××××××.net">David H. Askew</mail> |
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</author> |
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|
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<!-- The original version of this article was first published on IBM |
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developerWorks, and is property of Westtech Information Services. This |
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document is an updated version of the original article, and contains |
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various improvements made by the Gentoo Linux Documentation team --> |
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|
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<abstract> |
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With the 2.4 release of Linux come a host of new filesystem possibilities, |
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including Reiserfs, XFS, GFS, and others. These filesystems sound cool, but |
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what exactly can they do, what are they good at, and exactly how do you go |
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about safely using them in a production Linux environment? Daniel Robbins |
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answers these questions by showing you how to set up these new advanced |
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filesystems under Linux 2.4. In this installment, Daniel takes a look at ext3, |
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a new improved version of ext2 with journaling capabilities. |
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</abstract> |
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|
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<version>1.0</version> |
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<date>2005-08-13</date> |
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|
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<chapter> |
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<title>Introduction</title> |
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<section> |
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<body> |
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|
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<note> |
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The original version of this article was first published on IBM developerWorks, |
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and is property of Westtech Information Services. This document is an updated |
| 56 |
version of the original article, and contains various improvements made by the |
| 57 |
Gentoo Linux Documentation team. |
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</note> |
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|
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<p> |
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In the past few installments, we've taken a bit of a detour by looking at |
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non-traditional filesystems such as tmpfs and devfs. Now, it's time to get back |
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to disk-based filesystems, and we do this by taking a look at ext3. The ext3 |
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filesystem, designed by Dr. Stephen Tweedie, is built on the framework of the |
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existing ext2 filesystem; in fact, ext3 is very similar to ext2 except for one |
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small (but important) difference -- it supports journaling. Yet even with this |
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small addition, I think you'll find that that ext3 has several surprising and |
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intriguing capabilities. In this article, I'll give you a good understanding |
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of how ext3 compares to the other journaling filesystems currently available. |
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In my next article, we'll get ext3 up and running. |
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</p> |
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|
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</body> |
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</section> |
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</chapter> |
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|
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<chapter> |
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<title>Understanding Ext3</title> |
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<section> |
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<body> |
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|
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<p> |
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So, how does ext3 compare to ReiserFS? In previous articles, I explained how |
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ReiserFS is well suited to handling small files (under 4K), and in certain |
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situations, ReiserFS' small file performance is ten to fifteen times greater |
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than that of ext2 and ext3. However, while ReiserFS has many strengths, it also |
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has weaknesses. In the current implementation of ReiserFS (version 3.6), |
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certain file access patterns can actually result in significantly worse |
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performance than ext2 and ext3, particularly when reading large mail |
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directories. Also, ReiserFS doesn't have a good track record of NFS |
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compatibility and has poor sparse file performance. In contrast, ext3 is a very |
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well-rounded filesystem. It's a lot like ext2; it's not going to give you the |
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blazingly fast small-file performance that ReiserFS gives you, but it's not |
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going to give you any unexpected performance or functionality hiccups either. |
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</p> |
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|
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<p> |
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One of the nice things about ext3 is that because it is based on the ext2 code, |
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ext2 and ext3's on-disk format is identical; this means that a cleanly |
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unmounted ext3 filesystem can be remounted as an ext2 filesystem with |
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absolutely no problems. And that's not all. Thanks to the fact that ext2 and |
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ext3 use identical metadata, it's possible to perform in-place ext2 to ext3 |
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filesystem upgrades. Yes, you read that right. By upgrading a few key system |
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utilities, installing a modern 2.4 kernel and typing in a single tune2fs |
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command per filesystem, you can convert your existing ext2 servers into |
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journaling ext3 systems. You can even do this while your ext2 filesystems are |
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mounted. The transition is safe, reversible, and incredibly easy, and unlike a |
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conversion to XFS, JFS, or ReiserFS, you don't need to back up and recreate |
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your filesystems from scratch. Now, for a moment, consider the thousands of |
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production ext2 servers in existence that are just minutes away from an ext3 |
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upgrade; then, you'll have a good grasp of ext3's importance to the Linux |
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community. |
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</p> |
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|
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<p> |
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If I had to describe ext3 in one word, I'd call it "comfortable". It's |
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incredibly easy to ext3-enable an existing ext2 system, and after you do, |
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you're not going to run into any unexpected performance quirks. And there's yet |
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another way that ext3 excels in the comfort department; ext3 happens to be one |
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of the most reliable journaled filesystems available for Linux, as I explain |
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below. |
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</p> |
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|
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</body> |
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</section> |
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</chapter> |
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|
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<chapter> |
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<title>Ext3 reliability</title> |
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|
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<section> |
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<body> |
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|
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<p> |
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In addition to being ext2-compatible, ext3 inherits other benefits by sharing |
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ext2's metadata format. For one, ext3 users gain access to a rock-solid fsck |
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tool. You'll recall that one of the points of using a journaling filesystem is |
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to avoid the need for an exhaustive fsck in the first place; however if you do |
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end up getting corrupt metadata, either from a flaky kernel, bad hard drive, or |
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something else, you'll greatly appreciate the fact that ext3 inherits ext2's |
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fsck. In contrast, ReiserFS' fsck is in its infancy, and fixing flaky metadata |
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when it does show up can be a difficult and dangerous process. |
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</p> |
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|
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</body> |
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</section> |
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|
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<section> |
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<title>Metadata-only journaling</title> |
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<body> |
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|
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<p> |
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Interestingly, ext3 handles journaling very differently than ReiserFS and other |
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journaling filesystems do. With ReiserFS, XFS, and JFS, the filesystem driver |
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journals metadata, but makes no provisions for journaling data. With |
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metadata-only journaling, your filesystem metadata is going to be rock solid, |
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and you will probably never need to perform an exhaustive fsck. However, |
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unexpected reboots and system lock-ups can result in significant corruption of |
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recently-modified data. Ext3 uses a couple of innovative solutions to avoid |
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these problems, which we'll look at in a bit. |
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</p> |
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|
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<p> |
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But first, it's important to understand exactly how metadata-only journaling |
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could end up biting you. As an example, let's say that you were modifying a |
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file called /tmp/myfile.txt when the machine unexpectedly locked up, forcing a |
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reboot. If you were using a metadata-only journaling filesystem such as |
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ReiserFS, XFS or JFS, your filesystem metadata would be easily repaired, thanks |
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to the metadata journal, and you wouldn't need to sit through a laborious fsck. |
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</p> |
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|
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<p> |
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However, there's the distinct possibility that when you load /tmp/myfile.txt |
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into a text editor, your file will not simply be missing recent changes, but |
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will contain a good amount of garbage and may even be completely unreadable. |
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This isn't something that will always happen, but it could happen and often |
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does. |
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</p> |
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|
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<p> |
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Here's why. Typical journaled filesystems like ReiserFS, XFS, and JFS take |
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extra special care of metadata, but don't pay too much attention to data. In |
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our above example, the filesystem driver was in the process of modifying |
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several filesystem blocks. The filesystem driver updated the appropriate |
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metadata, but didn't have time to flush the data from its caches to the new |
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blocks on disk. Thus, when you loaded up /tmp/myfile.txt into a text editor, |
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part or all of the file contained garbage -- blocks of data that didn't get |
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initialized in time before the system locked up. |
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</p> |
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|
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</body> |
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</section> |
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|
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</chapter> |
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|
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<chapter> |
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<title>The ext3 approach</title> |
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<section> |
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<body> |
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|
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<p> |
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Now that we have a good general understanding of this problem, let's look how |
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ext3 implements journaling. In ext3, the journaling code uses a special API |
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called the Journaling Block Device layer, or JBD. The JBD has been designed for |
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the express purpose of implementing a journal on any kind of block device. |
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Ext3 implements its journaling by "hooking in" to the JBD API. For example, the |
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ext3 filesystem code will inform the JBD of modifications it is performing, and |
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will also request permission from the JBD before modifying certain data on |
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disk. By doing so, the JBD is given the appropriate opportunities to manage the |
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journal on behalf of the ext3 filesystem driver. It's quite a nice |
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arrangement, and because the JBD is being developed as a separate, generic |
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entity, it could be used to add journaling capabilities to other filesystems in |
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the future. |
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</p> |
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|
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|
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|
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1.1 xml/htdocs/doc/en/articles/prompt-magic.xml |
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|
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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/prompt-magic.xml?rev=1.1&content-type=text/x-cvsweb-markup&cvsroot=gentoo |
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plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/prompt-magic.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo |
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|
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Index: prompt-magic.xml |
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=================================================================== |
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<?xml version="1.0" encoding="UTF-8"?> |
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> |
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/articles/prompt-magic.xml,v 1.1 2005/08/21 22:23:44 neysx Exp $ --> |
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|
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<guide link="/doc/en/articles/prompt-magic.xml" lang="en"> |
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|
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<title>Prompt magic</title> |
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|
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<author title="Author"> |
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<mail link="drobbins@g.o">Daniel Robbins</mail> |
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</author> |
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<author title="Editor"> |
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<mail link="jackdark@×××××.com">Joshua Saddler</mail> |
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</author> |
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|
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<abstract> |
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Why stick with the standard boring shell prompt when you can easily make it |
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colorful and more informative? In this tip, Daniel Robbins will show you how to |
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get your shell prompt just the way you like it, as well as how to dynamically |
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update your X terminal's title bar. |
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</abstract> |
| 246 |
|
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<!-- The original version of this article was first published on IBM |
| 248 |
developerWorks, and is property of Westtech Information Services. This |
| 249 |
document is an updated version of the original article, and contains |
| 250 |
various improvements made by the Gentoo Linux Documentation team --> |
| 251 |
|
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<version>1.0</version> |
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<date>2005-08-21</date> |
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|
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<chapter> |
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<title>Enhancing the system prompt</title> |
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<section> |
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<body> |
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|
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<note> |
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The original version of this article was first published on IBM developerWorks, |
| 262 |
and is property of Westtech Information Services. This document is an updated |
| 263 |
version of the original article, and contains various improvements made by the |
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Gentoo Linux Documentation team. |
| 265 |
</note> |
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|
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<p> |
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As Linux/UNIX people, we spend a lot of time working in the shell, and in many |
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cases, this is what we have staring back at us: |
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</p> |
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|
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<pre caption="The normal user prompt"> |
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bash-2.04$ |
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</pre> |
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|
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<p> |
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If you happen to be root, you're entitled to the "prestige" version of this |
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beautiful prompt: |
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</p> |
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|
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<pre caption="The root prompt"> |
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bash-2.04# |
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</pre> |
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|
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<p> |
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These prompts are not exactly pretty. It's no wonder that several Linux |
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distributions have upgraded their default prompts that add color and additional |
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information to boot. However, even if you happen to have a modern distribution |
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that comes with a nice, colorful prompt, it may not be perfect. Maybe you'd |
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like to add or change some colors, or add (or remove) information from the |
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prompt itself. It isn't hard to design your own colorized, tricked-out prompt |
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from scratch. |
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</p> |
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|
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</body> |
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</section> |
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<section> |
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<title>Prompt basics</title> |
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<body> |
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|
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<p> |
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Under bash, you can set your prompt by changing the value of the <c>PS1</c> |
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environment variable, as follows: |
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</p> |
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|
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<pre caption="Altering the environment variable"> |
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$ <i>export PS1="> "</i> |
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> |
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</pre> |
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|
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<p> |
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Changes take effect immediately, and can be made permanent by placing the |
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<c>export</c> definition in your <path>~/.bashrc</path> file. <c>PS1</c> can |
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contain any amount of plain text that you'd like: |
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</p> |
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|
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<pre caption="A custom prompt"> |
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$ <i>export PS1="This is my super prompt > "</i> |
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This is my super prompt > |
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</pre> |
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|
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<p> |
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While this is, um, interesting, it's not exactly useful to have a prompt that |
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contains lots of static text. Most custom prompts contain information like the |
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current username, working directory, or hostname. These tidbits of information |
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can help you to navigate in your shell universe. For example, the following |
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prompt will display your username and hostname: |
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</p> |
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|
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<pre caption="A more useful prompt"> |
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$ <i>export PS1="\u@\H > "</i> |
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drobbins@freebox > |
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</pre> |
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|
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<p> |
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This prompt is especially handy for people who log in to various machines under |
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various differently-named accounts, since it acts as a reminder of what machine |
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you're actually on and what privileges you currently have. |
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</p> |
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|
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<p> |
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In the above example, we told bash to insert the username and hostname into the |
| 343 |
prompt by using special backslash-escaped character sequences that bash |
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replaces with specific values when they appear in the <c>PS1</c> variable. We |
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used the sequences <c>\u</c> (for username) and <c>\H</c> (for the first part |
| 346 |
of the hostname). Here's a complete list of all special sequences that bash |
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recognizes (you can find this list in the bash man page, in the "PROMPTING" |
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section): |
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</p> |
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|
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<table> |
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<tr> |
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<th>Sequence</th> |
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<th>Description</th> |
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</tr> |
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<tr> |
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<ti>\a</ti> |
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<ti>The ASCII bell character (you can also type <c>\007</c>)</ti> |
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</tr> |
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<tr> |
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<ti>\d</ti> |
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<ti>Date in "Wed Sep 06" format</ti> |
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</tr> |
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<tr> |
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<ti>\e</ti> |
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<ti>ASCII escape character (you can also type <c>\033</c>)</ti> |
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</tr> |
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<tr> |
| 369 |
<ti>\h</ti> |
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<ti>First part of hostname (such as "mybox")</ti> |
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</tr> |
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<tr> |
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<ti>\H</ti> |
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<ti>Full hostname (such as "mybox.mydomain.com")</ti> |
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</tr> |
| 376 |
<tr> |
| 377 |
<ti>\j</ti> |
| 378 |
<ti> |
| 379 |
The number of processes you've suspended in this shell by hitting <c>^Z</c> |
| 380 |
</ti> |
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</tr> |
| 382 |
<tr> |
| 383 |
<ti>\l</ti> |
| 384 |
<ti>The name of the shell's terminal device (such as "ttyp4")</ti> |
| 385 |
</tr> |
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<tr> |
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<ti>\n</ti> |
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<ti>Newline</ti> |
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</tr> |
| 390 |
<tr> |
| 391 |
<ti>\r</ti> |
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<ti>Carriage return</ti> |
| 393 |
</tr> |
| 394 |
<tr> |
| 395 |
<ti>\s</ti> |
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<ti>The name of the shell executable (such as "bash")</ti> |
| 397 |
</tr> |
| 398 |
<tr> |
| 399 |
<ti>\t</ti> |
| 400 |
<ti>Time in 24-hour format (such as "23:01:01")</ti> |
| 401 |
</tr> |
| 402 |
<tr> |
| 403 |
<ti>\T</ti> |
| 404 |
<ti>Time in 12-hour format (such as "11:01:01")</ti> |
| 405 |
</tr> |
| 406 |
<tr> |
| 407 |
<ti>\@</ti> |
| 408 |
<ti>Time in 12-hour format with am/pm</ti> |
| 409 |
</tr> |
| 410 |
<tr> |
| 411 |
<ti>\u</ti> |
| 412 |
<ti>Your username</ti> |
| 413 |
</tr> |
| 414 |
<tr> |
| 415 |
<ti>\v</ti> |
| 416 |
<ti>Version of bash (such as 2.04)</ti> |
| 417 |
</tr> |
| 418 |
<tr> |
| 419 |
<ti>\V</ti> |
| 420 |
<ti>Bash version, including patchlevel</ti> |
| 421 |
</tr> |
| 422 |
<tr> |
| 423 |
<ti>\w</ti> |
| 424 |
|
| 425 |
|
| 426 |
|
| 427 |
-- |
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