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Thursday, May 16, 2002TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
A Case For Certification
SUN Introduces New Cobalt Server
SUN and Linux, A Publicity Stunt?
SSH Replaces R\* in OpenBSD3) Linux Resources
Linux Terminal Servers
^?^?^?^?What's Going On?
Free Training Materials
Dual Boot Linux and... Linux?
SSL Made Easy4) App o’ the Week
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1) Sean’s Notes
Last week we had a look at filesystems, and what they do for us. If you’re new to this newsletter, or want a refresher, take a look here:
http://ertw.com/~sean/newsletter/May+9%2C+2002
I left off just before telling you how to mount a filesystem with the “mount” command. It’s really quite easy, as long as you’re root:
mount what_you_want_to_mount where_you_want_to_mount_it
So if you want to mount /dev/hdb5 on /mnt (so that when you’re in /mnt, you’re reading and writing to hdb5)
mount /dev/hdb5 /mnt
Then, you can check to see that it’s mounted:
mount
… /dev/hdb5 on /mnt type ext2 (rw)
Note that we didn’t mention anything about what type of filesystem was on hdb5, it was figured out for us. Sometimes, you have to tell mount the filesystem type:
mount /dev/hdb5 /mnt -t ext2
-t tells the filesystem type. You can look at /proc/filesystems to see what is currently available, or see what drivers you could load in /lib/modules/kernel_version/kernel/fs
/etc/fstab is the file that controls what gets mounted on boot. To have hdb5 mounted every boot, we could add the line
/dev/hdb5 /mnt ext2 defaults 1 2
(fields are separated by spaces or tabs) The data should look familiar, columns 1-3 are the device (what you want to mount), the mount point (where you want to mount it), and the filesystem type respectively. The next field is where you can pass options, normally we use “default” to specify that we don’t really care. Examples of options would be “ro” to make it mounted read only. The second from last field isn’t really used anymore, it’s used for backups but rarely referenced in real life. The last field is for fsck (the file system checker) so that it knows which order to check things in. Other than the root filesystem, you should leave it at 2.
The first field need not be in the form /dev/hdXN. If the filesystem type were NFS (network file share), it would be
machine:/share/name
With the smbfs filesystem, you can use UNC style shares
//machine/share
though you’ll need to pass options such as username and password in the fourth field (run /sbin/mount.smbfs to find what they are).
Does the device have to be a device or machine? How about another file? Got an iso image of a CD-ROM handy? (you can make one via dd if=/dev/cdrom of=image.iso)
mount image.iso /mnt -t iso9660 -o loop
cd /mnt; ls
What you did there was mount an image of a CD as if it were a CD itself. It’s a handy trick!
Another benefit of using fstab is that you can specify only the mount point or device when using mount. With the line above in /etc/fstab, we can run
mount /mnt
or
mount /dev/hdb5
without having to specify the filesystem type or other options.
Now that mounting filesystems is out of the way, we should take a look at some of the filesystems out there.
ext2 is the stock filesystem in use today. It offers regular UNIX permissions (group/owner/everybody read/write/execute), support for file attributes (immutable, synchronous updates, append only), and fairly good performance. When you get a directory with lots of files, though, performance suffers because of the way data is laid out. I’ll be getting into some of the internals in a future article. Another downside to ext2 is that if the filesystem is unmounted uncleanly (i.e. power outage), corruption may occur.
ext3 is ext2 with journaling. Journaling means that when a write is done to disk, it is written to a log immediately. If something happens, the system can replay the log and be at a good state very quickly. Those that have had to sit through a file system check on a 20+ gig ext2 partition will appreciate this. ext3 is also backward compatible with ext2 – you can mount the volume as ext2 with an old kernel. You can also convert an ext2 filesystem to ext3 very easily, all you end up doing is adding a journal.
ReiserFS (http://www.namesys.com/) is another journaling filesystem that was designed to overcome some of ext2’s inefficiencies. It treats the filesystem as a database, allows very fast file lookups, and conserves space. Remember the concept of a cluster from FAT? If your cluster size is 8K, and your file is 8K+1byte, you take up two clusters, wasting 8K-1 bytes. With lots of files,that can add up! ReiserFS allows files to share the clusters to conserve space. ReiserFS shines on a filesystem with many small files, such as a mail spool or web cache. It’s also a newer development, so things are constantly changing.
I’d be remiss if I didn’t mention IBM’s JFS (http://oss.software.ibm.com/developerworks/opensource/jfs/) and SGI’s XFS (http://oss.sgi.com/projects/xfs/). They’re both Open Source versions of tried and proved filesystems, and I applaud the vendor’s willingness to help the ports to proceed. Not being familiar with them, I invite anyone who has used them to let me know what they found out.
The choice of filesystem depends on the properties of the data, and your acceptance of complexity. I can think of few good reasons that one would choose ext2 when ext3 is around, but choosing between ext3, ReiserFS, JFS, and XFS is difficult. Even if one only looked at the more familiar ext3 and ReiserFS, the data still makes all the difference. Here’s where a test machine comes in handy: which one offers better performance? Which are you going to feel comfortable recovering at 3am?
I should mention on that last note that the latest stable kernel, 2.4.18, includes ext2, ext3, and ReiserFS. 2.5.15, the latest unstable version, adds in JFS. According to SGI’s site, XFS patches are being submitted for inclusion into 2.5, but work has to be done on cleaning up the code.
Well, my faithful readers, that’s filesystems in a nutshell. In the past two weeks we’ve looked at what a filesystem is, how you use them, and what kinds are available. I’ve already had a couple of requests to get into the internals of ext2, including answering that age old question “Why are there no defraggers for Linux?” I’ll try not to disappoint. I always appreciate hearing your comments on past and future articles, or on Linux in general.
A small note before I sign off: The May issue of Linux Magazine is a must read for anyone who is looking to integrate Linux into their network management. There are outstanding articles on IPv6, statistics collection, and availability monitoring.
Long live the Penguin, Sean mailto:swalberg@cramsession.com
2) Linux News
A Case For Certification
Recent convert QCumber decided he’d have a little fun. He applied for 10 job ads looking for a Microsoft administrator. First he applied with a resume making no mention of Linux. Then, he applied under a different name with the same resume that included Linux certs. Do you think it made a difference? You might be surprised!
http://boards.cramsession.com/boards/vbm.asp?mU6846
SUN Introduces New Cobalt Server
“Sun Microsystems announces a higher-end addition to its Cobalt line of Linux-powered servers today: up to a 1.26 GHz Pentium processor, two 80-gig hard drives and 2 gigs of SDRAM aimed at small-to-medium enterprises. The RaQ 550, with an updated easily configurable Web-based GUI similar to the ones offered on other Cobalt models, will be available June 10 with a price tag of $1,699 to $2,899, depending on the configuration of the machine. The goal of the Web interface is ‘extreme ease of use.’”
http://newsforge.com/newsforge/02/05/13/015205.shtml?tid=7
SUN and Linux, A Publicity Stunt?
SUN has made several statements indicating that they’d like to converge Solaris and Linux to make it easier for developers to target both platforms. Is this really their goal, or is it a publicity stunt?
http://news.com.com/2100-1001-912666.html
SSH Replaces R* in OpenBSD
It’s been the default for quite some time, but OpenBSD is stopping distribution of the rlogin and rexec daemons. OpenBSD leads the pack in terms of security, so I’m hoping that the Linux crowd follows suit.
http://www.deadly.org/article.php3?sid 020514010017
3) Linux Resources
Linux Terminal Servers
While the thin client concept is nothing new for Unix, the Linux Terminal Server Project makes it very easy to deploy old PCs as thin clients. Take a peek at the documentation to see what LTSP can do for you, I was surprised at how automated everything was!
http://www.ltsp.org/documentation/ltsp-3.0.0/ltsp-3.0.html
^?^?^?^?What’s Going On?
Ever fired up vi, but whenever you hit backspace you see “^?”? Rather than use the delete key, there is a way to fix this behavior.
http://www.redhat.com/mailing-lists/guinness-list/msg11505.html
Free Training Materials
Here are some training guides for the LPIC level I courses. While they’re made for trainers, they should still be of use to the self-study crowd.
http://www.linuxtraining.co.uk/download/
Dual Boot Linux and… Linux?
It’s quite a common question… “How do I dual-boot Windows and Linux?” What about dual-booting Linux with another installation of Linux? Try out a couple of your favourite distros, or maybe keep an older one around for safety purposes!
http://www-106.ibm.com/developerworks/linux/library/l-dboot.html
SSL Made Easy
Apache 2.0 is a great step forward for the Apache web server. Here’s a great document on how to configure SSL security in many different ways. I’m pleased with the style of this document, I wish others would follow this format.
http://httpd.apache.org/docs-2.0/ssl/ssl_howto.html
4) App o’ the week
Nothing like a bit of mindless violence to pass the time. Falsoyd is “Falsoyd’s A Little Shoot-em-up On Your Desktop” Quite rudimentary at the moment, but it’s a quick way to take out some frustrations after dealing with an annoying user… Yea, you know the one.
http://sourceforge.net/projects/falsoyd
(C) 2002 BrainBuzz.com, Inc. All Rights Reserved.
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