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Diagnosing random crashes

Post date: April 13, 2005, 05:04 Category: Miscellaneous Views: 4033 Comments
Tutorial quote: Solaris will exercise everything on a PC. I have seen machines run just fine with Windows for months and crash during a Solaris x86 install. The reason was always marginal parts/specs/timings/temperatures that were never pushed to the failure limits until Solaris x86 was installed.

Software RAID and Encrypted Filesystem Benchmarks

Post date: January 25, 2006, 23:01 Category: Benchmarks Views: 4714 Comments
Tutorial quote: Both tests use bonnie++ to test the disks.

- Files Test: create, destroy, and stat 20,000 files in sequential and random order. File sizes are random between 0K and 15k. All files are created in a single directory.
- IO Test: read, write, rewrite, and seek in three 1GB size files.
- Load: all tests are starting with 0 cpu load. Load was then measured every 2 seconds for the duration of the test and averaged over all measurements.

Talking clock, written in bash using common utilities

Post date: October 20, 2006, 19:10 Category: Programming Views: 3869 Comments
Tutorial quote: Build your own talking clock, using Bash and some common *nix utilities like sox. Articluates the time at random once an hour and hour and with a random pitch.
Includes very basic short scripts to get you going on basic bash coding and then puts it all together to produce the finished item.
Takes time out to explain as much as possible to a large audience.

Getting started with RHEL4's built-in LVM tools

Post date: June 3, 2005, 16:06 Category: System Views: 6035 Comments
Tutorial quote: Many Unix administrators I know (you know who you are), always used to smirk when I talked about Linux. They could always point to the fact that regardless of whatever I could say, they had journaling file systems, which they could manage using various Logical Volume Management (LVM) tools, and I couldn't touch that.

Well, not any more! Not only does Red Hat offer ext3 as their default file system, but they offer great management tools to boot. As we know, ext2 had a great lifespan, but it was not an enterprise-ready file system that could handle large disk partitions, fast recovery from systems crashes, or large amounts of files. Journaling file systems give you the ability to recover almost instantly from a crash, as you do not need to run fsck after a restart. Similar to how databases recover from crashes, a journaling file system tracks changes to file system metadata and pretty much guarantees that either all or no updates have completed. Of course, these file systems also need elaborate tools to help better configure and manage them accordingly.

Easy peasy full system backup

Post date: August 12, 2008, 12:08 Category: Miscellaneous Views: 3162 Comments
Tutorial quote: You know how when someone accidentally deletes their files or their hard drive crashes or some other apocalyptic event occurs, the first thing people ask is “where is your backup”? Of course, we’ve all seen it (*ahem* been there ). It’s a bit unintuitive, because backups have no equivalent in the real world. If you drive your car into a lake, there’s no way to get it back. But making backups is the single best way to prevent losing your stuff. So do it!

Downloading without a Browser

Post date: November 29, 2005, 19:11 Category: Software Views: 2920 Comments
Tutorial quote: Ever had to download a file so huge over a link so slow that you'd need to keep the web browser open for hours or days? What if you had 40 files linked from a single web page, all of which you needed -- will you tediously click on each one? What if the browser crashes before it can finish? GNU/Linux comes equipped with a handy set of tools for downloading in the background, independent of the browser. This allows you to log out, resume interrupted downloads, and even schedule them to occur during off-peak Net usage hours.

Connecting to a Wireless LAN with Linux, Part 2

Post date: April 13, 2005, 19:04 Category: Hardware Views: 3637 Comments
Tutorial quote: In Part 1 we reviewed hardware options, which wireless utilities should be present, how to use Windows drivers, and how to be open to connect to any available wireless access point. Today we'll cover configurations on Red Hat- and Debian-type systems, basic security, and hardware discovery.

Wireless connectivity can be rather overly friendly, allowing connections from anyone. This howto assumes you have a wireless access point on a LAN, which can be all wireless or mixed wired and wireless. You don't want it wide open to just any random person with a desire to snoop on your network or "borrow" your bandwidth, but you want some access controls and security. Your access point should have a unique SSID (service set identifier), WEP (wireless equivalent privacy) or WPA/WPA2 (Wi-fi protected access) set up and working, and either a DHCP server or a pool of assigned IP addresses for clients.

Creating Snapshot-Backups with FlyBack On Ubuntu 7.10

Post date: February 3, 2008, 13:02 Category: Desktop Views: 3311 Comments
Tutorial quote: FlyBack is a tool similar to Apple's TimeMachine. It is intended to create snapshot-backups of selected directories or even your full hard drive. From the FlyBack project page: "FlyBack is a snapshot-based backup tool based on rsync. It creates successive backup directories mirroring the files you wish to backup, but hard-links unchanged files to the previous backup. This prevents wasting disk space while providing you with full access to all your files without any sort of recovery program. If your machine crashes, just move your external drive to your new machine and copy the latest backup using whatever file browser you normally use." This article shows how to install and use FlyBack on Ubuntu 7.10 (Gutsy Gibbon).

Creating a safe directory with PAM and Encfs

Post date: June 7, 2006, 20:06 Category: Security Views: 3134 Comments
Tutorial quote: Now, in my network (and others) the credentials provided at login could (and should) be used by those programs. How can you retrieve these credentials, providing enough security?
With a the PAM modules pam_script it's possible to store the password in a file, which will be used by fusemb and mount.cifs to read the password from.

To achieve security, one could make the user logging in owner and deny read/write for anybody else. Remove this file when the user ends his/her session.
This is enough, for runtime. But I was wondering, but what if the system crashes, and the file with the credentials remains on the harddrive? Anybody who is able to mount this harddrive with for example a lifecd, can read this file!

That's why I was looking for a way to encrypt this file.

With encfs this is very possible! At run time it gives an interface to encrypted files and directories, which does only exist at runtime! When the system is not running, there are only encrypted files, useless when you do not know the key to it. And this key is exactly the (encrypted) password! That's why I've chosen for a combination of PAM and Encfs.

Tunneling the hard way: using slirp, pppd and socat

Post date: January 29, 2006, 13:01 Category: Network Views: 11227 Comments
Tutorial quote: Every now and then you might come across a "bad" ISP. The one I have at home for example is dropping UDP packets ever so often when I try to play online games -- and it tends to drop random packets while I try to log onto a gameserver too which makes a certain game I like to play crash during the loading phase so it can't recover. I also heard of other ISPs blocking certain ports on external servers -- universities for example seem to like blocking p2p network ports and the school i was attending till last august blocked everything but port 80 for http -- including ftp which made even on-topic "research" a pita at times.
Usually there's three ways of working around this problem if "giving up" is not an option to you: a) change your ISP, b) use ssh to redirect ports, c) connect to an external VPN to route for you. a) can be tricky -- it's impossible if you're sharing the link with your parents and they insist on their email addresses or in the university/workplace/school scenario. b) will only work with single port/host combinations and for c) you will need a full-fledged rootbox idling around on the internet -- which tend to be expensive and "virtual servers" might not work because those often don't include tun/tap devices and/or kernel-level ppp support if you rent them and in case you rented them you probably can't fiddle around with its kernel to enable it (that was my problem at least). If any of this rings a bell to you, read on and discover method d)
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