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snapshot: Tech Words of the Day

snapshot: A filesystem technique that allows leisurely backups while continuing to use the system. This magic is accomplished by making a special copy of a directory or filesystem (the exact mechanics will vary with the product you are using) that doesn't really copy anything unless and until data changes at the source. Here's how it works: Let's say that you have created a snapshot of some directory in /snap. If you read files in /snap, they look just like the files they were created from. Actually, you are still reading from the original data blocks at this point.

Title Last Comment
fgconsole: Tech Words the Day  
- This Linux command returns the number of the console you are using: if you were on ALT-F1, it would return 1, ALT-F2 would be 2, etc. It's hard to imagine where this would be useful except perhaps in some script that you don't want to run on certain consoles for some reason. -

reptile: Tech Words the Day  
- http://reptile.openprivacy.org/. Maybe I just don't get this. Reptile distributes RSS feeds: OK. Wouldn't a supernode be the same as any RSS integrator like Syndic8? -

T-1, T-3, OC-3: Tech Words the Day  
- A T-1 line is 24 telephone channels of 64Kb each. A T-3 is 672 channels or 28 T1's. You'll also see a T-1 referred to as DS1, and T-3's as DS3. A T-1 is about 1.54 Mbps, a T-3 about 43 Mbps. Above that, we get into OC (Optical Carrier) territory. -

rebol: Tech Words the Day  
- Another odd little scripting language. I was particularly amused at the so called "FAQ". -

SELinux: Tech Words the Day  
- SELinux is a Mandatory Access Control system. You can get an idea of how you'd configure this at my Selinux on FC5 article even though it's a few years old, but before you read that, just let me put on my flame proof suit here... ok, I'm ready: I almost always disable SELinux sooner or later. -

ARIN, APNIC, LAPNIC, RIPE: Tech Words the Day  
- Internet registries. ARIN hands out addresses for North America, a portion of the Caribbean and sub-Saharan Afric (strange, isn't it?); RIPE handles Europe, the Middle East and parts of Africa and Asia; LACNIC is Latin America and the rest of the Caribbean; -

quine: Tech Words the Day  
- A self-reproducing program; that is, a program that creates a copy of itself. These have ben written in just about any language you can think of, and you can find multiple examples at http://www.nyx.net/~gthompso/quine.htm -

snert: Tech Words the Day  
- Take your pick: Snot Nosed, Eros-Ridden Teenager Snot Nosed Egocentric Retentive Turd Snot Nosed Egotistical Raging Teen and others. Whatever the true derivation, it's not a friendly appellation. -

Kleene star: Tech Words the Day  
- The '*' used in regular expressions. Stephen Kleene (pronounced Klay-knee, by the way) invented regular expressions. -

acl: Tech Words the Day  
- Access Control List. Basically, extended permissions. Some modern Unixes (Linux, UW, and others) have extended the permissions model. This requires new commands beyond chmod, and may be limited to certain types of filesystems. -

WiMax: Tech Words the Day  
- Other countries already have 100 Mbit connnections in common use. The USA could do that too, but political wrangling over broadcast spectrum has prevented it. -

RFC: Tech Words the Day  
- Request For Comments are the tech notes for the Internet. Anyone can submit an RFC, though it must be approved first by the RFC Editor (which for many years was a single person named Jon Postel -

mtu: Tech Words the Day  
- Maximum Transmission Unit. Every time you send mail, or transfer a file on your local network, or indeed do anything at all that involves communicating with another machine, data is broken up into packets of a specific size. -

Avatar: Tech Words the Day  
- A semi-commercial replacement for cron. It's free for personal use: 'Vexus is dedicated to providing something back to the community so personal copies of Avatar are free.' Cron certainly does have limitations. -

bochs: Tech Words the Day  
- You have a BIOS, the cpu is emulated, the disk is emulated, everything -

- Computers screw up. You can have meaningless instructions, attempts to divide by zero, attempts to access non-existent memory, and more. -

- Print filters. Whether it's CUPS, LPRng or plain old LPD, you often need a filter in between application data and the physical printer. In olden times, you'd use specific filters for specific purposes, but the trend now is to Swiss army knife, do everything programs. -

- The FBI's ip wiretapping software, since renamed 'DCS1000'. After a court order allowing it, the FBI would install a computer at your ISP's premises to monitor your packets. -

- Embeddable Linux. The intent here is to port Linux to 8086 and 80286 processors. Why not? Xenix ran on those, and while the lack of a protected mode CPU on the 8086, and the limited powers of the 80286 make it all make it all challenging, I had Xenix installations doing real work on 8086 machines. -

Hurd   2011/07/05 TonyLawrence
- The meaning of Hurd is self-referentially recursive. It intends to be the GNU OS. It seems that it is always 'close to ready', and perhaps that is where it always will be. -

- A tool for cracking Wireless networks: http://airsnort.shmoo.com/. Yes, it's possible to crack the encryption of WEP wireless networks. However, it requires examining a LOT of packets - this could be months worth of monitoring. -

- WTAIL is 'tail' for windows. Except it isn't really. Unix tail is much more flexible, and GNU tail is even more so. -

- Mach is a microkernel system, which means that most of the features that are ordinarily within the kernel are instead separate servers - think of them as daemons, though they aren't necessarily running in user space. -

sack: Tech Words the Day  
- Selective Acknowledgements RFC-2018 are turned off or on in Linux by setting net.ipv4.tcp_sack (in /etc/sysctl.conf ) to 0 or 1. The purpose of this feature is to cut down on retransmisson of packets on bad networks. -

MTTR: Tech Words the Day  
- What this is actually referring to is whether or not your CPU has Memory Type Range Registers -

WebDAV: Tech Words the Day  
- The web page makes it sound like it's just another FrontPage or whatever, but it is much more than that. -

fresnel zone: Tech Words the Day  
- You'll hear this in the context of radio transmission, for example when you need to network two buildings by a radio link. The farther apart the antennas, the bigger the Fresnel zone gets - it's the area clear of obstructions that you need for a clean signal. -

tuple: Tech Words the Day  
- An n-tuple would be a list like that of indeterminate length. That tuple uses commas to separate its members, but the separator isn't what makes it a tuple. -

setpci: Tech Words the Day  
- Linux users can list their PCI devices with lspci (SCO users can use 'hw -r pci' for a similar listing). 'setpci' is a little known companion that you may never need, but will be happy to know about if you ever do. -

spoofing: Tech Words the Day  
- IP spoofing is the technique of sending packets that are apparently from some other machine. The usual reason for this is that it is part of a Denial of Service attack. -

FSF: Tech Words the Day  
- The Free Software Foundation was founded in 1985, long before most of the world owned personal computers. Richard Stallman (RMS) actually laid the seeds for this in 1983 when he announcd the GNU project. -

- If the code you downloaded has a "configure" script, "autoconf" probably created it. -

- Simultaneous Peripheral Operation On-Line. Though it probably originated in the thought that you have a 'spool' of magnetic tape. Nowadays we don't use the term much except in the context of printing: we 'spool' a print job to disk and it goes to the printer -

- Sun's (Solaris) Dynamic Tracing Tool. If you just look at this quickly, you'll think 'Oh, like lsof'. Well, yeah, 'like' lsof, but much more. -

- Idleout inactive users. Commonly this is for security and for getting people the heck off before backups. It's actually a much more complicated task than you might think: truly determing inactivity is pretty tricky. -

- In earlier days of the internet, you'd sometimes see a signature that looked like this: -----BEGIN GEEK CODE BLOCK----- Version: 3.1 GIT' followed by more gibberish. Not very many people do this anymore. -

- NoteEdit for Linux. I don't grok music. Never have understood it, in spite of being fascinated by it from an early age. I've tried to learn to play piano more than once, and failed miserably every time. -

- Did sixth grade teach you anything? Style and diction analyze your writing, and style includes an estimate of a matching grade level in its output. While that is often used to poke fun at the semi-literate, careful authors sometimes use it the other way: -

- Bastille is a security hardening script - it asks questions like 'Would you like to disable SUID status for at?' and you answer. -

- Another programming language: The Haskell Programming Language. As with every other programming language, the proponents explain that other programming languages are difficult and hard to use, but but this one, yes, this one is different! And of course it really isn't. -

- Microsoft's open source Windows Installer XML project. Huh? Microsoft embracing open source? Well, do note that this is something that creates Microsoft setup packages, so there's little altruism here. -

- Remote Procedure Call. The concept here is that a program on one computer can use a service on another computer without being bothered with the details of network communication. The 'rpcinfo' program can tell you what rpc services are available on a server; -

- This is an interface that leaves open views open. If applied to a web browser, it would mean that every link you clicked on would get a new window. Most folks wouldn't like that, but the designers of some file system interfaces, notable Gnome, insist that is how file system navigation should work. -

- Plain Old Telephone Service. This acronym has been in use for quite a while, almost before there really was much else other than plain old telephone service. POTS is circuit based, and of course the newer concept is packets. -

- A set of recompiled programs that hide the activities of someone who has hacked and taken over your system. The programs would include such things s 'ps', 'netstat', 'who', etc. on Unix systems and their analogs on Windows. -

- A Bogon address is an ip address that shouldn't be in a routing table and therefore shouldn't be used for hosts or devices. These are not the just the reserved private addresses we use for internal networks. Bogon addresses are often used as the source addresses of DDoS packets. -

- Concurrent Versions Systems. The general standard for version control. Allows multiple people to work on a project by tracking changes and controlling access. Primarily used for code, but there's no reason it can't be used for any project where multiple people modify files. -

- The grand-daddy of spreadsheets, and still available today in its original glory: VisiCalc Executable for the IBM PC. Another early spreadsheet was Multiplan, which realy was quite advanced for its day, offering linked sheets and other powerful features. -

- A restricted shell for specific use with scp and sftp. It is configurable, o you can add or subtract apps it can use, but the base purpose is to provide security for file transfers. Often used in conjunction with chroot for even greater lockdown. -

- A powerful scripting language very popular in the Unix world, probably because anyone familiar with Unix tools like awk and sed can quickly make use of Perl's much more powerful abilities. -


- Although separate programs, you'll often see the two tied together. From the Bugs section of the Lex Man Page: 'The asteroid to kill this dinosaur is still in orbit.' Lex is 'A Lexical Analyzer Generator'. It recognizes regular expressions, and generates simple output based on what it is fed. -

- Effectivly, a bar code that links to a web page. Some camera phones have this ability. Remember the cuecat? That was a bar code scanner that you were supposed to use while reading magazines. That died a well deserved early death, but perhaps this makes a little more sense. -

- The most common answer to any question that involves network backup: http://www.amanda.org/ I still prefer Microlite Edge, though. -

- Microsoft's internal name for its Digital Rights Management Software. Janus was the two faced god, looking both front and back at the same time. Microsoft chose this because the likeness of Janus was often placed at doors as a symbolic guard. -

- A named pipe: write to it with one or more processes, read to it with another. All sorts of neat things become easier with a fifo. -

- Lightweight Directory Access Protocol. Even Microsoft uses LDAP (though they mucked it up, of course). -

- Pronounced 'Zammel', this is Microsoft's next development language, slated to appear with Longhorn. If you are an anti-Microsoft zealot, this is scary stuff. Yes, of course I'm an anti-Microsoft zealot.. -

- One some OSes, this is a 'parallel kill' that will use rsh to kill processes on multiple machines. On Linux and BSD, it allows selection by various criteria, including names (like 'killall'). -

- If you hear this, you are hearing an Apple person. The Finder is Mac's equivalent to Windows 'My Computer' - except, well it's different. -

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