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Having difficulty with UNIX concept. Please help!

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Old Unix and Linux 01-10-2007   -   Original Discussion by ALon
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Having difficulty with UNIX concept. Please help!

Hi,

I would be very happy if someone could help me please. I am relatively new to UNIX, and still learning.

My understanding of things are:
Say I have a PC running Windows. This machine has a name. If I have 10 PC's, then I have 10 names, one for each PC. Each PC is independent of the other. It is a separate entity. Each has it's own file system, CPU, RAM, harddrive etc...

Now, considering UNIX...
At university there are about 50 machines in the lab. Each is a box, with a label on it stating its hostname e.g abc.def.ac.uk.
So I am assuming that each is a machine in its own right, yes? i.e. if we were to open the box, inside each machine will have its own CPU, own RAM, own motherboard etc. Is this correct?
Now how does the UNIX bit come in? It says that UNIX is supposed to be "multi user, multi tasking, time sharing". Does this simply mean that some other user too can remotely log into that box and use it to do their work?

Now for the other question. If I sit at machine 1, and create a file, and then I log out, and log in on machine 5, then that file is visible. Does this mean that when I created that file, it was not created on the harddrive of machine 1, but rather on a big hard drive inside the server room?

So, I am very confused here. There seem to be many directory structures, one somewhere in a server room which stores everything, and one on each box where the UNIX O/S is stored.

Someone please address what I am asking using simple, laymen terms.

Thanks a lot.

A

Last edited by ALon; 01-10-2007 at 05:08 PM..
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Old Unix and Linux 01-10-2007   -   Original Discussion by ALon
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Wow… I’m not sure where to start here…
Yes unix is multi tasking. User's can log into one box and using a variety of tool/apps work or store their information on another box. The name on the box is most likely a “hostname”. So to move (not physically) to another box you could "telnet" to box 3 and use your login in there (assuming you have a login there) even though you’re still at box 1. Maybe someone can suggest a beginning UNIX book or just do some google searches on client/server definitions and relationships.

For your second question, the admin there most likely has your login set up to point to a common storage space so any machine can access files. It makes it easier to manage and more efficient. If you think of one box as a single stand alone entity you’re missing the whole networking picture.
hth's
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Old Unix and Linux 01-10-2007   -   Original Discussion by ALon
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Thank you very much for your reply. It makes a little more sense now. I do understand the way client/server architectures work, I am just not sure how UNIX works...I tried reading wikipedia, but it wasn't very helpful, for me anyway!

OK, if I an on machine1, and want to access the harddrive on machine3, does that mean I have to mount the filesystem of machine3 onto machine1? Or something along those lines.

You mentioned hostnames. Is a hostname simply the name of a unix box? Does it mean that each hostname has its own CPU, harddrive, RAM etc?

Thanks.
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Old Unix and Linux 01-11-2007   -   Original Discussion by ALon
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if you want to access data on particular HD, you can S/FTP the data, but if you need the entire HD onto your box ( where you are currently logged ) yes, you need to NFSmount this partition.
Hostname is a reference to a machine unique name, e.g.
1 - mainframe.sysgate.org
2 - sysadmin.sysgate.org
These would be two different machines, each with CPU, Ram, etc, but still part of domain "sysgate.org"
Hope this helps.
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Old Unix and Linux 01-11-2007   -   Original Discussion by ALon
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Quote:
Originally Posted by ALon
Now, considering UNIX...
At university there are about 50 machines in the lab. Each is a box, with a label on it stating its hostname e.g abc.def.ac.uk.
So I am assuming that each is a machine in its own right, yes? i.e. if we were to open the box, inside each machine will have its own CPU, own RAM, own motherboard etc. Is this correct?
Yes. They're ordinary computers running some variety of UNIX.
Quote:
Now how does the UNIX bit come in? It says that UNIX is supposed to be "multi user, multi tasking, time sharing". Does this simply mean that some other user too can remotely log into that box and use it to do their work?
If the machine is configured to allow this, then yes -- absolutely. The computers at my university had a similar arrangement which I often used for just that, though the university placed careful restrictions on who was allowed to login from where.

May I shift your perspective a little? Try imagining it, not as a "computer" in the Windows sense, but a machine that sits there and runs "jobs". When you run a program, that makes a new job, and you can have many jobs running at the same time belonging to many different users. It keeps careful track of which users are allowed to run which jobs and access which files but beyond that, the fact that you're the one sitting in the chair in front of it is largely incidental. You could remove the keyboard and monitor and just use it completely remotely -- I do for my UNIX machine, which is handy since it's a web server hundreds of kilometers away from me.
Quote:
Now for the other question. If I sit at machine 1, and create a file, and then I log out, and log in on machine 5, then that file is visible. Does this mean that when I created that file, it was not created on the harddrive of machine 1, but rather on a big hard drive inside the server room?
Quite probably.
Quote:
So, I am very confused here. There seem to be many directory structures, one somewhere in a server room which stores everything, and one on each box where the UNIX O/S is stored.
UNIX does not have drive letters, as you may have noticed. Instead it has one(one per computer!) giant directory tree starting from one "root partition" -- that's going to be the hard drive of the computer you're sitting at -- and attaches or "mounts" more drives to different directories. Usually, the /etc/fstab file tells a UNIX computer which drives to attach where, when. Also try 'df' in a shell to show you what disks are mounted where at that particular moment.

I've seen something like your setup before. How it works is, each individual computer has it's own independent disk space used for system files(stored on it's root partition), so it can boot up independently. But the directories you use, something like /home/username/, get "mounted" to the big server through the network. When you login, do things, and logout, you're running programs on that particular machine, but all your data and settings gets saved to the server. So no matter which one you login to, you get the same files and settings.

Last edited by Corona688; 01-11-2007 at 12:11 PM..
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