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Hi Experts, I am new in linux....I am eager to know about Linux functionality Everyone says that Linux is Multi User Operating system. How ? I heard that linux can ...
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  1. #1
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    How linux is Multi-user OS ?


    Hi Experts,

    I am new in linux....I am eager to know about Linux functionality
    Everyone says that Linux is Multi User Operating system. How ?

    I heard that linux can login only 7 or 12 Maximum user at
    same time. it depend on Clrl + Alt + F1 to 12 ??
    Am i right ?

    Somebody says linux can handles 65.000 users for 2.4 kernels, and 4 billion for 2.6 kernels... i am very confuse in this Topic so
    please help me ?

  2. #2
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    Hi,
    Firstly let me say I'm not an expert in the sense of "linux guru" but I have been fiddling around with this O/S for around 20 years. For the past 10 years or so I have only used other O/Ss when I don't have a choice.

    In the dark ages (pre 1995) the fact that linux was multi-user simply meant you could specify more than one login and they would not interfere with another. It didn't necessarily mean you could simultaneously login (that's a hardware factor). It was none-the-less a big advantage over windoze.

    Since the early days things have developed dramatically, however, the number of users issue still causes a good deal of discussion, see this forum discussion for instance. Once again it is not the total number of simultaneous users that is refered to here.

    The number of users on the system can be limited by certain settings (you need admin privileges). I found some info on this at linuxtopia.

    Hope that gives you a lead-in to the topic.

    Cheers
    Achim

  3. #3
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    Hi

    Multi-user means basically that. That many users could be logged on a system at the same time.

    In the dark ages, as akim_59 says there were big mainframes running Unix and many users conected to them using terminals, both in character and graphics mode. As Linux is a Unix derivative, it has the same capability.

    You can have a PC or a dedicated server acting as the "mainframe" or terminal server and use other PC in the network to conect to it.

    Also a very simple use of this is when you use telnet or ssh to connect to a pc or server.

    There are several project that make use of this capability to allow many PC, usually with very low specs to act as terminals to a server and use the speed , memory and CPU power of the server. For example Linux Terminal Server Project - Welcome to LTSP.org

    Usually the limiting factors about how many users can work "comfortably" conected to a server are RAM memory and CPU Power of the terminal server.

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    Quote Originally Posted by ift38375 View Post
    Hi Experts,

    I am new in linux....I am eager to know about Linux functionality
    Everyone says that Linux is Multi User Operating system. How ?

    I heard that linux can login only 7 or 12 Maximum user at
    same time. it depend on Clrl + Alt + F1 to 12 ??
    Am i right ?

    Somebody says linux can handles 65.000 users for 2.4 kernels, and 4 billion for 2.6 kernels... i am very confuse in this Topic so
    please help me ?
    If you are looking at using the Ctrl+Alt+Fn for multiple users, then you are only one user at a time (with multiple users logged in). Right now there are 42 people logged into my notebook and all are using the GUI (although most are not using a desktop). How do I know how many people are logged in (in one ssh session, I am logged in as root and I run the command:
    Code:
    who | wc -l
    And it is returning a 42 count. If I run the command:
    Code:
    who
    I see that everyone of them is using the GUI layer as they have the "DISPLAY" defined (or are using X-Forwarding via their ssh connection).

  6. #5
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    Quote Originally Posted by achim_59 View Post
    In the dark ages (pre 1995) the fact that linux was multi-user simply meant you could specify more than one login and they would not interfere with another. It didn't necessarily mean you could simultaneously login (that's a hardware factor). It was none-the-less a big advantage over windoze.
    Not true, I have been logging into Linux boxes via a telnet session over ethernet (TCP) connection since the kernel was at 0.98 (back in the early 1990) I had to by a good X-Server so that the GUI would run across the network. In the Unix world, the display has been able to be sent to another machine since the early 1970s.

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    The control - alt thing just starts extra virtual console windows on your computer, each with its own command shell.

    Yes, you could have 7 or 12 friends with accounts on your box all log in one per virtual screen, but unless you and your friends all want to share one screen and keyboard then they will need to remote in over a network connection (telnet or ssh as others have mentioned).

    The control alt thing is really handy if you have no graphics environment running, so for example you could have one session running as "root" and one as yourself and flip back and forth between them. Or you can open one long slow job (downloading a DVD for example) in one console and then flip to another and log in to do something else.

    Or you could set up a bank of dialup modems and let lots of people connect. I ran the servers for an internet service provider for a few years. We had (I forget the exact number now) probably 32 modems on one Pentium class server. (That's just "Pentium" with no numbers after it.) It worked fine. Every user got a shell account and used PPP for Internet access. So connecting over the Internet meant you were "logged in" to the server even if you did not open a shell window and type commands.

    The practical limits on how many people can use a Linux box at once are determined by how much of the resources are used up by what people are doing. So for example, you could easily have 20 people logged in all reading their email at the same time and no one would notice any perceptible lag. But if you had 19 programmers all doing builds at the same time, the 1 who was trying to write code in an editor would complain. (Builds use lots of disk i/o and lots of CPU.)

    In other words, you are limited by resources like how much memory is available and how fast your CPU and hard drives are.

    You can tune a lot of system settings (see 'sysctl') to make a Linux server perform better for different applications. For example you can adjust the number of files that can be open at the same time. There are also per-user limits you can apply.

    ANYWAY. If you want to try it out, I'd suggest you install an SSH server and start it running. Then go to another computer and install an SSH client and run it. Log in to the server. Roughly for Debian/Ubuntu you'd do this

    on the server ---
    sudo apt-get install openssh-server
    sudo service ssh start

    on the client ----
    sudo apt-get install openssh-client
    ssh yourusername@IP_ADDRESS_OF_SERVER

    Then you should get a password prompt from the server...

    Your second computer does not have to run Linux, Mac's already have the ssh client installed. From a Windows box I usually download and install "putty".

    If you ssh from a Mac or Linux box to a Linux server you can pass the DISPLAY setting through too, typically by adding -Y to the command line like "ssh -Y myname@server" and then you can run graphical programs so for example you could type "firefox" to run a copy of firefox browser on "server" and have its graphics show up on your local computer.

    Hope this helps

    Brian

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    Hello Everyone,

    I am confuse with maximum limit of user login with Linux OS.
    is it depends on 12 Virtual terminals like as Ctrl+Alt+F1 to 12 or Else ?

    I heard that 12 Virtual teriminals is thing of Single user convenience who is
    sitting on Linux PC. Does it make any sense ? How can single user use all
    Virtual terminal at once ?

    Second Question, If we talk about Multi-User Functionality of Linux then
    what kind of work can perform by multiple remote users? Plz give me one example.

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    Smile

    I log in to various Linux systems frequently, using ssh. I have around 8 Linux systems on a LAN. For example, I can ssh into the same system from all 6 virtual terminals of one other system, or I can ssh to that same system from all the other systems. In either case, there would be half a dozen user logins on that first system.

    In order to log to a system with ssh, it's necessary to install an ssh daemon program, such openssh-server. Most Linux distros don't install an ssh daemon by default, so you have to install it explicitly. I don't want to allow telnet, so I never install telnetd. Ssh is more secure. However I do have my router set up to allow ssh from the Internet to one of my machines.

    For copying files over the Internet, I use scp.

    My ISP uses RedHat Linux - at the moment, it has 50 users logged in, most of them using ssh to connect to the shell server, and about half a dozen logging in from other systems in their building. I used the shell commands

    $ who | wc -l

    to see that.

    At the moment, my main home server - the one connected to the Internet - has two users:

    I am logged in to it from my XFCE console, and I'm logged in from this netbook over my LAN,using ssh.

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    Let me try to sum it for you. Linux has many ways to connect multiple users, as shown by the other posts here.

    If you are trying to equate to how Windows does multi-user, where more than 1 user is logged into the console, each with their own desktop, and switching between them without logging off, then you are looking for the "Switch User" option under the Gnome desktop. KDE likely supports this, too, but I am not sure what it is called. I am not sure how many users are allowed to log in one time, but since, like Windows, all users must share one keyboard, mouse and monitor, how many are really practical? 3 or 4? Certainly not more than 12, right?

    If you are talking about text console sessions, then as mentioned above, up to 12 virtual consoles can be logged on at one time, but the user can only see 1 of them at a time, and the user switches between virtual consoles using Ctrl-Alt-Fnn. Different users can log onto each virtual console.

    If you are talking about connecting via network, well then, a whole bunch of other options are available.

    You can configure X-Windows to accept network connections, and then 1000's of users can log onto one system using Xnest, or Xephyr, or X-Windows itself. These type of connections are like Windows RDP sessions, although these are only practical on a LAN.

    For WAN Desktop connections, there is NX Machine, that uses X-Windows, but provides caching, compression, and encryption via ssh for Internet connection Desktops. Again, this is like multiple RDP sessions.

    Another option for remote desktops is using VNC server/client connections.

    If you only need to connect to a text session, then, as velikij says, ssh is the connection of choice. Telnet use is discouraged due to its insecurity, but if you are connecting from a stock Windows system, this is your only choice, as Windows is only modern OS that doesn't include a ssh client.

    As to the total number of users, your numbers are more or less correct, 4 billion unique users are supported by 2.6+ kernels, but your average PC is not going be able to support that many users at once. The real limit as to how many users can be logged on at once is a function of connection type (GUI or text), what programs the users will be using, and the systems's resources (# threads, RAM, etc.). A lot of users (like 100's) can log on and do text data entry, but only a few will be able to do 3D-CAD at once.

    This list is by no means complete as to possible connections types. That is one of the beauties of Linux, the possiblities are almost endless.
    If you want a specific example, you will need to tell us what kind of mutil-user access you are looking for.

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    Wink You make my point for me

    Quote Originally Posted by alf55 View Post
    Not true, I have been logging into Linux boxes via a telnet session over ethernet (TCP) connection since the kernel was at 0.98 (back in the early 1990) I had to by a good X-Server so that the GUI would run across the network. In the Unix world, the display has been able to be sent to another machine since the early 1970s.
    This same question turned up in another forum - see here.

    As you state, the terminal data is sent by Linux "to another machine". This is precisely my point. You need external clients (Telnet, PuTTY, etc.) in order to have multiple logins simultaneously. Or has there been some new development?

    The dark ages I spoke of were the days when all you had at your disposal was a dumb terminal. I'm thinking of the glory days of the PDP-11 series and the not so glorious IBM 3270 .

    You are right to state that Linux client/server technology has been available pretty much since the start of the Linux O/S, though I wasn't involved with it back then.

    Achim

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