ThinClientHowto

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What is a Thin Client? 什么是瘦客户机？

To the user, a thin client behaves like a regular desktop computer. To the administrator, a thin client has no storage of its own, is easy to maintain, and can give the user a modern computing experience even with ancient hardware.

对于终端用户来说，瘦客户机和平常使用的计算机没有什么区别；对于管理员来说，一个瘦客户机是没有本机存储设备，易于管理，利用陈旧计算机硬件为用户提供先进的计算体验的设备。

How do thin clients work? 瘦客户机终端如何工作？

Thin clients are computers that load and run most of their programs from a central server, but are displayed on the thin client's screen. In more technical terms, the thin client can either obtain a kernel from local storage, or load the kernel across the network. (Using these instructions, you will collect the linux kernel from the server using a bootable network card. This way, the thin client needs no more storage than the boot rom built into a bootable network card.)

瘦客户机终端从中央服务器下载要运行的程序, 运行并显示在本地屏幕上。用更确切的技术术语来说，就是客户端可以从本机存储器获得内核，或者通过网络下载内核来运行(通过可网络启动的网卡从服务器获取linux内核到本地。这样一来，瘦客户机终端就可以通过可网络启动的网卡获取内核到本地内存运行，而不需要其他额外的存储设备)。

Boot sequence 启动步骤

The PXE network card makes a DHCP request on the local network. The DHCP reply gives information to the card where to collect the linux kernel from. The kernel is collected over the network through the TFTP protocol.

启动时，网卡通过PXE协议向本地网络发出DHCP请求,网络中服务器响应此DHCP请求，并在此响应信息中指定何处去获得linux内核。然后linux内核通过TFTP协议从服务器端传输到客户端。

Once the kernel has been collected via TFTP, the kernel is executed; the machine boots linux. A initramfs collected with the linux kernel is mounted as a root file system. This carries and autodetect the necessary drivers for the network card, mouse, keyboard sound etc. Once the network card driver is loaded, a second DHCP request tells the client it's ip address, netmask, gateway, DNS server, and root NFS (Network File System) mount point.

一旦linux内核通过TFTP下载到客户端，内核解压并开始运行；客户端开始运行于linux上，initramfs作为根文件系统被mount上，它将自动查找和匹配相应的网卡，鼠标，键盘，声卡等设备的驱动，初始化一个系统的环境。一旦网卡驱动加载，第二次的DHCP请求发出获得的响应信息告知客户端将被分配的IP地址，子网掩码，默认网关，DNS服务器地址以及root NFS(网络文件系统)的挂载点。

The linux kernel runs the ubuntu initramfs, which mounts the root NFS share from the server onto the thin client read-only. The thin client now has a booted linux kernel, and a root file system, much like any Linux system. From now on, when we talk of the root file system on the client, we are actually talking about a root file system mounted read-only from the server. The root file system mounted by the thin client is not the same root file system the server itself uses, but is specially prepared for thin clients, and is shared by all thin clients connected to the server (located in /opt/ltsp/<arch> on the server) . The initramfs calls the init program, the Xserver settings are autodetected and the ubuntu breezy ltsp login manager, called ldm is started.

X nuts and bolts

After logging in, ldm starts a ssh tunnel and executes a X session on the server which is displayed through the tunnel on the thin clients X server. Using ssh here has the big advantage that you dont need to have a Xserver configured on the client and no unsafe tcp X transport is initialized like it was done in older days of ltsp.

Requirements

You will need:

  • An Ubuntu 5.10 system to be the server
  • At least one PXE-bootable system to be a client
  • A bunch of disk space
  • A fast network connection, or a local Breezy mirror, or some patience
  • A DHCP server which is capable of supporting PXE clients, or a separate network segment where you can run a dedicated DHCP server
  • Command-line familiarity
  • A sense of adventure
  • A burning desire to send feedback to ubuntu-devel

Warnings

  • Please don't use this Howto if you installed Edubuntu from CD, since the Installer does nearly all of the work described here already, if you use Edubuntu, follow the EdubuntuInstallNotes wikipage.
  • This is not the latest stable release of LTSP (4.1) but the new upcoming standard for LTSP (upstream codename MueCow). Since it is a very young implementation not all LTSP 4.1 options are supported (see [EdubuntuLtsConfParams] for details), nontheless you can use most solutions (like local device support or sound etc.) provided at http://wiki.ltsp.org. For some of the features that are planned/being worked on for default integration see:
    • ThinClientAudioSupport
    • ThinClientFasterStartup
    • ThinClientLocalDevices
    • ThinClientLocalDevicesForwardConnection
    • ThinClientMemoryUsage
  • Do not use the tools ltspadm and ltspcfg with this implementation of LTSP, it will for sure ruin the ltsp setup !!!

Getting Started

NOTE: If you plan to use the server as gateway/nat/firewall machine, it is strongly suggested to configure all the network interfaces before proceeding with the following steps.

  • Set up the DHCP server
    • If you have an existing DHCP server which can support PXE clients:
      • Configure it to pass a boot filename of `/ltsp/pxelinux.0` and a root path of `/opt/ltsp/i386`
      • For ISC DHCPD, use the following options:
filename "/ltsp/pxelinux.0";
option root-path "/opt/ltsp/i386";
      • Install `ltsp-server` on the server:
sudo apt-get install ltsp-server
    • If you want to run a dedicated DHCP server on the thin client server:
      • Install `ltsp-server-standalone` on the server:
sudo apt-get install ltsp-server-standalone
      • If necessary, customize `/etc/ltsp/dhcpd.conf` (by default it's configured for a server at 192.168.0.1 serving PXE clients)
      • If you are running a firewall on the server, you'll need to open TFTP and NFS (and DHCP if you're running the standalone server). Also, make sure portmap isn't limited to the loopback interface in /etc/default/portmap (comment out the line with "-i 127.0.0.1") if it exists, could be a leftover from Hoary. You also may want to edit `/etc/hosts.allow' and limit access for portmap, rpc.mountd, rpc.statd, and in.tftpd to the local network:
portmap:    192.168.0.0/24
rpc.mountd: 192.168.0.0/24
rpc.statd:  192.168.0.0/24
in.tftpd:   192.168.0.0/24
      • Restart the nfs subsystem:
sudo invoke-rc.d nfs-kernel-server restart
sudo invoke-rc.d nfs-common restart
sudo invoke-rc.d portmap restart
  • Build the thin client runtime environment:
sudo ltsp-build-client
    • This script is hardcoded to use a particular Ubuntu mirror, so you may wish to edit it if you have a nearby mirror or CD (sudo ltsp-build-client --mirror file:///cdrom), remember to copy sources.list from the server into the chroot)
    • If you changed your aptitude dependency-settings not to select recommended packages automatically, not all required packages will be downloaded and installed by this script. Then no login with sdm is possible for example because some parts of the x-server are missing
sudo apt-get install openssh-server
sudo ltsp-update-sshkeys
    • Check `/opt/ltsp/i386/etc/ssh/ssh_known_hosts` and ensure that your host key is associated with your host's IP address. Depending on your `/etc/hosts` configuration, this may not always be correct automatically (yet). If it looks like this:
servername ssh-rsa AAAAB3NzaC1yc2EAAAABI...
    • then add the IP address like this:
servername,192.168.0.1 ssh-rsa AAAAB3NzaC1yc2EAAAABI...
    • AND file a bug in Malone. THIS SHOULD NOT HAPPEN.
sudo invoke-rc.d dhcp3-server start
  • Optionally, create `/opt/ltsp/i386/etc/lts.conf`. If you don't create one, reasonable defaults and auto-detected values will be used. Note: Not all options are supported (see [EdubuntuLtsConfParams]).
  • PXE boot the client and see what happens. If all goes well, you should see a graphical login dialog.
  • If your client doesn't have PXE on the network card, you can generate a custom boot CD or floppy at ROM-o-matic.net. Burn the iso or floppy image and boot from that.
  • Log in, with any user authorized to login remotely via ssh, and see what happens. If all goes well, you should get a working desktop session on the server.
  • Send mail to ubuntu-devel with your findings

Tips

If you have a separate DHCP that you do not want to install LTSP on you can just redirect the thin-client to boot off a different server.

In your DHCP server's dhcpd.conf: 

next-server 192.168.0.3;
  • where 192.168.0.3 is the address of your LTSP server

Bugs

  • Bug 19407: Open``SSH doesn't appear to release ports used for X forwarding in a timely manner, preventing you from logging out and logging back in immediately when IPv6 support is enabled. Disable it by adding "Address``Family inet" to /etc/ssh/sshd_config, and restarting the openssh daemon.

Extras

  • 文章来源：官方WIKI
    翻译人员：freet15
    校对人员：
    文章状态：翻译中
取自“https://wiki.ubuntu.org.cn/index.php?title=ThinClientHowto&oldid=21187”