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Brand new to CentOS, and I'm certainly no Linux sysadmin, but I'm trying to setup a 'remote connection' (LAN only) to a brand new CentOS 7 install (for completion, I will connecting from a windows box using VNC Viewer).
There seems to be some major changes from CentOS 6 to CentOS 7 (my current installation, with GNOME), judging by most of the information I've found via googling-- including several changes on this very topic, hence this post to help clear up confusion. Even the information on the CentOS wiki seems not to match my experience with 7, so I can only assume it's out of date.

Screens Connect is a free utility that lets you connect back to your Mac or Windows PC from anywhere in the world. Download Screens Connect 4 (macOS 10.11 or later) Screens. In computing, Virtual Network Computing (VNC) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer.It transmits the keyboard and mouse events from one computer to another, relaying the graphical-screen updates back in the other direction, over a network. VNC is platform-independent – there are clients and servers for.

There is some form of screen sharing (as it is called..looking at the repos, it seems to be a minimal version of tigervnc --but I could be wrong on that!) built in to CentOS 7 (so it seems redundant, counter-productive & possibly a source of issues, to install a separate VNC/remote desktop server, as many guides suggest) :
The build in solution can be found by opening settings (click on the username in the top right to open a menu) --> Sharing (towards the bottom of that page) --> screen sharing
Mine is currently set to 'stupidly promiscuous mode' (no password, accept all connections) for testing, and will be changed once I make a connection.
Despite this service being enabled, VNC Viewer is not seeing anything (timing out)
I eventually stumbled onto a firewall, and changed those settings to allow VNC-Server through. (You'd think there'd be some mention of that when you enable the service). And that seems to have helped, as it changed the error from 'machine not found' to 'Unable to connect to VNC Server using your chosen security settings'. Except the default setting is 'Let VNC Server choose' and i've tried 'Prefer off' with the same success as well.
It's unclear to me why VNC Viewer cannot connect to my CentOS box..is there another service interfering..is there more I need to do with the firewall..is 'screen sharing' have some known issue I can't find.. Thanks to everyone who answers and I appreciate the help I advance.
Point of interests:
*Both machines are running on bare metal, I'm having enough problems without involving VMs (at the moment) thanks :p
*I used the full CentOS installation with default (GNOME?) desktop. I can double check if it's that important.
*Despite the prompts in CentOS, I CANNOT connect using my machine name as the VNC Viewer (in fairness, I can't connect at all) as I get a no server found error using the machine name, whereas IP seems to at least find the Machine/Service. Not sure why there is a discrepancy
*I have two users on my CentOS box, one admin, one standard user. The Standard user logs-in by default but both accounts have passwords.
*If this ends up being some form of extended firewall issue, would I be better off just turning the CentOS firewall off altogether? As this machine is on a trusted network & behind a router with a firewall anyway..

In computing, Virtual Network Computing (VNC) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer. It transmits the keyboard and mouse events from one computer to another, relaying the graphical-screen updates back in the other direction, over a network.^[1]

VNC is platform-independent – there are clients and servers for many GUI-based operating systems and for Java. Multiple clients may connect to a VNC server at the same time. Popular uses for this technology include remote technical support and accessing files on one's work computer from one's home computer, or vice versa.

VNC was originally developed at the Olivetti & Oracle Research Lab in Cambridge, United Kingdom. The original VNC source code and many modern derivatives are open source under the GNU General Public License.

There are a number of variants of VNC^[2] which offer their own particular functionality; e.g., some optimised for Microsoft Windows, or offering file transfer (not part of VNC proper), etc. Many are compatible (without their added features) with VNC proper in the sense that a viewer of one flavour can connect with a server of another; others are based on VNC code but not compatible with standard VNC.

VNC and RFB are registered trademarks of RealVNC Ltd. in the US and some other countries.

History[edit]

The Olivetti & Oracle Research Lab (ORL)^[3] at Cambridge in the UK developed VNC at a time when Olivetti and Oracle Corporation owned the lab. In 1999, AT&T acquired the lab, and in 2002 closed down the lab's research efforts.

Developers who worked on VNC while still at the AT&T Research Lab include:^[4]

• Tristan Richardson (inventor)
• Andy Harter (project leader)
• James Weatherall

Following the closure of ORL in 2002, several members of the development team (including Richardson, Harter, Weatherall and Hopper) formed RealVNC in order to continue working on open-source and commercial VNC software under that name.

The original GPLed source code has fed into several other versions of VNC. Such forking has not led to compatibility problems because the RFB protocol is designed to be extensible. VNC clients and servers negotiate their capabilities with handshaking in order to use the most appropriate options supported at both ends.

As of 2013, RealVNC Ltd claims the term 'VNC' as a registered trademark in the United States and in other countries.^[5]

Etymology[edit]

The name Virtual Network Computer/Computing (VNC) originated with ORL's work on a thin client called the Videotile, which also used the RFB protocol. The Videotile had an LCD display with pen input and a fast ATM connection to the network. At the time, network computer was commonly used as a synonym for a thin client; VNC is essentially a software-only (i.e. virtual) network computer.^{[citation needed]}

Operation[edit]

• The VNC server is the program on the machine that shares some screen (and may not be related to a physical display – the server can be 'headless'), and allows the client to share control of it.
• The VNC client (or viewer) is the program that represents the screen data originating from the server, receives updates from it, and presumably controls it by informing the server of collected local input.
• The VNC protocol (RFB protocol) is very simple, based on transmitting one graphic primitive from server to client ('Put a rectangle of pixel data at the specified X,Y position') and event messages from client to server.

In the normal method of operation a viewer connects to a port on the server (default port: 5900). Alternatively (depending on the implementation) a browser can connect to the server (default port: 5800). And a server can connect to a viewer in 'listening mode' on port 5500. One advantage of listening mode is that the server site does not have to configure its firewall to allow access on port 5900 (or 5800); the duty is on the viewer, which is useful if the server site has no computer expertise and the viewer user is more knowledgeable.

The server sends small rectangles of the framebuffer to the client. In its simplest form, the VNC protocol can use a lot of bandwidth, so various methods have been devised to reduce the communication overhead. For example, there are various encodings (methods to determine the most efficient way to transfer these rectangles). The VNC protocol allows the client and server to negotiate which encoding they will use. The simplest encoding, supported by all clients and servers, is raw encoding, which sends pixel data in left-to-right scanline order, and after the original full screen has been transmitted, transfers only rectangles that change. This encoding works very well if only a small portion of the screen changes from one frame to the next (as when a mouse pointer moves across a desktop, or when text is written at the cursor), but bandwidth demands get very high if a lot of pixels change at the same time (such as when scrolling a window or viewing full-screen video).

VNC by default uses TCP port 5900+N,^[6][7] where N is the display number (usually :0 for a physical display). Several implementations also start a basic HTTPserver on port 5800+NDreams casino mobile. to provide a VNC viewer as a Java applet, allowing easy connection through any Java-enabled web-browser. Different port assignments can be used as long as both client and server are configured accordingly. A HTML5 VNC client implementation for modern browsers (no plugins required) exists too.^[8]

Although possible even on low bandwidth, using VNC over the Internet is facilitated if the user has a broadband connection at both ends. However, it may require advanced NAT, firewall and router configuration such as port forwarding in order for the connection to go through. Users may establish communication through Virtual Private Network (VPN) technologies to ease usage over the Internet, or as a LAN connection if VPN is used as a proxy, or through a VNC repeater (useful in presence of a NAT).^[9][10]

Xvnc is the Unix VNC server, which is based on a standard X server. To applications, Xvnc appears as an X 'server' (i.e., it displays client windows), and to remote VNC users it is a VNC server. Applications can display themselves on Xvnc as if it were a normal X display, but they will appear on any connected VNC viewers rather than on a physical screen.^[11] Alternatively, a machine (which may be a workstation or a network server) with screen, keyboard, and mouse can be set up to boot and run the VNC server as a service or daemon, then the screen, keyboard, and mouse can be removed and the machine stored in an out-of-the way location.

In addition, the display that is served by VNC is not necessarily the same display seen by a user on the server. On Unix/Linux computers that support multiple simultaneous X11 sessions, VNC may be set to serve a particular existing X11 session, or to start one of its own. It is also possible to run multiple VNC sessions from the same computer. On Microsoft Windows the VNC session served is always the current user session.^{[citation needed]}

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Users commonly deploy VNC as a cross-platform remote desktop system. For example, Apple Remote Desktop for Mac OS X (and more recently, 'Back to My Mac' in 'Leopard' - Mac OS X 10.5) interoperates with VNC and will connect to a Unix user's current desktop if it is served with x11vnc, or to a separate X11 session if one is served with TightVNC. From Unix, TightVNC will connect to a Mac OS X session served by Apple Remote Desktop if the VNC option is enabled, or to a VNC server running on Microsoft Windows.^[12]

In July 2014 RealVNC published a Wayland developer preview.^[13][14]

Security[edit]

By default, RFB is not a secure protocol. While passwords are not sent in plain-text (as in telnet), cracking could prove successful if both the encryption key and encoded password were sniffed from a network. For this reason it is recommended that a password of at least 8 characters be used. On the other hand, there is also an 8-character limit on some versions of VNC; if a password is sent exceeding 8 characters, the excess characters are removed and the truncated string is compared to the password. https://site-download.mystrikingly.com/blog/filezilla-server-mac-alternative.

UltraVNC supports the use of an open-source encryption plugin which encrypts the entire VNC session including password authentication and data transfer. It also allows authentication to be performed based on NTLM and Active Directory user accounts. However, use of such encryption plugins makes it incompatible with other VNC programs. RealVNC offers high-strength AES encryption as part of its commercial package, along with integration with Active Directory. Workspot released AES encryption patches for VNC. According to TightVNC,^[15] TightVNC is not secure as picture data is transmitted without encryption. To circumvent this, it should be tunneled through an SSH connection (see below).

VNC may be tunneled over an SSH or VPN connection which would add an extra security layer with stronger encryption. SSH clients are available for most platforms; SSH tunnels can be created from UNIX clients, Microsoft Windows clients, Macintosh clients (including Mac OS X and System 7 and up) – and many others. There are also freeware applications that create instant VPN tunnels between computers.

An additional security concern for the use of VNC is to check whether the version used requires authorization from the remote computer owner before someone takes control of their device. This will avoid the situation where the owner of the computer accessed realizes there is someone in control of their device without previous notice.

See also[edit]

References[edit]

1. ^Richardson, T.; Stafford-Fraser, Q.; Wood, K. R.; Hopper, A. (1998). 'Virtual network computing'(PDF). IEEE Internet Computing. 2: 33–38. CiteSeerX10.1.1.17.5625. doi:10.1109/4236.656066.
2. ^The VNC family of Remote Control Applications: a list of VNC variants
3. ^'VNC Frequently Asked Questions (FAQ)'. 1999. Archived from the original on 15 August 2000.
4. ^RealVNC Executive Profiles
5. ^Copyright and trademarks RealVNC. Accessed Feb 23, 2018.
6. ^'RealVNC - Frequently asked questions'.
7. ^'UltraVnc Configuration'.
8. ^'noVNC'.
9. ^'OpenWRT VNC repeater'.
10. ^'uVNC repeater'.
11. ^AT&T Laboratories Cambridge (1999). 'X-based VNC server'. Virtual Network Computing. Archived from the original on 19 March 2007. Retrieved 24 March 2007.
12. ^'OnlineVNC Server for Windows OSes'.
13. ^'VNC® Wayland Developer Preview'. 8 July 2014. Archived from the original on 14 July 2014. Retrieved 10 July 2014.
14. ^'RealVNC Wayland developer preview email'. freedesktop.org. 9 July 2014.
15. ^How secure is TightVNC? TightVNC Frequently Asked Questions. TightVNC.com Accessed Feb 23, 2018

External links[edit]

Screens 4 Vnc Remote Desktop Screen Sharing 4 0 2017

Wikimedia Commons has media related to VNC.

Screens 4 Vnc Remote Desktop Screen Sharing 4 0 2013

Wikibooks has a book on the topic of: Internet Technologies/VNC

• AT&T VNC - Original AT&T-Cambridge VNC website

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