Mobaxterm gssapi - Free Activators
SERVICE ACTIVATION OPERATION USING MOBAXTERM APPLICATION AS THE SOLUTION, I HAVE GIVEN THE FOLLOWING p primary (0 primary, 0 extended, 4 free). mobaxterm script. A Use After Free: CWE-416 vulnerability In MobaXterm 11.1, the mobaxterm: URI Activation Kernel improperly handles an. RPC request.
Mobaxterm gssapi - Free Activators -
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VNC or Virtual Network Computing is a platform-independent protocol that enables users to connect to a remote computer system and use its resources from a Graphical User Interface (GUI).
It’s like remote controlling an application: the client computer’s keystrokes or mouse clicks are transmitted over the network to the remote computer. VNC also allows clipboard sharing between both computers. If you come from a Microsoft Windows server background, VNC is much like the Remote Desktop Service, except it’s also available for OS X, Linux, and other operating systems.
Like everything else in the networking world, VNC is based on the client server model: VNC server runs on a remote computer — your Droplet — which serves incoming client requests.
In this tutorial we will learn how to install and configure a VNC server on CentOS 7. We will install the TigerVNC server which is freely available from the TigerVNC GitHub repository.
To demonstrate how VNC works, we will also install the GNOME desktop on your CentOS server. We will create two user accounts and configure VNC access for them. We will then test their connectivity to the remote desktop, and finally, learn how to secure the remote connection through an SSH tunnel.
The commands, packages, and files shown in this tutorial were tested on a minimal installation of CentOS 7. We would recommend the following:
- Distro: CentOS 7, 64-bit
- Resource Requirements: A Droplet with 2 GB RAM
- To follow this tutorial, you should use a sudo user. To understand how sudo privileges work, you can refer to this DigitalOcean tutorial
Warning: You should not run any commands, queries, or configurations from this tutorial on a production Linux server. This could result in security issues and downtime.
Step 1 — Creating Two User Accounts
First, we will create two user accounts. These accounts will remotely connect to our CentOS 7 server from VNC clients.
Run the following command to add a user account for joevnc:
Then run the passwd command to change joevnc’s password:
The output will ask us for new password. Once supplied, the account will be ready for login:
Next, create an account for janevnc:
Set the password for janevnc:
Step 2 — Installing GNOME Desktop
Now we will install GNOME desktop. GNOME is a collaborative effort: it’s a collection of free and open source software that makes up a very popular desktop environment. There are other desktop environments like KDE, but GNOME is more popular. Our VNC users will use GNOME to interact with the server from its desktop:
Depending on the speed of your network, this can take a few minutes.
Once the package group is installed, reboot the server:
Troubleshooting — Server Stuck at Boot Phase
Depending on how your server has been set up, when the machine starts up it may remain in the boot phase showing a message like this:
To get past this, press 1 (license read), then 2 (accept licence), and then C (to continue). You may have to press C two or more times. The image below shows this:
If you don’t see this error and the boot process is smooth, all the better – you can move on to the next step.
Step 3 — Installing TigerVNC Server
TigerVNC is the software that will allow us to make a remote desktop connection.
Install the Tiger VNC server:
This should show output like the following:
Now we have VNC server and the GNOME desktop installed. We have also created two user accounts for connecting through VNC.
Step 4 — Configuring VNC Service for Two Clients
VNC server doesn’t start automatically when it’s first installed. To check this, run the following command:
The output will be like this:
You can also run this command:
This should show output like this:
So why is it disabled? That’s because each user will start a separate instance of the VNC service daemon. In other words, VNC doesn’t run as one single process that serves every user request. Each user connecting via VNC will have to start a new instance of the daemon (or the system administrator can automate this).
CentOS 7 uses the systemd daemon to initiate other services. Each service that natively runs under systemd has a service unit file that’s placed under the directory by the yum installer. Processes that get started automatically at boot time have a link to this service unit file placed in the directory.
In our case, a generic service unit file was created in the directory, but no link was made under . To test this, run the following commands:
You should see:
Then check under :
This one doesn’t exist:
So, the first step is to start two new instances of VNC server for our two users. To do this, we will need to make two copies of the generic VNC service unit file under . In the code snippet below, you’re making two copies with two different names:
So why did we add two numbers (along with the colon) in the copied file names?
Again, that comes back to the concept of individual VNC services. VNC by itself runs on port 5900. Since each user will run their own VNC server, each user will have to connect via a separate port. The addition of a number in the file name tells VNC to run that service as a sub-port of . So in our case, joevnc’s VNC service will run on port 5904 (5900 + 4) and janevnc’s will run on 5905 (5900 + 5).
Next edit the service unit file for each client. Open the file with the vi editor:
A look at the “Quick HowTo” section tells us we have already completed the first step. Now we need to go through the remaining steps. The comments also tell us that VNC is a non-trusted connection. We will talk about this later.
For now, edit the section of the file, replacing instances of with . Also, add the clause at the end of the parameter. This just tells VNC the screen size it should start in. You will modify two lines in total. Here’s what the edited file should look like (note that the entire file is not shown):
Save the file and exit vi.
Similarly, open the file in vi and make the changes for user janevnc:
Here’s just the section with the changes marked:
Next, run the following commands to reload the systemd daemon and also to make sure VNC starts up for two users at boot time.
Enable the first server instance:
Enable the second server instance:
Now you’ve configured two VNC server instances.
Step 5 — Configuring Your Firewall
Next, we will need to configure the firewall to allow VNC traffic through ports 5904 and 5905 only. CentOS 7 uses Dynamic Firewall through the firewalld daemon; the service doesn’t need to restart for changes to take effect.
The firewalld service should start automatically at system boot time, but it’s always good to check:
This should show:
If the state is “not running” for any reason, execute the following command to make sure it’s running:
Now add the rules for ports 5904 and 5905:
Reload the firewall:
Step 6 — Setting VNC Passwords
We are one step away from seeing VNC in action. In this step, the users will need to set their VNC passwords. These are not the users’ Linux passwords, but the passwords to log in to the VNC sessions.
Open another terminal connection to the CentOS 7 server, and this time log in as joevnc.
Execute the following command:
As shown in the output below, the server will ask joevnc to set up a VNC password. After typing in the password, the program also shows a number of files being created in the user’s home directory:
Let’s look at the line . localhost.localdomain was the server name in our example; in your case it could be different. Note the number after the server name: (1, separated by a colon). It’s not the number in joevnc’s service unit file (which was 4). That’s because this is the display numberjoevnc’s session will run on in this server, not the port number of the service () itself.
Next open a new terminal session and log in as janevnc. Here as well, start the VNC server and set a password for janevnc:
You should see similar output showing that janevnc’s session will run on display 2.
Finally, reload the services from the main terminal session:
Step 7 — Connecting to Remote Desktops with a VNC Client
For this tutorial, we will assume users joevnc and janevnc are trying to connect to the CentOS 7 server from their Windows computers.
They will each need a VNC client for Windows to log into the remote desktop. This client is just like a terminal client like PuTTY, except it shows graphical output. There are various VNC client available, but the one we will use is RealVNC, available here. VNC Viewer for Mac OS X is available for download on the same page, and the Mac version is fairly similar to the Windows one.
When VNC Viewer is started, it shows a dialogue box like this:
In the VNC Server field, add the IP address of your CentOS 7 server. Specify the port number 5904 after the server’s IP, separate by a colon (:). We used 5904 because that’s the VNC service port for joevnc.
We have also decided to let VNC Viewer choose the encryption method. This option will only encrypt the password sent across the network. Any subsequent communication with the server will be unencrypted. (We’ll set up a secure SSH tunnel in the final step.)
In fact, a warning message shows just that:
Accept the warning for now. A password prompt is displayed:
Enter joevnc’s VNC password that you set earlier.
A new window opens showing the GNOME desktop for our remote CentOS server:
Accept the default welcome message.
Now joevnc can start a graphical tool like the GNOME calculator:
You can leave this desktop connection open.
Now janevnc can also start another VNC session with the CentOS server. The IP address is the same, and the port is 5905:
When janevnc logs in via VNC Viewer, an empty desktop with a welcome message is shown, just like it was shown for joevnc. In other words, the two users are not sharing the desktop instances. joevnc’s desktop should still be showing the calculator.
To close the remote desktop session, simply closing the window will do. However, this doesn’t stop the user’s VNC service in the background on the server. If the service is not stopped or restarted and the machine had no reboots, the same desktop session would be presented at the next logon.
Close the VNC Viewer windows for joevnc and janevnc. Close their terminal sessions, too. From the main terminal window, check to see if the VNC services are still running:
The output shows that the remote desktop is still running:
Check the second service:
This one is running, too:
If you wanted to log back into joevnc’s desktop at this point, you’d see the same calculator app open.
This presents some interesting challenges for system administrators. If you have a number of users connecting to the server via VNC, you may want to devise some way to stop their VNC services when no longer needed. This may save some valuable system resources.
Troubleshooting — VNC Service Crashes
As you test and play around with VNC, you may sometimes find the service has crashed and is unrecoverable. When you try to check the status:
This long error message may come up:
Trying to start the service doesn’t work:
Usually the reason is simple enough. Check :
The related error will look like this:
The remedy is to delete the file under /tmp folder:
Then start the VNC service:
Although relatively rare, you may encounter other errors when working with VNC. For example, your remote desktop screen can go blank or hang, the session might crash with a cryptic error message, VNC Viewer may not connect properly or transmit commands to the GUI to launch applications, etc.
We recommend checking the file to get a better understanding. At times you may need to reboot your server, or in extreme cases recreate the VNC service.
System resources can also be a culprit; you may have to add extra RAM to your Droplet, etc.
Step 8 — Securing VNC Sessions through SSH Tunneling
So far both joevnc and janevnc have been accessing their remote desktops through unencrypted channels. As we saw before, VNC Viewer warns us about this at connection time; only the password is encrypted as the sessions begins. Any subsequent network traffic and data transfer is open for anyone to intercept in the middle.
About SSH Tunnelling
This is where Secure Shell (SSH) sessions can help. With SSH, VNC can run within the context of an SSH encrypted session. This is known as tunnelling. In effect, VNC traffic piggybacks on the SSH protocol, resulting in all of its communication with the server being encrypted. It’s called tunnelling because SSH is providing wraparound protection over VNC and VNC is running as if in a tunnel within SSH. SSH tunnelling can be used for other protocols like POP, X, or IMAP as well.
SSH tunnelling works with port forwarding which is basically a means of translating access from one particular port to a different port on another machine. With port forwarding, when a client application connects to Port A running on machine A, it’s transparently forwarded to port B running on machine B. The client application is unaware of this translation and thinks it’s connecting to the original port. Port forwarding is one of the features of SSH protocol.
For more detailed information about SSH tunneling, read this tutorial.
In this tutorial we have configured VNC to run on ports 5904 (for joevnc) and 5905 (for janevnc).
With port forwarding, we can set our local VNC client to connect to port 5900 on the local client computer, and this can be mapped to port 5905 on the remote server. This is example is for janevnc’s connection, but you could easily follow the same steps for any other clients.
When the VNC client application starts, it can be pointed to port 5900 on localhost, and our port forwarding will transparently transport it to port 5905 on the remote server.
Note: You’ll have to start an SSH section each time to make the connection secure.
On your Mac, open Terminal.
Enter the following connection information, being sure to replace with your remote server’s IP address:
Enter janevnc’s UNIX password. The connection will appear to hang; you can keep it running for as long as you use the remote desktop.
Now skip ahead to the VNC Viewer instructions.
For securing janevnc’s VNC session, we will assume the local Windows computer has PuTTY installed. PuTTY is free and can be downloaded from here.
If janevnc’s VNC and terminal sessions are not closed already, close them now.
Start PuTTY. In the session screen, ensure you specify the server IP address and give a descriptive name to the connection, then click the Save button to save the connection details. Note how we have specified in the Hostname field:
Next, expand the SSH menu item in the left navigation pane, and select the X11 item. This shows the X11 forwarding properties for the session. Ensure the checkbox for Enable X11 forwarding is checked. This ensures that SSH encrypts X Windows traffic that flows between the server and client:
Finally, select SSH > Tunnels. Type in the Source port field. In the Destination field, specify your server’s name or IP address, followed by a colon and the VNC port number for the intended user. In our case, we have specified .
Alternately, you could use port 5902. The 2 in this case would be the display number for janevnc (remember the message displayed when janevnc ran the command).
Click the Add button and the mapping will be added under Forwarded ports. This is where we are adding port forwarding for the SSH session; when the user connects to localhost at port 5900, the connection will be automatically tunnelled through SSH to the remote server’s port 5905.
Go back to the Sessions items and save the session for janevnc. Click the Open button and a new terminal session will open for janevnc. Log in as janevnc with the appropriate UNIX password:
Next start VNC Viewer again. This time, in the VNC Server address, type <^> and let VNC server choose the encryption method:
Click the Connect button.
You will still get the dialogue box warning you about an unencrypted session, but this time you can safely ignore it. VNC Viewer doesn’t know about the port it’s being forwarded to (this was set in the SSH session just started) and assumes you are trying to connect to the local machine.
Accepting this warning will show the familiar password prompt. Enter janevnc’s VNC password to access the remote desktop.
So how do you know the session was encrypted? If you think about it, we had set port forwarding in the SSH session. If an SSH session wasn’t established, port forwarding wouldn’t have worked. In fact, if you close the terminal window and log out of the PuTTY session then try to connect with VNC Viewer alone, a connection attempt to would show the following error message:
So, if the connection works, you can be confident that the connection is encrypted.
Remember that you will want to establish the SSH connection first every time you use VNC, to make sure your connection is always encrypted.
Accessing your CentOS Linux system from a GUI front end can make system administration much simpler. You can connect from any client operating system and don’t have to depend on web-based hosting control panels. VNC has a much smaller footprint compared to most control panels.
Although we have shown how two ordinary users can connect with their VNC clients, that’s hardly practical in serious production environments. In reality, users will have customized applications or browsers for accessing the server. Running a number of VNC services for each user also creates an unnecessary burden on system resources, not to mention the inherent risks associated with it.
If you decide to install and run VNC on your production Linux server, we strongly recommend using it for administrative purposes only.
Comparison of SSH clients
Further information: Secure Shell
An SSH client is a software program which uses the secure shell protocol to connect to a remote computer. This article compares a selection of notable clients.
The operating systems or virtual machines the SSH clients are designed to run on without emulation include several possibilities:
- Partial indicates that while it works, the client lacks important functionality compared to versions for other OSs but may still be under development.
The list is not exhaustive, but rather reflects the most common platforms today.
- ^ abcOnly for jailbroken devices.
- ^lsh supports only one BSD platform officially, FreeBSD.
- ^Included and enabled by default since windows 10 version 1803. Win32-OpenSSH can be installed as an optional component in the Windows versiones before Windows 10 version 1803 to Windows 10 version 1709. Portable version can be download from Win32-OpenSSH for other versions.
- ^The majority of Linux distributions have OpenSSH as an official package, but a few do not.
|SSH2||Additional protocols||Port forwarding and Tunneling||Session|
|Kerberos||IPv6||Terminal||SFTP/SCP||Proxy client[Note 2]|
|Yes||Yes||Yes||No||Yes||Yes||No||Yes||Yes||Yes||Yes||Yes||SOCKS 4, 5; HTTP|
|Bitvise SSH Client||GUI or command line||No||Yes||No||No||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||SOCKS 4, 5|
|OpenSSH (OpenBSD Secure Shell)||command line||No[Note 5]||Yes||No||No||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||ProxyCommand|
|PuTTY||GUI or command line||Yes||Yes||Yes||Yes||Yes||Yes||No||Yes||Yes[Note 6]||Yes||Yes||Yes[Note 7]||SOCKS 4, 5; HTTP; Telnet; Local|
|SecureCRT||GUI||Yes||Yes||Yes||Yes||Yes||Yes||No||Yes||Yes||Yes||Yes||Yes||SOCKS 4, 5; HTTP; Telnet; Generic|
|No||Yes||Yes||No||No||No||No||No||Yes||Yes||Yes||Yes||SOCKS 4, 5; HTTP|
|Tera Term||GUI||Yes||Yes||Yes||No||Yes||No||No||No||No||Yes||Yes||SCP||SOCKS 4, 5; HTTP; Telnet|
|TN3270 Plus||GUI||Yes||Yes||Yes||No||No||Yes||No||Yes||No||Yes||Yes||No||SOCKS 4|
|TtyEmulator||GUI or command line||Yes||Yes||Yes||Yes||Yes||Yes||No||Yes||No||No||Yes||No||SOCKS 4,4a, 5; HTTP Local|
|WinSCP[Note 8]||GUI or command line||Yes||Yes||No||No||limited[Note 9]||No||No||No||Yes||Yes||simple||Yes||SOCKS 4, 5; HTTP; Telnet; Local|
|ZOC||TDI or command line||Yes||Yes||Yes||Yes||Yes||Yes||No||No||Yes||Yes||Yes||SCP and SFTP through terminal[Note 10]||SOCKS 4; 5; HTTP; Jumpserver|
|Kerberos||IPv6||Terminal||SFTP/SCP||Proxy client[Note 2]|
- ^The ability to transmit mouse input to text mode applications such as Midnight Commander
- ^Only when the terminal itself supports mouse input. Most graphical ones do, e.g. xterm.
- ^No native URL highlighting; however most graphical consoles support URL highlighting.
- ^Validated when running OpenSSH 2.1 on Red Hat Enterprise Linux 6.2 in FIPS mode or when running OpenSSH 1.1 on Red Hat Enterprise Linux 5 in FIPS mode
- ^OpenSSH supports the minimal certificate format since v5.4. "OpenSSH Release Notes: 5.4". OpenBSD Project. 2010-03-08. Retrieved 2021-08-30.
- ^PuTTY does not support tabs directly, but many wrappers are available that do (e.g. PuTTY Connection Manager, SuperPuTTY, MTPuTTY, PuTTYTabManager, mRemoteNG, WinSSHTerm, PuTTY Manager, PuttyTabs and TWSC (Terminal Window ShortCuts)).
- ^PuTTY does not support hyperlinks, but some forks of PuTTY do (e.g. PuTTY Tray and KiTTY).
- ^PuTTY does not support smart cards, but is supported in puttywincrypt, PuTTY-CAC, and in Smartcard Authentication – Secure & Easy putty version.
- ^Putty v71.0 does not support OpenSSH certificates. See Ben Harris' 2016-04-21 wish.  and 
Authentication key algorithms
This table lists standard authentication key algorithms implemented by SSH clients. Some SSH implementations include both server and client implementations and support custom non-standard authentication algorithms not listed in this table.
|Name||ssh-dss[AuthNote 1]||ssh-rsa||RSA with SHA-2||ECDSA with SHA-2||Security keys|
|Bitvise SSH Client||?||?||?||?||?||?||?||?|
|OpenSSH (OpenBSD Secure Shell)||Yes[AuthNote 2]||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes||Yes|
|RSA with SHA-2||ECDSA with SHA-2||Security keys|
- ^ is based on Digital Signature Algorithm which is sensitive to entropy, secrecy, and uniqueness of its random signature value.
- ^By default, disabled at run-time since OpenSSH 7.0 released in 2015.
Add the line exclude = barman* to the bottom of all blocks in /etc/yum.repos.d/pgdg-redhat-all.repo
name=PostgreSQL common RPMs for RHEL/CentOS $releasever – $basearch
yum makecache fast command is executed again.
BARMAN is installed with yum install -y barman command.
PostgreSQL 12 database is installed.
PostgreSQL 12 database is initialized.
PostgreSQL 12 database service is enabled + started and its status is checked.
/etc/barman/barman.conf -> Global configuration file. It contains general backup configurations such as log file, backup user, backup directory.
The original version of barman.conf is backed up.
After being backed up, the following parameter values are updated.
In the conf file, directories that are specified to be backup (barman_home = / backup / barman) are created and their authorities are given.
TRANSACTIONS TO BE TAKEN ON THE DATABASE SERVER WHICH WE WANT TO BACKUP
In order for our PostgreSQL database to accept incoming connections, listen_addresses = ‘*’ must be in the postgresql.conf file in /var/lib/pgsql/12/data/ directory by default.
The file path may differ depending on the version and the installed directory.
Sample output is as follows.
If the listen_addresses value is not *, it must be set and the postgresql service must be restarted for the changes to take effect.
We create the barman user with superuser right for backup operations and streaming_barman user with replication right for streaming operations.
In order for the BARMAN server to connect to the database and take backups, we add the following lines, which contain the BARMAN server’s IP to the pg_hba.conf file.
Note: In the default installation of PostgreSQL 12 version, pg_hba.conf file is located in >>> /var/lib/pgsql/12/data/pg_hba.conf directory.
PostgreSQL service needs reload operation for a change made in pg_hba.conf file to take effect. By connecting with psql, we can do it with the following command.
Access rules to the database can be controlled as follows.
THE FOLLOWING PROCESSES WILL BE PERFORMED ON WHICH SERVER, I WRITE IN THE TITLE SECTION.
We can check the access of the barman user we created with the following command.
BARMAN BACKUP SERVER >>> POSTGRESQL DB
For streaming operations, we can check the connection of the streaming_barman user which has replication rights as follows.
BARMAN BACKUP SERVER >>> POSTGRESQL DB
In order for barman and streaming_barman users to connect to the database from which we will take backup from the barman server without the need to enter a password, the following operations are done.
In the .pgpass file, we enter the IP of the database to be backed up, the barman user/password and the streaming_barman user/password.
TO BE MADE IN BARMAN BACKUP SERVER
With the barman user, a connection test is made to the database server from which we will take a backup from the BARMAN server without the need to enter a password.
BARMAN BACKUP SERVER >>> POSTGRESQL DB
With the streaming_barman user, a connection test is made to the database server from which we will take a backup from the BARMAN server without the need to enter a password.
BARMAN BACKUP SERVER >>> POSTGRESQL DB
SSH-KEY is created by passing to the barman user on the BARMAN server
SSH-KEY is created by passing to the postgres user on the database server that we will take a backup.
Passing to postgres user on the database server that we will take a backup
Created .ssh / authorized_keys file
The following key which we have created with the barman user on the BARMAN server, is pasted into an application like notepad++ and made into a single line
SINGLE-LINE KEY IS ENTERED IN THE .ssh/authorized_keys FILE OF USER OF postgres ON THE DATABASE SERVER
SSH test is made to PostgreSQL database server from which we will take a backup from BARMAN server.
THE POSTGRESQL DATABASE AUTHORIZED OPERATING SYSTEM USER (POSTGRES) PASSWORD MUST BE READY.
We create a configuration file for the server that we want to backup in the /etc/barman.d/ directory of the BARMAN server.
Ownership of the configuration file created for the server that we will take a backup on the BARMAN server is changed to be the barman.
We check if the server that we added to the BARMAN server to backup is listed / not listed.
The status of the server we have added to the BARMAN server to back up is controlled by the command barman check server_name
SYNTAX: barman check [server_name]
Replication slot: FAILED (replication slot ‘barman’ doesn’t exist. Please execute ‘barman receive-wal –create-slot dwh’). To resolve the error, the following command is run and a slot with the name of the barman is created on the PostgreSQL Database (DWH) that we want to backup.
To verify WAL archiving process, run the following command.
After the above processes, the final situation is as below.
WAL archive: FAILED and recieve-wal running FAILED errors are gone.
THE ERROR IS EXISTING AT THE SSH CONNECTION.
The following commands are run on the database server attempting to SSH to fix the connection error.
After the above operations, the error is gone in the barman check [server_name] command.
Minimum redundancy requirements: FAILED (have 0 backups, expected at least 1) error can be ignored. Because we haven’t taken any backup yet.
We take our first backup with the barman backup [server_name] –wait command.
After backup, barman check [server_name] output is as below.
The backups we received are listed with the barman list-backup [server_name] command .
The status of the server we have backed up is checked with barman status [server_name] command.