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How To List and Delete iptables Firewall Rules
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======
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![How To List and Delete iptables Firewall Rules][1]
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We'll show you, how to list and delete iptables firewall rules. Iptables is a command line utility that allows system administrators to configure the packet filtering rule set on Linux. iptables requires elevated privileges to operate and must be executed by user root, otherwise it fails to function.
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### How to List iptables Firewall Rules
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Iptables allows you to list all the rules which are already added to the packet filtering rule set. In order to be able to check this you need to have SSH access to the server. [Connect to your Linux VPS via SSH][2] and run the following command:
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```
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sudo iptables -nvL
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```
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To run the command above your user need to have `sudo` privileges. Otherwise, you need to [add sudo user on your Linux VPS][3] or use the root user.
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If there are no rules added to the packet filtering ruleset the output should be similar to the one below:
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```
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Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
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pkts bytes target prot opt in out source destination
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Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
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pkts bytes target prot opt in out source destination
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Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
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pkts bytes target prot opt in out source destination
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```
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Since NAT (Network Address Translation) can also be configured via iptables, you can use iptables to list the NAT rules:
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```
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sudo iptables -t nat -n -L -v
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```
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The output will be similar to the one below if there are no rules added:
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```
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Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
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pkts bytes target prot opt in out source destination
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Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
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pkts bytes target prot opt in out source destination
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Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
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pkts bytes target prot opt in out source destination
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```
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If this is the case we recommend you to check our tutorial on How to [Set Up a Firewall with iptables on Ubuntu and CentOS][4] to make your server more secure.
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### How to Delete iptables Firewall Rules
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At some point, you may need to remove a specific iptables firewall rule on your server. For that purpose you need to use the following syntax:
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```
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iptables [-t table] -D chain rulenum
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```
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For example, if you have a firewall rule to block all connections from 111.111.111.111 to your server on port 22 and you want to remove that rule, you can use the following command:
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```
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sudo iptables -D INPUT -s 111.111.111.111 -p tcp --dport 22 -j DROP
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```
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Now that you removed the iptables firewall rule you need to save the changes to make them persistent.
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In case you are using [Ubuntu VPS][5] you need to install additional package for that purpose. To install the required package use the following command:
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```
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sudo apt-get install iptables-persistent
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```
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On **Ubutnu 14.04** you can save and reload the firewall rules using the commands below:
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```
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sudo /etc/init.d/iptables-persistent save
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sudo /etc/init.d/iptables-persistent reload
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```
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On **Ubuntu 16.04** use the following commands instead:
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```
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sudo netfilter-persistent save
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sudo netfilter-persistent reload
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```
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If you are using [CentOS VPS][6] you can save the changes using the command below:
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```
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service iptables save
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```
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Of course, you don't have to list and delete iptables firewall rules if you use one of our [Managed VPS Hosting][7] services, in which case you can simply ask our expert Linux admins to help you list and delete iptables firewall rules on your server. They are available 24×7 and will take care of your request immediately.
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**PS**. If you liked this post, on how to list and delete iptables firewall rules, please share it with your friends on the social networks using the buttons on the left or simply leave a reply below. Thanks.
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--------------------------------------------------------------------------------
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via: https://www.rosehosting.com/blog/how-to-list-and-delete-iptables-firewall-rules/
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作者：[RoseHosting][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://www.rosehosting.com
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[1]:https://www.rosehosting.com/blog/wp-content/uploads/2018/01/How-To-List-and-Delete-iptables-Firewall-Rules.jpg
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[2]:https://www.rosehosting.com/blog/connect-to-your-linux-vps-via-ssh/
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[3]:https://www.rosehosting.com/blog/how-to-create-a-sudo-user-on-ubuntu/
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[4]:https://www.rosehosting.com/blog/how-to-set-up-a-firewall-with-iptables-on-ubuntu-and-centos/
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[5]:https://www.rosehosting.com/ubuntu-vps.html
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[6]:https://www.rosehosting.com/centos-vps.html
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[7]:https://www.rosehosting.com/managed-vps-hosting.html
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@ -1,131 +0,0 @@
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Error establishing a database connection
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======
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![Error establishing a database connection][1]
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Error establishing a database connection, is a very common error when you try to access your WordPress site. The database stores all the important information for your website, including your posts, comments, site configuration, user accounts, theme and plugin settings and so on. If the connection to your database cannot be established, your WordPress website will not load, and more then likely will give you the error: “Error establishing a database connection” In this tutorial we will show you, how to fix Error establishing a database connection in WordPress.
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The most common cause for “Error establishing a database connection” issue, is one of the following:
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Your database has been corrupted
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Incorrect login credentials in your WordPress configuration file (wp-config.php)
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Your MySQL service stopped working due to insufficient memory on the server (due to heavy traffic), or server problems
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![Error establishing a database connection][2]
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### 1. Requirements
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In order to troubleshoot “Error establishing a database connection” issue, a few requirements must be met:
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* SSH access to your server
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* The database is located on the same server
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* You need to know your database username, user password, and name of the database
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Also before you try to fix “Error establishing a database connection” error, it is highly recommended that you make a backup of both your website and database.
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### 1. Corrupted database
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The first step to do when trying to troubleshoot “Error establishing a database connection” problem is to check whether this error is present for both the front-end and the back-end of the your site. You can access your back-end via <http://www.yourdomain.com/wp-admin> (replace “yourdomain” with your actual domain name)
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If the error remains the same for both your front-end and back-end then you should move to the next step.
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If you are able to access the back-end via <https://www.yourdomain.com/wp-admin, > and you see the following message:
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```
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“One or more database tables are unavailable. The database may need to be repaired”
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```
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it means that your database has been corrupted and you need to try to repair it.
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To do this, you must first enable the repair option in your wp-config.php file, located inside the WordPress site root directory, by adding the following line:
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```
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define('WP_ALLOW_REPAIR', true);
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```
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Now you can navigate to this this page: <https://www.yourdomain.com/wp-admin/maint/repair.php> and click the “Repair and Optimize Database button.”
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For security reasons, remember to turn off the repair option be deleting the line we added before in the wp-config.php file.
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If this does not fix the problem or the database cannot be repaired you will probably need to restore it from a backup if you have one available.
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### 2. Check your wp-config.php file
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Another, probably most common reason, for failed database connection is because of incorrect database information set in your WordPress configuration file.
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The configuration file resides in your WordPress site root directory and it is called wp-config.php .
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Open the file and locate the following lines:
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```
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define('DB_NAME', 'database_name');
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define('DB_USER', 'database_username');
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define('DB_PASSWORD', 'database_password');
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define('DB_HOST', 'localhost');
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```
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Make sure the correct database name, username, and password are set. Database host should be set to “localhost”.
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If you ever change your database username and password you should always update this file as well.
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If everything is set up properly and you are still getting the “Error establishing a database connection” error then the problem is probably on the server side and you should move on to the next step of this tutorial.
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### 3. Check your server
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Depending on the resources available, during high traffic hours, your server might not be able to handle all the load and it may stop your MySQL server.
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You can either contact your hosting provider about this or you can check it yourself if the MySQL server is properly running.
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To check the status of MySQL, log in to your server via [SSH][3] and use the following command:
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```
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systemctl status mysql
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```
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Or you can check if it is up in your active processes with:
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```
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ps aux | grep mysql
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```
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If your MySQL is not running you can start it with the following commands:
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```
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systemctl start mysql
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```
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You may also need to check the memory usage on your server.
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To check how much RAM you have available you can use the following command:
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```
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free -m
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```
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If your server is running low on memory you may want to consider upgrading your server.
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### 4. Conclusion
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Most of the time. the “Error establishing a database connection” error can be fixed by following one of the steps above.
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![How to Fix the Error Establishing a Database Connection in WordPress][4]Of course, you don’t have to fix, Error establishing a database connection, if you use one of our [WordPress VPS Hosting Services][5], in which case you can simply ask our expert Linux admins to help you fix the Error establishing a database connection in WordPress, for you. They are available 24×7 and will take care of your request immediately.
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**PS**. If you liked this post, on how to fix the Error establishing a database connection in WordPress, please share it with your friends on the social networks using the buttons on the left or simply leave a reply below. Thanks.
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--------------------------------------------------------------------------------
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via: https://www.rosehosting.com/blog/error-establishing-a-database-connection/
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作者：[RoseHosting][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://www.rosehosting.com
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[1]:https://www.rosehosting.com/blog/wp-content/uploads/2018/02/error-establishing-a-database-connection.jpg
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[2]:https://www.rosehosting.com/blog/wp-content/uploads/2018/02/Error-establishing-a-database-connection-e1517474875180.png
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[3]:https://www.rosehosting.com/blog/connect-to-your-linux-vps-via-ssh/
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[4]:https://www.rosehosting.com/blog/wp-content/uploads/2018/02/How-to-Fix-the-Error-Establishing-a-Database-Connection-in-WordPress.jpg
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[5]:https://www.rosehosting.com/wordpress-hosting.html
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@ -1,118 +0,0 @@
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How to Create a Sudo User on CentOS 7
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======
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![How to create a sudo user on CentOS 7][1]
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We’ll guide you, how to create a sudo user on CentOS 7. Sudo is a Linux command line program that allows you to execute commands as superuser or another system user. The configuration file offers detailed access permissions, including enabling commands only from the invoking terminal; requiring a password per user or group; requiring re-entry of a password every time or never requiring a password at all for a particular command line. It can also be configured to permit passing arguments or multiple commands. In this tutorial we will show you how to create a sudo user on CentOS 7.
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### Steps to Create a New Sudo User on CentOS 7
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#### 1. Connect via SSH
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First of all, [connect to your server via SSH][2]. Once you are logged in, you need to add a new system user.
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#### 2. Add New User in CentOS
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You can add a new system user using the following command:
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```
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# adduser newuser
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```
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You need to replace `newuser` with the name of the user you want to add. Also, you need to set up a password for the newly added user.
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#### 3. Create a Strong Password
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To set up a password you can use the following command:
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```
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# passwd newuser
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```
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Make sure you are using a [strong password][3], otherwise the password will fail against the dictionary check. You will be asked to enter the password again and once you enter it you will be notified that the authentication tokens are updated successfully:
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```
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# passwd newuser
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Changing password for user newuser.
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New password:
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Retype new password:
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passwd: all authentication tokens updated successfully.
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```
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#### 4. Add User to the Wheel Group in CentOS
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The wheel group is a special user group that allows all members in the group to run all commands. Therefore, you need to add the new user to this group so it can run commands as superuser. You can do that by using the following command:
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```
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# usermod -aG wheel newuser
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```
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Again, make sure you are using the name of the actual user instead of `newuser`.
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Now, use `visudo` to open and edit the `/etc/sudoers` file. Make sure that the line that starts with `%wheel` is not commented. It should look exactly like this:
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```
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### Allows people in group wheel to run all commands
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%wheel ALL=(ALL) ALL
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```
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Now that your new user is set up you can switch to that user and test if everything is OK.
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#### 5. Switch to the sudo User
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To switch to the new user, run the following command:
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```
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# su - newuser
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```
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Now run a command that usually doesn’t work for regular users like the one below:
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```
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$ ls -la /root/
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```
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You will get the following error message:
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```
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ls: cannot open directory /root/: Permission denied
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```
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Try to run the same command, now with using `sudo`
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```
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$ sudo ls -ls /root/
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```
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You will need to enter the password for the new user to proceed. If everything is OK, the command will list all the content in the `/root` directory. Another way to test this is to run the following command:
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```
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$ sudo whoami
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```
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The output of the command should be similar to the one below:
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```
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$ sudo whoami
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root
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```
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Congratulations, now you have a sudo user which you can use to manage your CentOS 7, operating system.
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Of course, you don’t have to create a sudo user on CentOS 7, if you use one of our [CentOS 7 Hosting][4] services, in which case you can simply ask our expert Linux admins to create a sudo user on CentOS 7, for you. They are available 24×7 and will take care of your request immediately.
|
||||
|
||||
**PS**. If you liked this post on **how to create a sudo user on CentOS 7** , please share it with your friends on the social networks using the buttons on the left or simply leave a reply below. Thanks.
|
||||
|
||||
--------------------------------------------------------------------------------
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||||
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||||
via: https://www.rosehosting.com/blog/how-to-create-a-sudo-user-on-centos-7/
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||||
|
||||
作者：[RoseHosting][a]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:https://www.rosehosting.com
|
||||
[1]:https://www.rosehosting.com/blog/wp-content/uploads/2018/02/How-to-create-a-sudo-user-on-CentOS-7.jpg
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[2]:https://www.rosehosting.com/blog/connect-to-your-linux-vps-via-ssh/
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||||
[3]:https://www.rosehosting.com/blog/generate-password-linux-command-line/
|
||||
[4]:https://www.rosehosting.com/centos-vps.html
|
||||
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