How to Check for Installed Packages on CentOS

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While managing your server, you’ll sometimes need to check on which software (or packages) you have installed on your system. You’ll need to know package names, version numbers, dates of installation, etc. In this Liquid Web tutorial, we’re going to be discussing how to inspect packages installed on your CentOS system. There are several ways to accomplish this, and we’ll discuss a few of them. Let’s dig in! To use these commands, you’ll need to log in to your server via SSH. For more information, see Logging into Your Server via Secure Shell (SSH).

Using RPM Package Manager

This first command uses the rpm package manager to poll for installed packages. This command allows you to see every installed package on your system, along with the version that is currently installed:

rpm -qa
Note the -q means “query” and -a means “all”. We’re asking rpm to query all installed packages.

Let’s examine a small portion of the results in detail. Note that you might not have these specific packages installed on your CentOS server. The important thing here is to understand how to read the output. Take a look at a small excerpt of entries from the list.kpartx-0.4.9-123.el7.x86_64
dracut-033-554.el7.x86_64
elfutils-libs-0.172-2.el7.x86_64

Each entry can be broken up into three parts. From left to right, these are:
Package name: (kpartx)
Version: (0.4.9-123.el7)
Architecture: (x86_64)

Instead of displaying all installed packages, rpm can also be used to search for a single package. Let’s use rpm to query kpartx:
rpm -q kpartx
You’ll see the output displays the same package name and version we saw from rpm -qa.
kpartx-0.4.9-123.el7.x86_64

Using Yum to Check Installed Packages

Using rpm is not the only way to check for installed packages on your system. Now we will discuss how to use “yum” to accomplish the same task. Try the following command:
yum list installed
You will see that the list yum provides is formatted slightly differently. Let’s look at an entry in depth.
whois.x86_64 5.1.1-2.el7 @base
The first column shows the package name and architecture: (whois.x86_64).
The second column shows the version installed: (5.1.1-2.el7).
Finally the third column shows the repository the software was installed from: (@base).

Using Yum to View Historical Installation Data

We can also use yum to view historical installation data on your system. Run the following command to see a list of anytime yum was used to install, remove, or upgrade a package:
yum history
Here is an example of the output you might see. Your system will show different results here, and that is OK. We’re just interested in learning how to read the output.
ID | Command line | Date and time | Action(s) | Altered
-------------------------------------------------------------------------------
10 | upgrade | 2019-06-01 04:13 | I, U | 12 EE
9 | install whois | 2019-05-04 17:40 | Install | 1
8 | install python36 | 2019-05-03 21:23 | Install | 2
7 | install epel-release | 2019-05-03 21:02 | Install | 1
6 | install bind-utils | 2019-05-03 19:33 | Install | 2
5 | install docker-ce docker | 2019-05-03 17:37 | Install | 4
4 | install yum-utils yum-co | 2019-05-03 17:26 | Install | 6
3 | install git | 2019-05-03 17:19 | Install | 4
2 | install vim | 2019-05-03 17:18 | Install | 31
1 | update | 2019-05-03 17:09 | I, U | 57
history list

Notice the column headings: “ID number, Data and time, Action(s), and Altered.” This is a good summary of when yum was used, but it is lacking detailed information. Let’s examine one of these history entries in detail. Try the following command, replacing “ID_NUMBER” with the actual ID you want to inspect.
yum history info ID_NUMBER

Here is some example output:
Loaded plugins: fastestmirror
Transaction ID : 9
Begin time : Sat May 4 17:40:24 2019
Begin rpmdb : 356:8ab21eca9f4a219812e33c41a73fbd4eb7de1ed8
End time : (0 seconds)
End rpmdb : 357:cf2bf4588ba4d3263d1c9af051c3bcc525596a68
User : Cloud User <centos>
Return-Code : Success
Command Line : install whois
Transaction performed with:
Installed rpm-4.11.3-35.el7.x86_64 installed
Installed yum-3.4.3-161.el7.centos.noarch installed
Installed yum-plugin-fastestmirror-1.1.31-50.el7.noarch installed
Packages Altered:
Install whois-5.1.1-2.el7.x86_64 @base
history info

In this tutorial, we discussed how to use rpm and yum to search your CentOS server for installed packages. These utilities are both critical tools for Linux sysadmins on CentOS systems. Of course if you have any questions about how to use these utilities on your own Liquid Web server, let us know! The Most Helpful Humans in Hosting are standing by 24×7 and we’ll be happy to answer your questions.

How to Set Up A Firewall Using Iptables on Ubuntu 16.04

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This guide will walk you through the steps for setting up a firewall using iptables in Ubuntu 16.04. We’ll show you some common commands for manipulating the firewall, and teach you how to create your own rules.

 

What are Iptables in Ubuntu?

The utility iptables is a Linux based firewall that comes pre-installed on many Linux distributions. It is a leading solution for software-based firewalls. It’s a critical tool for Linux system administrators to learn and understand. Any publicly facing server on the Internet should have some form of firewall enabled for security reasons. In a typical configuration, you would only open ports for the services that you wish to be accessible via the Internet. All other ports would remain closed and inaccessible via the Internet. For example, in a typical server, you may want to open ports for your web services, but you probably would not want to make your database accessible to the public!

 

Pre-flight

Working with iptables requires root privileges on your Linux box. The rest of this guide assumes you have logged in as root. Please exercise caution, as commands issued to iptables take effect immediately. You will be manipulating how your server is accessible to the outside world, so it’s possible to lock yourself out from your own server!

Note
If you’re a Liquid Web customer, check out our VPN + IPMI remote management solutions. These solutions can help you restore access to your server even if you’ve blocked out the outside world. We have a VPN configuration guide to get you started. Of course, our support staff is also standing by 24×7 in the event you get locked out.

 

How Do Iptables Work?

Iptables works by inspecting predefined firewall rules. Incoming server traffic is compared against these rules, and if iptables finds a match, it takes action. If iptables is unable to find a match, it will apply a default policy action. Typical usage is to set iptables to allow matched rules, and deny all others.

 

How Can I See Firewall Rules in Ubuntu?

Before making any changes to your firewall, it is best practice to view the existing rule set and understand what ports are already open or closed. To list all firewall rules, run the following command.

iptables -L

If this is a brand new Ubuntu 16.04 installation, you may see there are no rules defined! Here is an example “empty” output with no rules set:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

If you’re running Ubuntu 16.04 on a Liquid Web VPS, you’ll see we’ve already configured a basic firewall for you. There are usually three essential sections to look at in the iptables ruleset. When dealing with iptables rulesets, they are called “chains”, particularly “Chain INPUT”, “Chain FORWARD”, and “Chain OUTPUT”. The input chain handles traffic coming into your server while the output chain handles the traffic leaving your server. The forwarding chain handles server traffic that is not destined for local delivery. As you can surmise, the traffic is forwarded by our server  to its intended destination.

 

Common Firewall Configurations

The default action is listed in “policy”. If traffic doesn’t match any of the chain rules, iptables will perform this default policy action. You can see that with an empty iptables configuration, the firewall is accepting all connections and not blocking anything! This is not ideal, so let’s change this. Here is an example firewall configuration allowing some common ports, and denying all other traffic.

iptables -A INPUT -i lo -j ACCEPT

iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A INPUT -p icmp -j ACCEPT

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

iptables -A INPUT -p tcp --dport 80 -j ACCEPT

iptables -A INPUT -p tcp --dport 443 -j ACCEPT

iptables -A INPUT -p udp --dport 1194 -j ACCEPT

iptables -A INPUT -s 192.168.0.100 -j ACCEPT

iptables -A INPUT -s 192.168.0.200 -j DROP

iptables -P INPUT DROP

iptables -P FORWARD DROP

iptables -P OUTPUT ACCEPT

We will break down these rules one at a time.

iptables -A INPUT -i lo -j ACCEPT

This first command tells the INPUT chain to accept all traffic on your loopback interface. We specify the loopback interface with -i lo. The -j ACCEPT portion is telling iptables to take this action if traffic matches our rule.


iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

Next, we’ll allow connections that are already established or related. This can be especially helpful for traffic like SSH, where you may initiate an outbound connection and wish to accept incoming traffic of the connection you intentionally established.


iptables -A INPUT -p icmp -j ACCEPT

This command tells your server not to block ICMP (ping) packets. This can be helpful for network troubleshooting and monitoring purposes. Note that the -p icmp portion is telling iptables the protocol for this rule is ICMP.


How Do I Allow a Port in Ubuntu?

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

TCP port 22 is commonly used for SSH. This command allows TCP connections on port 22. Change this if you are running SSH on a different port. Notice since SSH uses TCP, we’ve specified the protocol using -p tcp in this rule.


iptables -A INPUT -p tcp --dport 80 -j ACCEPT

iptables -A INPUT -p tcp --dport 443 -j ACCEPT

These two commands allow web traffic. Regular HTTP uses TCP port 80, and encrypted HTTPS traffic uses TCP port 443.


iptables -A INPUT -p udp --dport 1194 -j ACCEPT

This is a less commonly used port, but here is an example of how to open port 1194 utilizing the UDP protocol instead of TCP. Note that in this example we’ve specified UDP by using -p udp.


How Do I Allow an IP Address in Ubuntu?

iptables -A INPUT -s 192.168.0.100 -j ACCEPT

You can configure iptables to always accept connections from an IP address, regardless of what port the connections arrive on. This is commonly referred to as “whitelisting”, and can be helpful in certain circumstances. We’re whitelisting 192.168.0.100 in this example. Typically you would want to be very restrictive with this action and only allow trusted sources.


How Do I Block an IP Address in Ubuntu?

iptables -A INPUT -s 192.168.0.200 -j DROP

You can also use iptables to block all connections from an IP address or IP range, regardless of what port they arrive on. This can be helpful if you need to block specific known malicious IPs. We’re using 192.168.0.200 as our IP to block in this example.


How Do I Block All Other Ports?

iptables -P INPUT DROP

Next, we tell iptables to block all other inputs. We’re only allowing a few specific ports in our example, but if you had other ports needed, be sure to insert them before issuing the DROP command.


How Do I Forward Traffic in Ubuntu?

iptables -P FORWARD DROP

Likewise, we’re going to drop forwarded packets. Iptables is very powerful, and you can use it to configure your server as a network router. Our example server isn’t acting as a router, so we won’t be using the FORWARD chain.


How Do I Allow All Outbound Traffic?

iptables -P OUTPUT ACCEPT

Finally, we want to allow all outgoing traffic originating from our server. We’re mostly worried about outside traffic hitting our server, and not blocking our own box from accessing the outside world.


How Do I Permanently Save IP Rules?

To make your firewall rules persist after a reboot, we need to save them. The following command will save the current ruleset:

/sbin/iptables-save


How Do I Reset My Iptable?

To wipe out all existing firewall rules and return to a blank slate, you can issue the following command. Remember that an empty iptables configuration allows all traffic to your server, so you typically would not want to leave your server unprotected in this state for very long. Nevertheless, this can be very helpful when configuring new firewall rulesets and you need to revert to a blank slate.

iptables -F

 

We’ve covered a lot of ground in this article! Configuring iptables can seem like a daunting process when first looking at an extensive firewall ruleset, but if you break down the rules one at a time, it becomes much easier to understand the process. When used correctly, iptables is an indispensable tool for hardening your server’s security. Liquid Web customers enjoy our highly trained support staff, standing by 24×7, if you have questions on iptables configurations. Have fun configuring your firewall!

How to Install and Configure Fail2ban on Ubuntu Server 16.04

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Have you ever logged into your server and seen a message such as this?

Last failed login: Fri Dec 28 11:37:02 MST 2018 from 192.168.0.102 on ssh:notty
There were 942 failed login attempts since the last successful login.
Last login: Mon Dec 24 13:35:57 2018 from 192.168.0.101

What happened here? This message is informing me that while I was logged out, there were 942 failed attempts to access my server via SSH! This type of message is a strong indicator that my server was probably under a “brute force” attack. In this type of scenario, an attacker will attempt to randomly guess passwords repeatedly until they get lucky with the correct password. This is one reason why using a secure password is so important! Fear not, Fail2ban can be a fantastic tool for dynamically thwarting these types of brute force attacks. This tutorial will walk you through installing and configuring Fail2ban to help protect sshd from brute force attacks. Let’s dig in!

Note:
The remainder of this tutorial requires you to have root privileges. Start by either logging in as root or prefix these commands with sudo.

 

Installing Fail2ban on Ubuntu Server 16.04 is simple. Run the following two commands to install the program:

apt-get update

apt-get install fail2ban -y

We will start the service, so it is running.

service fail2ban restart

Finally, we check to make sure Fail2ban is running after the restart:

service fail2ban status

The output should display active (running) which indicates the service is up and we’re ready to proceed to configuration.

 

Now that Fail2ban is installed and running, we can define custom rules for what services it protects, and how to handle violations.

First, create a configuration file for Fail2ban. This file doesn’t exist by default, but Fail2ban will look for this file and read the contents if it exists:

touch /etc/fail2ban/jail.local

Now we’ll open the configuration file for editing. We’re using vi as our text editor in this example, but feel free to use nano or whatever text editor you are most comfortable with. (Related: check out our helpful tutorial if you need to brush up on how to use vi.) Run the following command to open the file for editing:

vi /etc/fail2ban/jail.local

Paste in the following contents, and save the file:

[DEFAULT] ignoreip = 127.0.0.1/8 ::1
bantime = 3600
findtime = 600
maxretry = 5
[sshd] enabled = true

Let’s review the options we just set. First, we are telling Fail2ban to ignore IP addresses 127.0.0.1 and ::1. These are the IPv4 and IPv6 addresses for localhost, respectively. For the remaining lines, it is important to understand Fail2ban reads time as seconds in the configuration file. These rules will ban IP addresses for one hour {bantime = 3600}, if they make 5 mistakes {maxretry = 5}, within 10 minutes {findtime = 600}. Finally, we enabled the jail for sshd. Feel free to adjust these numbers to your liking, but please consider the following:

Note:
Setting a ban time of -1 will result in a permanent ban on that IP address. You may need to contact Liquid Web support if you accidentally block yourself from your own server. Consider these options carefully!

Now that we have created a configuration to use, restart Fail2ban so that our new rules are read and utilized:

service fail2ban restart

We will also double check to make sure Fail2ban is running after the restart:

service fail2ban status

Note:
If Fail2ban does not start successfully after creating your configuration file, it is possible you have a typo in the configuration file /etc/fail2ban/jail.local. Check the file contents and try again!

 

At this point, you have successfully installed and configured Fail2ban, congratulations! For the remainder of this tutorial, we will show you how to use to use the program and how to manage IP blocks.

Run the following command to check the status of Fail2ban:

fail2ban-client status

Example output shows you the number of currently configured jails. Right now we have only created a jail for sshd:

Status
|- Number of jail:    1
`- Jail list:    sshd

You can also poll the detailed status of individual jails. This command will check the status of the sshd jail we just configured:

fail2ban-client status sshd

Example output shows no IPs blocked, looks good!

Status for the jail: sshd
|- Filter
|  |- Currently failed:    0
|  |- Total failed:    0
|  `- File list:                 /var/log/auth.log
`- Actions
|- Currently banned:    0
|- Total banned:    0
`- Banned IP list:

Now, for example, I’m going to fail five attempts to SSH to my server. After the fifth failed attempt, my IP should be automatically blocked! The following shows the output from my workstation when I try to SSH to the server after the fifth failed attempt:

ssh root@192.168.0.101
ssh: connect to host 192.168.0.101 port 22: Connection refused

The “connection refused” message indicates that the server’s firewall is now blocking us.

Back on the server, let’s again check the status of the SSH jail by running:

fail2ban-client status sshd

The output shows that my IP has indeed been blocked! Looking at the status, we can see my workstation’s IP address has been added to the “Banned IP list”.

Status for the jail: sshd
|- Filter
|  |- Currently failed:    1
|  |- Total failed:    1
|  `- File list:                 /var/log/auth.log
`- Actions
|- Currently banned:    1
|- Total banned:    1
`- Banned IP list:    192.168.0.102

Finally, we will demonstrate how to remove a banned IP. This is helpful if you have clients that accidentally block themselves from incorrect password attempts. The syntax for this command is as follows:

fail2ban-client set <JAIL NAME> unbanip <IP ADDRESS>

For example, this command will delist 192.168.0.102 from the sshd jail.

fail2ban-client  set sshd unbanip 192.168.0.102

Let’s double check our work and make sure my IP address has been successfully unblocked:

fail2ban-client status sshd

Status for the jail: sshd
|- Filter
|  |- Currently failed:    1
|  |- Total failed:    6
|  `- File list:                 /var/log/auth.log
`- Actions
|- Currently banned:    0
|- Total banned:    1
`- Banned IP list:

That wraps it up for this tutorial! We only discussed protecting sshd in this tutorial, but Fail2ban can be used to help protect all kinds of other services such as httpd. We encourage you to do some further reading and see what it is capable of! Just remember that while Fail2ban is awesome, it is not a replacement for a strong set of firewall rules. When properly configured, however, Fail2ban is a great tool to help further harden your server’s security. Have fun and happy IP blocking!

 

Install Rsync and Lsync on CentOS, Fedora or Red Hat

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Have you ever needed to copy files from your local computer over to your web server? You may have previously used File Transfer Protocol (FTP) applications for this task, but FTP is prone to being insecure and can be challenging to work with over the command line. What if there was a better way? In this tutorial, we’ll be covering two popular utilities in the Linux world to securely assist in file transfers, rsync and lsyncd. We’ll show you how to install and use both in this article. Let’s dig in!

Continue reading “Install Rsync and Lsync on CentOS, Fedora or Red Hat”