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      How To Manage Multiple Servers with Ansible Ad Hoc Commands


      Introduction

      Ansible is a modern configuration management tool that facilitates the task of setting up and maintaining remote servers. With a minimalist design intended to get users up and running quickly, it allows you to control one to hundreds of systems from a central location with either playbooks or ad hoc commands.

      Unlike playbooks — which consist of collections of tasks that can be reused — ad hoc commands are tasks that you don’t perform frequently, such as restarting a service or retrieving information about the remote systems that Ansible manages.

      In this cheat sheet guide, you’ll learn how to use Ansible ad hoc commands to perform common tasks such as installing packages, copying files, and restarting services on one or more remote servers, from an Ansible control node.

      Prerequisites

      In order to follow this guide, you’ll need:

      • One Ansible control node. This guide assumes your control node is an Ubuntu 20.04 machine with Ansible installed and configured to connect to your Ansible hosts using SSH keys. Make sure the control node has a regular user with sudo permissions and a firewall enabled, as explained in our Initial Server Setup guide. To set up Ansible, please follow our guide on How to Install and Configure Ansible on Ubuntu 20.04.
      • Two or more Ansible hosts. An Ansible host is any machine that your Ansible control node is configured to automate. This guide assumes your Ansible hosts are remote Ubuntu 20.04 servers. Make sure each Ansible host has:
        • The Ansible control node’s SSH public key added to the authorized_keys of a system user. This user can be either root or a regular user with sudo privileges. To set this up, you can follow Step 2 of How to Set Up SSH Keys on Ubuntu 20.04.
      • An inventory file set up on the Ansible control node. Make sure you have a working inventory file containing all your Ansible hosts. To set this up, please refer to the guide on How To Set Up Ansible Inventories. Then, make sure you’re able to connect to your nodes by running the connection test outlined in the section Testing Connection to Ansible Hosts.

      Testing Connection to Ansible Hosts

      The following command will test connectivity between your Ansible control node and all your Ansible hosts. This command uses the current system user and its corresponding SSH key as the remote login, and includes the -m option, which tells Ansible to run the ping module. It also features the -i flag, which tells Ansible to ping the hosts listed in the specified inventory file

      • ansible all -i inventory -m ping

      If this is the first time you’re connecting to these servers via SSH, you’ll be asked to confirm the authenticity of the hosts you’re connecting to via Ansible. When prompted, type yes and then hit ENTER to confirm.

      You should get output similar to this:

      Output

      server1 | SUCCESS => { "changed": false, "ping": "pong" } server2 | SUCCESS => { "changed": false, "ping": "pong" }

      Once you get a "pong" reply back from a host, it means the connection is live and you’re ready to run Ansible commands on that server.

      Adjusting Connection Options

      By default, Ansible tries to connect to the nodes as a remote user with the same name as your current system user, using its corresponding SSH keypair.

      To connect as a different remote user, append the command with the -u flag and the name of the intended user:

      • ansible all -i inventory -m ping -u sammy

      If you’re using a custom SSH key to connect to the remote servers, you can provide it at execution time with the --private-key option:

      • ansible all -i inventory -m ping --private-key=~/.ssh/custom_id

      Note: For more information on how to connect to nodes, please refer to our How to Use Ansible guide, which demonstrates more connection options.

      Once you’re able to connect using the appropriate options, you can adjust your inventory file to automatically set your remote user and private key, in case they are different from the default values assigned by Ansible. Then, you won’t need to provide those parameters in the command line.

      The following example inventory file sets up the ansible_user variable only for the server1 server:

      ~/ansible/inventory

      server1 ansible_host=203.0.113.111 ansible_user=sammy
      server2 ansible_host=203.0.113.112
      

      Ansible will now use sammy as the default remote user when connecting to the server1 server.

      To set up a custom SSH key, include the ansible_ssh_private_key_file variable as follows:

      ~/ansible/inventory

      server1 ansible_host=203.0.113.111 ansible_ssh_private_key_file=/home/sammy/.ssh/custom_id
      server2 ansible_host=203.0.113.112
      

      In both cases, we have set up custom values only for server1. If you want to use the same settings for multiple servers, you can use a child group for that:

      ~/ansible/inventory

      [group_a]
      203.0.113.111
      203.0.113.112
      
      [group_b]
      203.0.113.113
      
      
      [group_a:vars]
      ansible_user=sammy
      ansible_ssh_private_key_file=/home/sammy/.ssh/custom_id
      

      This example configuration will assign a custom user and SSH key only for connecting to the servers listed in group_a.

      Defining Targets for Command Execution

      When running ad hoc commands with Ansible, you can target individual hosts, as well as any combination of groups, hosts and subgroups. For instance, this is how you would check connectivity for every host in a group named servers:

      • ansible servers -i inventory -m ping

      You can also specify multiple hosts and groups by separating them with colons:

      • ansible server1:server2:dbservers -i inventory -m ping

      To include an exception in a pattern, use an exclamation mark, prefixed by the escape character , as follows. This command will run on all servers from group1, except server2:

      • ansible group1:!server2 -i inventory -m ping

      In case you’d like to run a command only on servers that are part of both group1 and group2, for instance, you should use & instead. Don’t forget to prefix it with a escape character:

      • ansible group1:&group2 -i inventory -m ping

      For more information on how to use patterns when defining targets for command execution, please refer to Step 5 of our guide on How to Set Up Ansible Inventories.

      Running Ansible Modules

      Ansible modules are pieces of code that can be invoked from playbooks and also from the command-line to facilitate executing procedures on remote nodes. Examples include the apt module, used to manage system packages on Ubuntu, and the user module, used to manage system users. The ping command used throughout this guide is also a module, typically used to test connection from the control node to the hosts.

      Ansible ships with an extensive collection of built-in modules, some of which require the installation of additional software in order to provide full functionality. You can also create your own custom modules using your language of choice.

      To execute a module with arguments, include the -a flag followed by the appropriate options in double quotes, like this:

      ansible target -i inventory -m module -a "module options"
      

      As an example, this will use the apt module to install the package tree on server1:

      • ansible server1 -i inventory -m apt -a "name=tree"

      Running Bash Commands

      When a module is not provided via the -m option, the command module is used by default to execute the specified command on the remote server(s).

      This allows you to execute virtually any command that you could normally execute via an SSH terminal, as long as the connecting user has sufficient permissions and there aren’t any interactive prompts.

      This example executes the uptime command on all servers from the specified inventory:

      • ansible all -i inventory -a "uptime"

      Output

      server1 | CHANGED | rc=0 >> 14:12:18 up 55 days, 2:15, 1 user, load average: 0.03, 0.01, 0.00 server2 | CHANGED | rc=0 >> 14:12:19 up 10 days, 6:38, 1 user, load average: 0.01, 0.02, 0.00

      Using Privilege Escalation to Run Commands with sudo

      If the command or module you want to execute on remote hosts requires extended system privileges or a different system user, you’ll need to use Ansible’s privilege escalation module, become. This module is an abstraction for sudo as well as other privilege escalation software supported by Ansible on different operating systems.

      For instance, if you wanted to run a tail command to output the latest log messages from Nginx’s error log on a server named server1 from inventory, you would need to include the --become option as follows:

      • ansible server1 -i inventory -a "tail /var/log/nginx/error.log" --become

      This would be the equivalent of running a sudo tail /var/log/nginx/error.log command on the remote host, using the current local system user or the remote user set up within your inventory file.

      Privilege escalation systems such as sudo often require that you confirm your credentials by prompting you to provide your user’s password. That would cause Ansible to fail a command or playbook execution. You can then use the --ask-become-pass or -K option to make Ansible prompt you for that sudo password:

      • ansible server1 -i inventory -a "tail /var/log/nginx/error.log" --become -K

      Installing and Removing Packages

      The following example uses the apt module to install the nginx package on all nodes from the provided inventory file:

      • ansible all -i inventory -m apt -a "name=nginx" --become -K

      To remove a package, include the state argument and set it to absent:.

      • ansible all -i inventory -m apt -a "name=nginx state=absent" --become -K

      Copying Files

      With the file module, you can copy files between the control node and the managed nodes, in either direction. The following command copies a local text file to all remote hosts in the specified inventory file:

      • ansible all -i inventory -m copy -a "src=./file.txt dest=~/myfile.txt"

      To copy a file from the remote server to your control node, include the remote_src option:

      • ansible all -i inventory -m copy -a "src=~/myfile.txt remote_src=yes dest=./file.txt"

      Changing File Permissions

      To modify permissions on files and directories on your remote nodes, you can use the file module.

      The following command will adjust permissions on a file named file.txt located at /var/www on the remote host. It will set the file’s umask to 600, which will enable read and write permissions only for the current file owner. Additionally, it will set the ownership of that file to a user and a group called sammy:

      • ansible all -i inventory -m file -a "dest=/var/www/file.txt mode=600 owner=sammy group=sammy" --become -K

      Because the file is located in a directory typically owned by root, we might need sudo permissions to modify its properties. That’s why we include the --become and -K options. These will use Ansible’s privilege escalation system to run the command with extended privileges, and it will prompt you to provide the sudo password for the remote user.

      Restarting Services

      You can use the service module to manage services running on the remote nodes managed by Ansible. This will require extended system privileges, so make sure your remote user has sudo permissions and you include the --become option to use Ansible’s privilege escalation system. Using -K will prompt you to provide the sudo password for the connecting user.

      To restart the nginx service on all hosts in group called webservers, for instance, you would run:

      • ansible webservers -i inventory -m service -a "name=nginx state=restarted" --become -K

      Restarting Servers

      Although Ansible doesn’t have a dedicated module to restart servers, you can issue a bash command that calls the /sbin/reboot command on the remote host.

      Restarting the server will require extended system privileges, so make sure your remote user has sudo permissions and you include the --become option to use Ansible’s privilege escalation system. Using -K will prompt you to provide the sudo password for the connecting user.

      Warning: The following command will fully restart the server(s) targeted by Ansible. That might cause temporary disruption to any applications that rely on those servers.

      To restart all servers in a webservers group, for instance, you would run:

      • ansible webservers -i inventory -a "/sbin/reboot" --become -K

      Gathering Information About Remote Nodes

      The setup module returns detailed information about the remote systems managed by Ansible, also known as system facts.

      To obtain the system facts for server1, run:

      • ansible server1 -i inventory -m setup

      This will print a large amount of JSON data containing details about the remote server environment. To print only the most relevant information, include the "gather_subset=min" argument as follows:

      • ansible server1 -i inventory -m setup -a "gather_subset=min"

      To print only specific items of the JSON, you can use the filter argument. This will accept a wildcard pattern used to match strings, similar to fnmatch. For example, to obtain information about both the ipv4 and ipv6 network interfaces, you can use *ipv* as filter:

      • ansible server1 -i inventory -m setup -a "filter=*ipv*"

      Output

      server1 | SUCCESS => { "ansible_facts": { "ansible_all_ipv4_addresses": [ "203.0.113.111", "10.0.0.1" ], "ansible_all_ipv6_addresses": [ "fe80::a4f5:16ff:fe75:e758" ], "ansible_default_ipv4": { "address": "203.0.113.111", "alias": "eth0", "broadcast": "203.0.113.111", "gateway": "203.0.113.1", "interface": "eth0", "macaddress": "a6:f5:16:75:e7:58", "mtu": 1500, "netmask": "255.255.240.0", "network": "203.0.113.0", "type": "ether" }, "ansible_default_ipv6": {} }, "changed": false }

      If you’d like to check disk usage, you can run a Bash command calling the df utility, as follows:

      • ansible all -i inventory -a "df -h"

      Output

      server1 | CHANGED | rc=0 >> Filesystem Size Used Avail Use% Mounted on udev 3.9G 0 3.9G 0% /dev tmpfs 798M 624K 798M 1% /run /dev/vda1 155G 2.3G 153G 2% / tmpfs 3.9G 0 3.9G 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/vda15 105M 3.6M 101M 4% /boot/efi tmpfs 798M 0 798M 0% /run/user/0 server2 | CHANGED | rc=0 >> Filesystem Size Used Avail Use% Mounted on udev 2.0G 0 2.0G 0% /dev tmpfs 395M 608K 394M 1% /run /dev/vda1 78G 2.2G 76G 3% / tmpfs 2.0G 0 2.0G 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup /dev/vda15 105M 3.6M 101M 4% /boot/efi tmpfs 395M 0 395M 0% /run/user/0

      Conclusion

      In this guide, we demonstrated how to use Ansible ad hoc commands to manage remote servers, including how to execute common tasks such as restarting a service or copying a file from the control node to the remote servers managed by Ansible. We’ve also seen how to gather information from the remote nodes using limiting and filtering parameters.

      As an additional resource, you can check Ansible’s official documentation on ad hoc commands.



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      Apache Configuration Error AH00558: Could not reliably determine the server’s fully qualified domain name



      Part of the Series:
      Common Apache Errors

      This tutorial series explains how to troubleshoot and fix some of the most common errors that you may encounter when using the Apache web server.

      Each tutorial in this series includes descriptions of common Apache configuration, network, filesystem, or permission errors. The series begins with an overview of the commands and log files that you can use to troubleshoot Apache. Subsequent tutorials examine specific errors in detail.

      Introduction

      An Apache AH00558: Could not reliably determine the server's fully qualified domain name message is generated when Apache is not configured with a global ServerName directive. The message is mainly for informational purposes, and an AH00558 error will not prevent Apache from running correctly.

      In this tutorial you will learn how to detect an AH00558 message using the methods described in the How to Troubleshoot Common Apache Errors tutorial at the beginning of this series. You will also learn how to set a ServerName directive to resolve the message.

      If you have already determined that your Apache server is affected by an AH00558 message and you would like to skip the troubleshooting steps, the Setting a Global ServerName Directive step at the end of this tutorial explains how to resolve the message.

      Troubleshooting Using systemctl

      The first step when you are troubleshooting an AH00558: Could not reliably determine the server's fully qualified domain name message is to check Apache’s status using systemctl. The output from systemctl will in many cases contain all the information that you need to resolve the message.

      On Ubuntu and Debian-derived Linux distributions, run the following to check Apache’s status:

      Ubuntu and Debian Systems

      • sudo systemctl status apache2.service -l --no-pager

      On CentOS Fedora, and RedHat-derived systems, use this command to examine Apache’s status:

      CentOS and Fedora Systems

      • sudo systemctl status httpd.service -l --no-pager

      The -l flag will ensure that systemctl outputs the entire contents of a line, instead of substituting in ellipses () for long lines. The --no-pager flag will output the entire log to your screen without invoking a tool like less that only shows a screen of content at a time.

      You should receive output that is similar to the following:

      Output

      ● apache2.service - The Apache HTTP Server Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled) Drop-In: /lib/systemd/system/apache2.service.d └─apache2-systemd.conf Active: active (running) since Wed 2020-07-29 14:30:03 UTC; 33min ago Process: 34 ExecStart=/usr/sbin/apachectl start (code=exited, status=0/SUCCESS) Main PID: 46 (apache2) Tasks: 55 (limit: 2344) CGroup: /system.slice/apache2.service ├─46 /usr/sbin/apache2 -k start ├─47 /usr/sbin/apache2 -k start └─48 /usr/sbin/apache2 -k start Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Starting The Apache HTTP Server... Jul 29 14:30:03 68e2cf19f3f1 apachectl[34]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Started The Apache HTTP Server.

      The highlighted line that contains the AH00558 message is the important one. Essentially, it informs you that Apache couldn’t find a valid ServerName directive in its configuration file, so it will use the first IP address it detects. In this example, it’s the server’s public IP address: 172.17.02. If you are troubleshooting an AH00558 message, the IP address that is detected may be different, or it may be a human readable DNS name.

      If your systemctl output contains an auto-detected value of any IP address or hostname, skip to the last section of this tutorial, Setting a Global ServerName Directive to resolve the issue. In that section you will configure Apache with a safe default ServerName value using the IP address for localhost: 127.0.0.1.

      If your systemctl output does not indicate a value that you can use for the ServerName directive, the next section of this tutorial explains how to examine the systemd logs using journalctl to locate an AH00558 message.

      Troubleshooting Using journalctl

      To examine the systemd logs for Apache you will use the journalctl command. When invoking journalctl, there are two specific flags that will help you locate specific messages if there is a large volume of log entries.

      The first flag that you will add to the journalctl invocation is the --since today flag. It will limit the output of the command to log entries beginning at 00:00:00 of the current day only. Using this option will help restrict the volume of log entries that you need to examine when checking for errors.

      The second flag that you will use is the same --no-pager option that you used with systemctl, which will output the entire log to your screen at once.

      On Ubuntu and Debian-derived systems, run the following command:

      • sudo journalctl -u apache2.service --since today --no-pager

      On CentOS, Fedora, and RedHat-derived systems, use this command to inspect the logs:

      • sudo journalctl -u httpd.service --since today --no-pager

      If your Apache server is generating an AH00558 message, look through the journalctl command output for lines like the following:

      Output

      -- Logs begin at Wed 2020-07-29 14:30:02 UTC, end at Wed 2020-07-29 14:45:03 UTC. -- . . . Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Starting The Apache HTTP Server... Jul 29 14:30:03 68e2cf19f3f1 apachectl[34]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Started The Apache HTTP Server.

      The second line of output is the AH00558 message. The line includes the server’s public IP address, which is the address that Apache automatically detects and sets as a default at runtime. With this message as confirmation of an AH00558 error, you can proceed to the Setting a Global ServerName Directive to resolve the issue.

      Otherwise, the next section explains how to diagnose an AH00558 error message using the apachectl command.

      Troubleshooting using apachectl

      An AH00558: Could not reliably determine the server's fully qualified domain name error can be detected using Apache’s apachectl utility. With apachectl you can catch messages like these before reloading or restarting Apache, and you can avoid having to search through systemctl and journalctl logs to locate errors.

      To check your Apache configuration for an AH00558 message, run the following command:

      • sudo apachectl configtest

      You should receive output like the following if your server is affected by an AH00558 error message:

      Output

      AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message Syntax OK

      As with the previous sections in this tutorial that used systemctl and journalctl to locate AH00558 messages, the line that contains the AH00558 message, highlighted in the previous example, is the important one. Again note that the IP address 172.17.0.2 in this example may be different on your server.

      The next section of this tutorial explains how to set the ServerName directive to resolve AH00558 error messages.

      Setting a Global ServerName Directive

      To resolve an AH00558: Could not reliably determine the server's fully qualified domain name error message, you will need to add a ServerName directive to your Apache configuration. Apache uses the ServerName directive to map incoming HTTP requests to an IP address or DNS hostname using VirtualHost directives in order to handle requests for multiple sites using a single server.

      The error message notes that a global ServerName directive should also be set. Doing so will ensure that Apache can gracefully handle incoming requests that do not map to a VirtualHost without generating additional errors.

      For maximum compatibility with various Apache configurations, use the value of 127.0.0.1 for your global ServerName directive. You can use a different IP address or DNS name that corresponds to your server’s configuration if you need to, but it is safest to use 127.0.0.1.

      On Ubuntu and Debian-derived systems, open the /etc/apache2/apache2.conf file with root privileges using nano or your preferred text editor:

      • sudo nano /etc/apache2/apache2.conf

      Add a line containing ServerName 127.0.0.1 to the end of the file:

      /etc/apache2/apache2.conf

      . . .
      # Include the virtual host configurations:
      IncludeOptional sites-enabled/*.conf
      
      # vim: syntax=apache ts=4 sw=4 sts=4 sr noet
      ServerName 127.0.0.1
      

      On CentOS, Fedora, and RedHat-derived systems, open the /etc/httpd/conf/httpd.conf file with root privileges using nano or your preferred text editor:

      • sudo nano /etc/httpd/conf/httpd.conf

      Add the ServerName 127.0.0.1 line to the end of the file:

      /etc/httpd/conf/httpd.conf

      . . .
      # Supplemental configuration
      #
      # Load config files in the "/etc/httpd/conf.d" directory, if any.
      IncludeOptional conf.d/*.conf
      ServerName 127.0.0.1
      

      Save and close the file when you are finished. If you used nano, do so by pressing CTRL + X, Y, and then ENTER.

      Once you have added the ServerName directive to your configuration, run apachectl to test that the configuration is valid.

      • sudo apachectl configtest

      A successful apachectl configtest invocation should result in output like this:

      Output

      Syntax OK

      You can now restart Apache using the appropriate systemctl restart command for your Linux distribution.

      On Ubuntu and Debian-derived systems, run the following:

      • sudo systemctl restart apache2.service

      On CentOS, Fedora, and RedHat-derived systems use this command to restart Apache:

      • sudo systemctl restart httpd.service

      After you restart Apache, the AH00558 error message will no longer appear in your logs. You can confirm the messages are silenced by running any of the three systemctl, journalctl, or apachectl commands that are demonstrated in this tutorial.

      Conclusion

      In this tutorial you learned about AH00558: Could not reliably determine the server's fully qualified domain name error messages. While these messages do not prevent Apache from running, they can be resolved by setting a global ServerName directive.

      You learned how to search for AH00558 error messages using the systemctl, journalctl, and apachectl commands. Finally, you learned how to edit your Apache configuration on various Linux distributions to silence the messages.

      If you would like to learn more about how Apache uses ServerName directives, the Apache documentation about Name-Based Virtual Hosts explains the directive in more detail.



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      How To Install and Configure Zabbix to Securely Monitor Remote Servers on Ubuntu 20.04


      Not using Ubuntu 20.04?


      Choose a different version or distribution.

      The author selected the Computer History Museum to receive a donation as part of the Write for DOnations program.

      Introduction

      Zabbix is open-source monitoring software for networks and applications. It offers real-time monitoring of thousands of metrics collected from servers, virtual machines, network devices, and web applications. These metrics can help you determine the current health of your IT infrastructure and detect problems with hardware or software components before customers complain. Useful information is stored in a database so you can analyze data over time and improve the quality of provided services or plan upgrades of your equipment.

      Zabbix uses several options for collecting metrics, including agentless monitoring of user services and client-server architecture. To collect server metrics, it uses a small agent on the monitored client to gather data and send it to the Zabbix server. Zabbix supports encrypted communication between the server and connected clients, so your data is protected while it travels over insecure networks.

      The Zabbix server stores its data in a relational database powered by MySQL or PostgreSQL. You can also store historical data in NoSQL databases like Elasticsearch and TimescaleDB. Zabbix provides a web interface so you can view data and configure system settings.

      In this tutorial, you will configure Zabbix on two Ubuntu 20.04 machines. One will be configured as the Zabbix server, and the other as a client that you’ll monitor. The Zabbix server will use a MySQL database to record monitoring data and use Nginx to serve the web interface.

      Prerequisites

      To follow this tutorial, you will need:

      • Two Ubuntu 20.04 servers set up by following the Initial Server Setup Guide for Ubuntu 20.04, including a non-root user with sudo privileges and a firewall configured with ufw. On one server, you will install Zabbix; this tutorial will refer to this as the Zabbix server. It will monitor your second server; this second server will be referred to as the second Ubuntu server.

      • The server that will run the Zabbix server needs Nginx, MySQL, and PHP installed. Follow Steps 1–3 of our Ubuntu 20.04 LEMP Stack guide to configure those on your Zabbix server.

      • A registered domain name. This tutorial will use your_domain throughout. You can purchase a domain name from Namecheap, get one for free with Freenom, or use the domain registrar of your choice.

      • Both of the following DNS records set up for your Zabbix server. If you are using DigitalOcean, please see our DNS documentation for details on how to add them.

        • An A record with your_domain pointing to your Zabbix server’s public IP address.
        • An A record with www.your_domain pointing to your Zabbix server’s public IP address.

      Additionally, because the Zabbix Server is used to access valuable information about your infrastructure that you would not want unauthorized users to access, it’s important that you keep your server secure by installing a TLS/SSL certificate. This is optional but strongly encouraged. If you would like to secure your server, follow the Let’s Encrypt on Ubuntu 20.04 guide after Step 3 of this tutorial.

      Step 1 — Installing the Zabbix Server

      First, you need to install Zabbix on the server where you installed MySQL, Nginx, and PHP. Log in to this machine as your non-root user:

      • ssh sammy@zabbix_server_ip_address

      Zabbix is available in Ubuntu’s package manager, but it’s outdated, so use the official Zabbix repository to install the latest stable version. Download and install the repository configuration package:

      • wget https://repo.zabbix.com/zabbix/5.0/ubuntu/pool/main/z/zabbix-release/zabbix-release_5.0-1+focal_all.deb
      • sudo dpkg -i zabbix-release_5.0-1+focal_all.deb

      You will see the following output:

      Output

      Selecting previously unselected package zabbix-release. (Reading database ... 64058 files and directories currently installed.) Preparing to unpack zabbix-release_5.0-1+focal_all.deb ... Unpacking zabbix-release (1:5.0-1+focal) ... Setting up zabbix-release (1:5.0-1+focal) ...

      Update the package index so the new repository is included:

      Then install the Zabbix server and web frontend with MySQL database support:

      • sudo apt install zabbix-server-mysql zabbix-frontend-php

      Also, install the Zabbix agent, which will let you collect data about the Zabbix server status itself.

      • sudo apt install zabbix-agent

      Before you can use Zabbix, you have to set up a database to hold the data that the Zabbix server will collect from its agents. You can do this in the next step.

      Step 2 — Configuring the MySQL Database for Zabbix

      You need to create a new MySQL database and populate it with some basic information in order to make it suitable for Zabbix. You’ll also create a specific user for this database so Zabbix isn’t logging in to MySQL with the root account.

      Log in to MySQL as the root user:

      Create the Zabbix database with UTF-8 character support:

      • create database zabbix character set utf8 collate utf8_bin;

      Then create a user that the Zabbix server will use, give it access to the new database, and set the password for the user:

      • create user zabbix@localhost identified by 'your_zabbix_mysql_password';
      • grant all privileges on zabbix.* to zabbix@localhost;

      That takes care of the user and the database. Exit out of the database console.

      Next you have to import the initial schema and data. The Zabbix installation provided you with a file that sets this up.

      Run the following command to set up the schema and import the data into the zabbix database. Use zcat since the data in the file is compressed:

      • zcat /usr/share/doc/zabbix-server-mysql*/create.sql.gz | mysql -uzabbix -p zabbix

      Enter the password for the zabbix MySQL user that you configured when prompted.

      This command may take a minute or two to execute. If you see the error ERROR 1045 (28000): Access denied for userzabbix@'localhost' (using password: YES) then make sure you used the right password for the zabbix user.

      In order for the Zabbix server to use this database, you need to set the database password in the Zabbix server configuration file. Open the configuration file in your preferred text editor. This tutorial will use nano:

      • sudo nano /etc/zabbix/zabbix_server.conf

      Look for the following section of the file:

      /etc/zabbix/zabbix_server.conf

      ...
      ### Option: DBPassword                           
      #       Database password. Ignored for SQLite.   
      #       Comment this line if no password is used.
      #                                                
      # Mandatory: no                                  
      # Default:                                       
      # DBPassword=
      ...
      

      These comments in the file explain how to connect to the database. You need to set the DBPassword value in the file to the password for your database user. Add this line after those comments to configure the database:

      /etc/zabbix/zabbix_server.conf

      ...
      DBPassword=your_zabbix_mysql_password
      ...
      

      Save and close zabbix_server.conf by pressing CTRL+X, followed by Y and then ENTER if you’re using nano.

      You’ve now configured the Zabbix server to connect to the database. Next, you will configure the Nginx web server to serve the Zabbix frontend.

      Step 3 — Configuring Nginx for Zabbix

      To configure Nginx automatically, install the automatic configuration package:

      • sudo apt install zabbix-nginx-conf

      As a result, you will get the configuration file /etc/zabbix/nginx.conf, as well as a link to it in the Nginx configuration directory /etc/nginx/conf.d/zabbix.conf.

      Next, you need to make changes to this file. Open the configuration file:

      • sudo nano /etc/zabbix/nginx.conf

      The file contains an automatically generated Nginx server block configuration. It contains two lines that determine the server name and what port it is listening on:

      /etc/zabbix/nginx.conf

      server {
      #        listen          80;
      #        server_name     example.com;
      ...
      

      Uncomment the two lines, and replace example.com with your domain name. Your settings will look like this:

      /etc/zabbix/nginx.conf

      server {
              listen          80;
              server_name     your_domain;
      ...
      

      Save and close the file. Next, test to make sure that there are no syntax errors in any of your Nginx files and reload the configuration:

      • sudo nginx -t
      • sudo nginx -s reload

      Now that Nginx is set up to serve the Zabbix frontend, you will make some modifications to your PHP setup in order for the Zabbix web interface to work properly.

      Note: As mentioned in the Prerequisites section, it is recommended that you enable SSL/TLS on your server. If you would like to do this, follow our Ubuntu 20.04 Let’s Encrypt tutorial before you move on to Step 4 to obtain a free SSL certificate for Nginx. This process will automatically detect your Zabbix server block and configure it for HTTPS. After obtaining your SSL/TLS certificates, you can come back and complete this tutorial.

      Step 4 — Configuring PHP for Zabbix

      The Zabbix web interface is written in PHP and requires some special PHP server settings. The Zabbix installation process created a PHP-FPM configuration file that contains these settings. It is located in the directory /etc/zabbix and is loaded automatically by PHP-FPM. You need to make a small change to this file, so open it up with the following:

      • sudo nano /etc/zabbix/php-fpm.conf

      The file contains PHP settings that meet the necessary requirements for the Zabbix web interface. However, the timezone setting is commented out by default. To make sure that Zabbix uses the correct time, you need to set the appropriate timezone:

      /etc/zabbix/php-fpm.conf

      ...
      php_value[max_execution_time] = 300
      php_value[memory_limit] = 128M
      php_value[post_max_size] = 16M
      php_value[upload_max_filesize] = 2M
      php_value[max_input_time] = 300
      php_value[max_input_vars] = 10000
      ; php_value[date.timezone] = Europe/Riga
      

      Uncomment the timezone line highlighted in the preceding code block and change it to your timezone. You can use this list of supported time zones to find the right one for you. Then save and close the file.

      Now restart PHP-FPM to apply these new settings:

      • sudo systemctl restart php7.4-fpm.service

      You can now start the Zabbix server:

      • sudo systemctl start zabbix-server

      Then check whether the Zabbix server is running properly:

      • sudo systemctl status zabbix-server

      You will see the following status:

      Output

      ● zabbix-server.service - Zabbix Server Loaded: loaded (/lib/systemd/system/zabbix-server.service; disabled; vendor preset: enabled) Active: active (running) since Fri 2020-06-12 05:59:32 UTC; 36s ago Process: 27026 ExecStart=/usr/sbin/zabbix_server -c $CONFFILE (code=exited, status=0/SUCCESS) ...

      Finally, enable the server to start at boot time:

      • sudo systemctl enable zabbix-server

      The server is set up and connected to the database. Next, set up the web frontend.

      Step 5 — Configuring Settings for the Zabbix Web Interface

      The web interface lets you see reports and add hosts that you want to monitor, but it needs some initial setup before you can use it. Launch your browser and go to the address http://zabbix_server_name or https://zabbix_server_name if you set up Let’s Encrypt. On the first screen, you will see a welcome message. Click Next step to continue.

      On the next screen, you will see the table that lists all of the prerequisites to run Zabbix.

      Prerequisites

      All of the values in this table must be OK, so verify that they are. Be sure to scroll down and look at all of the prerequisites. Once you’ve verified that everything is ready to go, click Next step to proceed.

      The next screen asks for database connection information.

      DB Connection

      You told the Zabbix server about your database, but the Zabbix web interface also needs access to the database to manage hosts and read data. Therefore enter the MySQL credentials you configured in Step 2. Click Next step to proceed.

      On the next screen, you can leave the options at their default values.

      Zabbix Server Details

      The Name is optional; it is used in the web interface to distinguish one server from another in case you have several monitoring servers. Click Next step to proceed.

      The next screen will show the pre-installation summary so you can confirm everything is correct.

      Summary

      Click Next step to proceed to the final screen.

      The web interface setup is now complete. This process creates the configuration file /usr/share/zabbix/conf/zabbix.conf.php, which you could back up and use in the future. Click Finish to proceed to the login screen. The default user is Admin and the password is zabbix.

      Before you log in, set up the Zabbix agent on your second Ubuntu server.

      Step 6 — Installing and Configuring the Zabbix Agent

      Now you need to configure the agent software that will send monitoring data to the Zabbix server.

      Log in to the second Ubuntu server:

      • ssh sammy@second_ubuntu_server_ip_address

      Just like on the Zabbix server, run the following commands to install the repository configuration package:

      • wget https://repo.zabbix.com/zabbix/5.0/ubuntu/pool/main/z/zabbix-release/zabbix-release_5.0-1+focal_all.deb
      • sudo dpkg -i zabbix-release_5.0-1+focal_all.deb

      Next, update the package index:

      Then install the Zabbix agent:

      • sudo apt install zabbix-agent

      While Zabbix supports certificate-based encryption, setting up a certificate authority is beyond the scope of this tutorial. But you can use pre-shared keys (PSK) to secure the connection between the server and agent.

      First, generate a PSK:

      • sudo sh -c "openssl rand -hex 32 > /etc/zabbix/zabbix_agentd.psk"

      Show the key by using cat so you can copy it somewhere:

      • cat /etc/zabbix/zabbix_agentd.psk

      The key will look something like this:

      Output

      75ad6cb5e17d244ac8c00c96a1b074d0550b8e7b15d0ab3cde60cd79af280fca

      Save this for later; you will need it to configure the host.

      Now edit the Zabbix agent settings to set up its secure connection to the Zabbix server. Open the agent configuration file in your text editor:

      • sudo nano /etc/zabbix/zabbix_agentd.conf

      Each setting within this file is documented via informative comments throughout the file, but you only need to edit some of them.

      First you have to edit the IP address of the Zabbix server. Find the following section:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: Server
      #       List of comma delimited IP addresses, optionally in CIDR notation, or DNS names of Zabbix servers and Zabbix proxies.
      #       Incoming connections will be accepted only from the hosts listed here.
      #       If IPv6 support is enabled then '127.0.0.1', '::127.0.0.1', '::ffff:127.0.0.1' are treated equally
      #       and '::/0' will allow any IPv4 or IPv6 address.
      #       '0.0.0.0/0' can be used to allow any IPv4 address.
      #       Example: Server=127.0.0.1,192.168.1.0/24,::1,2001:db8::/32,zabbix.example.com
      #
      # Mandatory: yes, if StartAgents is not explicitly set to 0
      # Default:
      # Server=
      
      Server=127.0.0.1
      ...
      

      Change the default value to the IP of your Zabbix server:

      /etc/zabbix/zabbix_agentd.conf

      ...
      Server=zabbix_server_ip_address
      ...
      

      By default, Zabbix server connects to the agent. But for some checks (for example, monitoring the logs), a reverse connection is required. For correct operation, you need to specify the Zabbix server address and a unique host name.

      Find the section that configures the active checks and change the default values:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ##### Active checks related
      
      ### Option: ServerActive
      #       List of comma delimited IP:port (or DNS name:port) pairs of Zabbix servers and Zabbix proxies for active checks.
      #       If port is not specified, default port is used.
      #       IPv6 addresses must be enclosed in square brackets if port for that host is specified.
      #       If port is not specified, square brackets for IPv6 addresses are optional.
      #       If this parameter is not specified, active checks are disabled.
      #       Example: ServerActive=127.0.0.1:20051,zabbix.domain,[::1]:30051,::1,[12fc::1]
      #
      # Mandatory: no
      # Default:
      # ServerActive=
      
      ServerActive=zabbix_server_ip_address
      
      ### Option: Hostname
      #       Unique, case sensitive hostname.
      #       Required for active checks and must match hostname as configured on the server.
      #       Value is acquired from HostnameItem if undefined.
      #
      # Mandatory: no
      # Default:
      # Hostname=
      
      Hostname=Second Ubuntu Server
      ...
      

      Next, find the section that configures the secure connection to the Zabbix server and enable pre-shared key support. Find the TLSConnect section, which looks like this:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSConnect
      #       How the agent should connect to server or proxy. Used for active checks.
      #       Only one value can be specified:
      #               unencrypted - connect without encryption
      #               psk         - connect using TLS and a pre-shared key
      #               cert        - connect using TLS and a certificate
      #
      # Mandatory: yes, if TLS certificate or PSK parameters are defined (even for 'unencrypted' connection)
      # Default:
      # TLSConnect=unencrypted
      ...
      

      Then add this line to configure pre-shared key support:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSConnect=psk
      ...
      

      Next, locate the TLSAccept section, which looks like this:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSAccept
      #       What incoming connections to accept.
      #       Multiple values can be specified, separated by comma:
      #               unencrypted - accept connections without encryption
      #               psk         - accept connections secured with TLS and a pre-shared key
      #               cert        - accept connections secured with TLS and a certificate
      #
      # Mandatory: yes, if TLS certificate or PSK parameters are defined (even for 'unencrypted' connection)
      # Default:
      # TLSAccept=unencrypted
      ...
      

      Configure incoming connections to support pre-shared keys by adding this line:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSAccept=psk
      ...
      

      Next, find the TLSPSKIdentity section, which looks like this:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSPSKIdentity
      #       Unique, case sensitive string used to identify the pre-shared key.
      #
      # Mandatory: no
      # Default:
      # TLSPSKIdentity=
      ...
      

      Choose a unique name to identify your pre-shared key by adding this line:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSPSKIdentity=PSK 001
      ...
      

      You’ll use this as the PSK ID when you add your host through the Zabbix web interface.

      Then set the option that points to your previously created pre-shared key. Locate the TLSPSKFile option:

      /etc/zabbix/zabbix_agentd.conf

      ...
      ### Option: TLSPSKFile
      #       Full pathname of a file containing the pre-shared key.
      #
      # Mandatory: no
      # Default:
      # TLSPSKFile=
      ...
      

      Add this line to point the Zabbix agent to your PSK file you created:

      /etc/zabbix/zabbix_agentd.conf

      ...
      TLSPSKFile=/etc/zabbix/zabbix_agentd.psk
      ...
      

      Save and close the file. Now you can restart the Zabbix agent and set it to start at boot time:

      • sudo systemctl restart zabbix-agent
      • sudo systemctl enable zabbix-agent

      For good measure, check that the Zabbix agent is running properly:

      • sudo systemctl status zabbix-agent

      You will see the following status, indicating the agent is running:

      Output

      ● zabbix-agent.service - Zabbix Agent Loaded: loaded (/lib/systemd/system/zabbix-agent.service; enabled; vendor preset: enabled) Active: active (running) since Fri 2020-06-12 08:19:54 UTC; 25s ago ...

      The agent will listen on port 10050 for connections from the server. Configure UFW to allow connections to this port:

      You can learn more about UFW in How To Set Up a Firewall with UFW on Ubuntu 20.04.

      Your agent is now ready to send data to the Zabbix server. But in order to use it, you have to link to it from the server’s web console. In the next step, you will complete the configuration.

      Step 7 — Adding the New Host to the Zabbix Server

      Installing an agent on a server you want to monitor is only half of the process. Each host you want to monitor needs to be registered on the Zabbix server, which you can do through the web interface.

      Log in to the Zabbix Server web interface by navigating to the address http://zabbix_server_name or https://zabbix_server_name:

      The Zabbix login screen

      When you have logged in, click on Configuration and then Hosts in the left navigation bar. Then click the Create host button in the top right corner of the screen. This will open the host configuration page.

      Creating a host

      Adjust the Host name and IP address to reflect the host name and IP address of your second Ubuntu server, then add the host to a group. You can select an existing group, for example Linux servers, or create your own group. The host can be in multiple groups. To do this, enter the name of an existing or new group in the Groups field and select the desired value from the proposed list.

      Before adding the group, click the Templates tab.

      Adding a template to the host

      Type Template OS Linux by Zabbix agent in the Search field and then select it from the list to add this template to the host.

      Next, navigate to the Encryption tab. Select PSK for both Connections to host and Connections from host. Then set PSK identity to PSK 001, which is the value of the TLSPSKIdentity setting of the Zabbix agent you configured previously. Then set PSK value to the key you generated for the Zabbix agent. It’s the one stored in the file /etc/zabbix/zabbix_agentd.psk on the agent machine.

      Setting up the encryption

      Finally, click the Add button at the bottom of the form to create the host.

      You will see your new host in the list. Wait for a minute and reload the page to see green labels indicating that everything is working fine and the connection is encrypted.

      Zabbix shows your new host

      If you have additional servers you need to monitor, log in to each host, install the Zabbix agent, generate a PSK, configure the agent, and add the host to the web interface following the same steps you followed to add your first host.

      The Zabbix server is now monitoring your second Ubuntu server. Now, set up email notifications to be notified about problems.

      Step 8 — Configuring Email Notifications

      Zabbix automatically supports many types of notifications: email, OTRS, Slack, Telegram, SMS, etc. You can see the full list of integrations at the Zabbix website.

      As an example, this tutorial will configure notifications for the Email media type.

      Click on Administration, and then Media types in the left navigation bar. You will see the list of all media types. There are two preconfigured options for emails: for the plain text notification and for the HTML notifications. In this tutorial you will use plain text notification. Click on Email.

      Adjust the SMTP options according to the settings provided by your email service. This tutorial uses Gmail’s SMTP capabilities to set up email notifications; if you would like more information about setting this up, see How To Use Google’s SMTP Server.


      Note: If you use 2-Step Verification with Gmail, you need to generate an App Password for Zabbix. You’ll only have to enter an App password once during setup. You will find instructions on how to generate this password in the Google Help Center.

      If you are using Gmail, type in smtp.gmail.com for the SMTP server field, 465 for the SMTP server port field, gmail.com for SMTP helo, and your email for SMTP email. Then choose SSL/TLS for Connection security and Username and password for Authentication. Enter your Gmail address as the Username, and the App Password you generated from your Google account as the Password.

      Setting up email media type

      On the Message templates tab you can see the list of predefined messages for various types of notifications. Finally, click the Update button at the bottom of the form to update the email parameters.

      Now you can test sending notifications. To do this, click the Test underlined link in the corresponding line.

      You will see a pop-up window. Enter your email address in the Send to field and click the Test button. You will see a message about the successful sending and you will receive a test message.

      Testing email

      Close the pop-up by clicking the Cancel button.

      Now, create a new user. Click on Administration, and then Users in the left navigation bar. You will see the list of users. Then click the Create user button in the top right corner of the screen. This will open the user configuration page:

      Creating a user

      Enter the new username in the Alias field and set up a new password. Next, add the user to the administrator’s group. Type Zabbix administrators in the Groups field and select it from the proposed list.

      Once you’ve added the group, click the Media tab and click on the Add underlined link (not the Add button below it). You will see a pop-up window.

      Adding an email

      Select the Email option from the Type drop down. Enter your email address in the Send to field. You can leave the rest of the options at the default values. Click the Add button at the bottom to submit.

      Now navigate to the Permissions tab. Select Zabbix Super Admin from the User type drop-down menu.

      Finally, click the Add button at the bottom of the form to create the user.

      Note: Using the default password is not safe. In order to change the password of the built-in user Admin click on the alias in the list of users. Then click Change password, enter a new password, and confirm the changes by clicking Update button.

      Now you need to enable notifications. Click on the Configuration tab and then Actions in the left navigation bar. You will see a pre-configured action, which is responsible for sending notifications to all Zabbix administrators. You can review and change the settings by clicking on its name. For the purposes of this tutorial, use the default parameters. To enable the action, click on the red Disabled link in the Status column.

      Now you are ready to receive alerts. In the next step, you will generate one to test your notification setup.

      Step 9 — Generating a Test Alert

      In this step, you will generate a test alert to ensure everything is connected. By default, Zabbix keeps track of the amount of free disk space on your server. It automatically detects all disk mounts and adds the corresponding checks. This discovery is executed every hour, so you need to wait a while for the notification to be triggered.

      Create a temporary file that’s large enough to trigger Zabbix’s file system usage alert. To do this, log in to your second Ubuntu server if you’re not already connected:

      • ssh sammy@second_ubuntu_server_ip_address

      Next, determine how much free space you have on the server. You can use the df command to find out:

      The command df will report the disk space usage of your file system, and the -h will make the output human-readable. You’ll see output like the following:

      Output

      Filesystem Size Used Avail Use% Mounted on /dev/vda1 78G 1.4G 77G 2% /

      In this case, the free space is 77G. Your free space may differ.

      Use the fallocate command, which allows you to pre-allocate or de-allocate space to a file, to create a file that takes up more than 80% of the available disk space. This will be enough to trigger the alert:

      • fallocate -l 70G /tmp/temp.img

      After around an hour, Zabbix will trigger an alert about the amount of free disk space and will run the action you configured, sending the notification message. You can check your inbox for the message from the Zabbix server. You will see a message like:

      Problem started at 09:49:08 on 2020.06.12
      Problem name: /: Disk space is low (used > 80%)
      Host: Second Ubuntu Server
      Severity: Warning
      Operational data: Space used: 71.34 GB of 77.36 GB (92.23 %)
      Original problem ID: 106
      

      You can also navigate to the Monitoring tab and then Dashboard to see the notification and its details.

      Main dashboard

      Now that you know the alerts are working, delete the temporary file you created so you can reclaim your disk space:

      After a minute Zabbix will send the recovery message and the alert will disappear from the main dashboard.

      Conclusion

      In this tutorial, you learned how to set up a simple and secure monitoring solution that will help you monitor the state of your servers. It can now warn you of problems, and you have the opportunity to analyze the processes occurring in your IT infrastructure.

      To learn more about setting up monitoring infrastructure, check out our Monitoring topic page.



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