“It is an open source continuous monitoring tool which monitors network, applications and servers.”
• It allows you to detect and repair problems and mitigate future issues before they affect end-users and customers
• It is developed for monitoring servers, applications and networks
• It provides a centralized view of your entire IT infrastructure and detailed up-to-date status information
Features of Nagios
Exercise - Installing & Configuring Nagios
Before beginning the work on Nagios you need to install Nagios
Section 1 – Nagios Installation
1. You must have superuser privileges on the Ubuntu 14.04 server that will run Nagios. Ideally, you will be using a non-root user with superuser privileges.
2. A LAMP stack is also required.
3. Install Apache
sudo apt-get update
sudo apt-get install apache2 You can do a spot check right away to verify that everything went as planned by visiting your server's public IP address in your web browser (see the note under the next heading to find out what your public IP address is if you do not have this information already):
http://your_server_IP_address
You will see the default Ubuntu 14.04 Apache web page
4. Install MySQL
sudo apt-get install mysql-server php5-mysql
sudo mysql_install_db
sudo mysql_secure_installation
You will be asked to enter the password you set for the MySQL root account.
5. Install PHP
sudo apt-get install php5 libapache2-mod-php5 php5-mcrypt
sudo nano /etc/apache2/mods-enabled/dir.conf It will look like this:
<IfModule mod_dir.c>
DirectoryIndex index.html index.cgi index.pl index.php index.xhtml index.htm
</IfModule>
We want to move the PHP index file highlighted above to the first position after the DirectoryIndexspecification, like this:
<IfModule mod_dir.c>
DirectoryIndex index.php index.html index.cgi index.pl index.xhtml index.htm
</IfModule>
After this, we need to restart the Apache web server in order for our changes to be recognized. You can do this by typing this:
sudo service apache2 restart
6. Install PHP Modules
sudo apt-get install php5-cli
7. Install Nagios Create Nagios User and Group We must create a user and group that will run the Nagios process. Create a "nagios" user and "nagcmd" group, then add the user to the group with these commands:
sudo useradd nagios
sudo groupadd nagcmd
sudo usermod -a -G nagcmd nagios
Install Build Dependencies
Because we are building Nagios Core from source, we must install a few development libraries that will allow us to complete the build. While we're at it, we will also install apache2-utils, which will be used to set up the Nagios web interface. First, update your apt-get package lists:
sudo apt-get update
Then install the required packages:
sudo apt-get install build-essential libgd2-xpm-dev openssl libssl-dev xinetd apache2-utils unzip
Let's install Nagios now.
Install Nagios Core Download the source code for the latest stable release of Nagios Core. Go to the Nagios downloads page and click the Skip to download link below the form. Copy the link address for the latest stable release so you can download it to your Nagios server.
At the time of this writing, the latest stable release is Nagios 4.1.1. Download it to your home directory with curl:
cd ~
curl -L -O https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.1.1.tar.gz
Extract the Nagios archive with this command:
tar xvf nagios-*.tar.gz
Then change to the extracted directory:
cd nagios-*
Before building Nagios, we must configure it. If you want to configure it to use postfix (which you can install with apt-get), add --with-mail=/usr/sbin/sendmail to the following command:
./configure --with-nagios-group=nagios --with-command-group=nagcmd
Now compile Nagios with this command:
make all
Now we can run these make commands to install Nagios, init scripts, and sample configuration files:
sudo make install
sudo make install-commandmode
sudo make install-init
sudo make install-config
sudo /usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
In order to issue external commands via the web interface to Nagios, we must add the web server user, www-data, to the nagcmd group:
sudo usermod -G nagcmd www-data
Install Nagios Plugins Find the latest release of Nagios Plugins here: Nagios Plugins Download. Copy the link address for the latest version, and copy the link address so you can download it to your Nagios server.
At the time of this writing, the latest version is Nagios Plugins 2.1.1. Download it to your home directory with curl:
cd ~
curl -L -O http://nagios-plugins.org/download/nagios-plugins-2.1.1.tar.gz
Extract Nagios Plugins archive with this command:
tar xvf nagios-plugins-*.tar.gz
Then change to the extracted directory:
cd nagios-plugins-*
Before building Nagios Plugins, we must configure it. Use this command:
./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
Now compile Nagios Plugins with this command:
make
Then install it with this command:
sudo make install
Install NRPE
Find the source code for the latest stable release of NRPE at the NRPE downloads page. Download the latest version to your Nagios server. At the time of this writing, the latest release is 2.15. Download it to your home directory with curl:
cd ~
curl -L -O http://downloads.sourceforge.net/project/nagios/nrpe-2.x/nrpe-2.15/nrpe-2.15.tar.gz
Extract the NRPE archive with this command:
tar xvf nrpe-*.tar.gz
Then change to the extracted directory:
cd nrpe-*
Configure NRPE with these commands:
./configure --enable-command-args --with-nagios-user=nagios --with-nagios-group=nagios --with-ssl=/usr/bin/openssl --with-ssl-lib=/usr/lib/x86_64-linux-gnu
Now build and install NRPE and its xinetd startup script with these commands:
make all
sudo make install
sudo make install-xinetd
sudo make install-daemon-config Open the xinetd startup script in an editor:
sudo vi /etc/xinetd.d/nrpe
Modify the only_from line by adding the private IP address of the your Nagios server to the end (substitute in the actual IP address of your server):
only_from = 127.0.0.1 10.132.224.168
Save and exit. Only the Nagios server will be allowed to communicate with NRPE. Restart the xinetd service to start NRPE:
sudo service xinetd restart
Now that Nagios 4 is installed, we need to configure it. Configure Nagios Now let's perform the initial Nagios configuration. You only need to perform this section once, on your Nagios server. Organize Nagios Configuration Open the main Nagios configuration file in your favorite text editor. We'll use vi to edit the file:
sudo vi /usr/local/nagios/etc/nagios.cfg
Now find an uncomment this line by deleting the #:
#cfg_dir=/usr/local/nagios/etc/servers
Save and exit.
Now create the directory that will store the configuration file for each server that you will monitor:
sudo mkdir /usr/local/nagios/etc/servers
Configure Nagios Contacts Open the Nagios contacts configuration in your favorite text editor. We'll use vi to edit the file:
sudo vi /usr/local/nagios/etc/objects/contacts.cfg
Find the email directive, and replace its value (the highlighted part) with your own email address:
email nagios@localhost ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******
Save and exit.
Configure check_nrpe Command
Let's add a new command to our Nagios configuration:
sudo vi /usr/local/nagios/etc/objects/commands.cfg
Add the following to the end of the file:
define command{
command_name check_nrpe
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}
Save and exit. This allows you to use the check_nrpe command in your Nagios service definitions. Configure Apache Enable the Apache rewrite and cgi modules:
sudo a2enmod rewrite
sudo a2enmod cgi
Use htpasswd to create an admin user, called "nagiosadmin", that can access the Nagios web interface:
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
Enter a password at the prompt. Remember this password, as you will need it to access the Nagios web interface.
Note: If you create a user that is not named "nagiosadmin", you will need to edit /usr/local/nagios/etc/cgi.cfg and change all the "nagiosadmin" references to the user you created. Now create a symbolic link of nagios.conf to the sites-enabled directory:
sudo ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/ Nagios is ready to be started.
Let's do that, and restart Apache:
sudo service nagios start
sudo service apache2 restart
In case Nagios service does not start follow these steps:
sudo vi /etc/systemd/system/nagios.service
and added the following: [Unit] Description=Nagios BindTo=network.target
[Install] WantedBy=multi-user.target [Service] User=nagios Group=nagios Type=simple ExecStart=/usr/local/nagios/bin/nagios /usr/local/nagios/etc/nagios.cfg
Then the following: sudo systemctl enable /etc/systemd/system/nagios.service sudo systemctl start nagios sudo systemctl restart nagios
Accessing the Nagios Web Interface Open your favorite web browser, and go to your Nagios server (substitute the IP address or hostname for the highlighted part):
http://nagios_server_public_ip/nagios
Because we configured Apache to use htpasswd, you must enter the login credentials that you created earlier. We used "nagiosadmin" as the username: After authenticating, you will be see the default Nagios home page. Click on the Hosts link, in the left navigation bar, to see which hosts Nagios is monitoring:
As you can see, Nagios is monitoring only "localhost", or itself. Let's monitor another host with Nagios! Monitor a Host with NRPE In this section, we'll show you how to add a new host to Nagios, so it will be monitored. Repeat this section for each server you wish to monitor. On a server that you want to monitor, update apt-get:
sudo apt-get update
Now install Nagios Plugins and NRPE:
sudo apt-get install nagios-plugins nagios-nrpe-server Configure Allowed Hosts Now, let's update the NRPE configuration file. Open it in your favorite editor (we're using vi):
sudo vi /etc/nagios/nrpe.cfg
... and add Nagios Server IP 192.168.1.9 to the server_address.
server_address=192.168.1.9
Find the allowed_hosts directive, and add the private IP address of your Nagios server to the comma-delimited list (substitute it in place of the highlighted example):
allowed_hosts=127.0.0.1,10.132.224.168
Save and exit. This configures NRPE to accept requests from your Nagios server, via its private IP address. Configure Allowed NRPE Commands Look up the name of your root filesystem (because it is one of the items we want to monitor):
df -h / We will be using the filesystem name in the NRPE configuration to monitor your disk usage (it is probably /dev/vda). Now open nrpe.cfg for editing:
sudo vi /etc/nagios/nrpe.cfg
The NRPE configuration file is very long and full of comments. There are a few lines that you will need to find and modify:
server_address: Set to the private IP address of this host
allowed_hosts: Set to the private IP address of your Nagios server
command[check_hda1]: Change /dev/hda1 to whatever your root filesystem is called The three aforementioned lines should look like this (substitute the appropriate values):
server_address=client_private_IP
allowed_hosts=nagios_server_private_IP
command[check_hda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/vda Note that there are several other "commands" defined in this file that will run if the Nagios server is configured to use them. Also note that NRPE will be listening on port 5666 because server_port=5666 is set.
If you have any firewalls blocking that port, be sure to open it to your Nagios server. Save and quit. Restart NRPE Restart NRPE to put the change into effect:
sudo service nagios-nrpe-server restart
Once you are done installing and configuring NRPE on the hosts that you want to monitor, you will have to add these hosts to your Nagios server configuration before it will start monitoring them. Add Host to Nagios Configuration On your Nagios server, create a new configuration file for each of the remote hosts that you want to monitor in /usr/local/nagios/etc/servers/. Replace the highlighted word, "yourhost", with the name of your host:
sudo vi /usr/local/nagios/etc/servers/yourhost.cfg
Add in the following host definition, replacing the host_name value with your remote hostname ("web-1" in the example), the alias value with a description of the host, and the address value with the private IP address of the remote host:
define host {
use linux-server
host_name yourhost
alias My first Apache server
address 10.132.234.52
max_check_attempts 5
check_period 24x7
notification_interval 30
notification_period 24x7
}
With the configuration file above, Nagios will only monitor if the host is up or down. If this is sufficient for you, save and exit then restart Nagios. If you want to monitor particular services, read on. Add any of these service blocks for services you want to monitor. Note that the value of check_command determines what will be monitored, including status threshold values. Here are some examples that you can add to your host's configuration file: Ping:
define service {
use generic-service
host_name yourhost
service_description PING
check_command check_ping!100.0,20%!500.0,60%
} SSH (notifications_enabled set to 0 disables notifications for a service):
define service {
use generic-service
host_name yourhost
service_description SSH
check_command check_ssh
notifications_enabled 0
}
If you're not sure what use generic-service means, it is simply inheriting the values of a service template called "generic-service" that is defined by default.
And now check the configuration: /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
... to see if the configuration is correct.
Now save and quit. Reload your Nagios configuration to put any changes into effect: Sudo service apache2 restart sudo service nagios restart
sudo service nagios reload
Once you are done configuring Nagios to monitor all of your remote hosts, you should be set. Be sure to access your Nagios web interface, and check out the Services page to see all of your monitored hosts and services:
Section 2 – Capstone Exercise
Step 1
Start your Google Compute Engine virtual machine and connect to it using SSH.
sudo ls /usr/local/nagios/etc/servers
sudo nano /usr/local/nagios/etc/servers/devops-host.cfg
Step 2
Add code
define service {
use generic-service
host_name devops-host
service_description CHECKJAVA
check_command check_java
notifications_enabled 0
}
define service
{
use generic-service
host_name devops-host
service_description CHECKTOMCAT
check_command check_tomcat
notifications_enabled 0
}
define service
{
use generic-service
host_name devops-host
service_description CHECKTOMCATAPP
check_command check_TomcatApplication -u admin -p admin -h http://localhost -P $
notifications_enabled 0
}
Step 3
Save the file and exit.
Step 4
sudo service apache 2 restart
sudo service nagios restart
Step 5
Go to your browser and open the Nagios page
http://nagios_server_public_ip/nagios
• Plugins are compiled executables or scripts(Perl or non-Perl) that extends Nagios functionality to monitor servers and hosts
• Nagios will execute a Plugin to check the status of a service or host
• Nagios can be compiled with support for an embedded Perl interpreter to execute Perl plugins
• Without it, Nagios executes Perl and non-Perl plugins by forking and executing the plugins as an external command
Nagios Remote Plugin Executor (NRPE)
• NRPE allows you to remotely execute Nagios plugins on other Linux/Unix machines. This allows you to monitor remote machine metrics such as disk usage, CPU load etc
• It can communicate with some of the Windows agent addons, so you can execute scripts and check metrics on remote Windows machines as well
Nagios Remote Data Processor
• Nagios Remote Data Processor (NRDP) is an agent which allows flexible data transport
• It uses standard protocols such as: https:// , XML
• The decision to send out notifications is made in the service check and host check logic
• Each host and service definition has a <contact_groups> option that specifies what contact groups receive notifications for that particular host or service
• There are several filters that notifications encounters before reaching to the receiver
Prerequisites for delivering notification
Nagios supports optional detection of hosts and services that are "flapping"
Flapping occurs when a service or host changes state too frequently, resulting a problem and recovery notifications
Nagios Notification Methods
• There are many ways through which Nagios notifies about a problem or recovery Example: Mail, Instant message, Audio alert etc.
• How notifications are sent depend on the notification commands that are defined in your object definition files
• While writing your notification commands, you need to take into account what type of notification is occurring
• The $NOTIFICATIONTYPE$ macro (macroinstruction)contains a string that identifies the type of notification occurring
Program Wide Filters
• Filter to test of whether or not notifications are enabled on a program-wide basis
• This is initially determined by the enable_notifications directive in the main config file
• If notifications are disabled on a program-wide basis, no host or service notifications can be sent out or else notifications move to the next filter
Service & Host Filters
• This filter is a check to see if
• The host or service is in a period of scheduled downtime
• The host or service is flapping
• Notifications can be sent out for warning states, critical states, and recoveries
• Notifications fall in valid notification time period
• Scheduled downtime- Scheduled periods of planned downtime for hosts and service that you're monitoring.
• This is an event of taking a server down for an upgrade, etc.
Contact Filter
At this point the notification has passed the program mode filter and all host or service filters and Nagios starts to notify all the people it should
Contact filters are specific to each contact and do not affect other contacts receive notifications
Git is an open source Distributed Version Control System(DVCS) which records changes made to the files laying emphasis on speed, data integrity and distributed, non-linear workflows.
Here are the Git installation commands for different operating systems:
Commands | Description |
|---|---|
| Git for Windows stand-alone installer. | |
| $ brew install git | Install Git with Homebrew on Mac OS |
| $ sudo port selfupdate | Install Git with MacPorts on Mac OS |
| $ sudo apt-get install git | Install Command for Linux |
| $ git –version | Shows the current version of your Git |
Here are Git configuration and setup commands:
Commands | Description |
|---|---|
| git config –global user.name “Your Name” | Set your username globally. |
| git config –global user.email “youremail@example.com” | Set your email globally. |
| git config –global color.ui auto – | Set to display colored output in the terminal |
| git help | Display the main help documentation, showing a list of commonly used Git commands. |
Here are the Git initializing a repository commands:
Commands | Description |
|---|---|
| git init | Initializes a new Git repository in the current directory. |
| git init <directory> | Creates a new Git repository in the specified directory. |
| git clone <repository_url> | this Clones a repository from a remote server to your local machine. |
| git clone –branch <branch_name> <repository_url> | Clones a specific branch from a repository. |
Here are some basic Git commands:
Commands | Description |
|---|---|
| git add <file> | Adds a specific file to the staging area. |
| git add . or git add –all | Adds all modified and new files to the staging area. |
| git status | Shows the current state of your repository, including tracked and untracked files, modified files, and branch information. |
| git status –ignored | Displays ignored files in addition to the regular status output. |
| git diff | Shows the changes between the working directory and the staging area (index). |
| git diff <commit1> <commit2> | Displays the differences between two commits. |
| git diff –staged or git diff –cached | Displays the changes between the staging area (index) and the last commit. |
| git diff HEAD | Display the difference between the current directory and the last commit |
| git commit | Creates a new commit with the changes in the staging area and opens the default text editor for adding a commit message. |
| git commit -m “<message>” or git commit –message “<message>” | Creates a new commit with the changes in the staging area and specifies the commit message inline. |
| git commit -a or git commit –all | Commits all modified and deleted files in the repository without explicitly using git add to stage the changes. |
| git notes add | Creates a new note and associates it with an object (commit, tag, etc.). |
| git restore <file> | Restores the file in the working directory to its state in the last commit. |
| git reset <commit> | Moves the branch pointer to a specified commit, resetting the staging area and the working directory to match the specified commit. |
| git reset –soft <commit> | Moves the branch pointer to a specified commit, preserving the changes in the staging area and the working directory. |
| git reset –hard <commit> | Moves the branch pointer to a specified commit, discarding all changes in the staging area and the working directory, effectively resetting the repository to the specified commit. |
| git rm <file> | Removes a file from both the working directory and the repository, staging the deletion. |
| git mv | Moves or renames a file or directory in your Git repository. |
Also, check: Basic Git Commands with Examples
Here are some of the updated commands for Git commit:
Commands | Description |
| git commit -m “feat: message” | Create a new commit in a Git repository with a specific message to indicate a new feature commit in the repository. |
| git commit -m “fix: message” | Create a new commit in a Git repository with a specific message to fix the bugs in codebases |
| git commit -m “chore: message” | Create a new commit in a Git repository with a specific message to show routine tasks or maintenance. |
| git commit -m “refactor: message” | Create a new commit in a Git repository with a specific message to change the code base and improve the structure. |
| git commit -m “docs: message” | Create a new commit in a Git repository with a specific message to change the documentation. |
| git commit -m “style: message” | Create a new commit in a Git repository with a specific message to change the styling and formatting of the codebase. |
| git commit -m “test: message” | Create a new commit in a Git repository with a specific message to indicate test-related changes. |
| git commit -m “perf: message” | Create a new commit in a Git repository with a specific message to indicate performance-related changes. |
| git commit -m “ci: message” | Create a new commit in a Git repository with a specific message to indicate the continuous integration (CI) system-related changes. |
| git commit -m “build: message” | Create a new commit in a Git repository with a specific message to indicate the changes related to the build process. |
| git commit -m “revert: message” | Create a new commit in a Git repository with a specific message to indicate the changes related to revert a previous commit. |
Here are some Git branching and merging commands:
Commands | Description |
|---|---|
| git branch | Lists all branches in the repository. |
| git branch <branch-name> | Creates a new branch with the specified name. |
| git branch -d <branch-name> | Deletes the specified branch. |
| git branch -a | Lists all local and remote branches. |
| git branch -r | Lists all remote branches. |
| git checkout <branch-name> | Switches to the specified branch. |
| git checkout -b <new-branch-name> | Creates a new branch and switches to it. |
| git checkout — <file> | Discards changes made to the specified file and revert it to the version in the last commit. |
| git merge <branch> | Merges the specified branch into the current branch. |
| git log | Displays the commit history of the current branch. |
| git log <branch-d | Displays the commit history of the specified branch. |
| git log –follow <file> | Displays the commit history of a file, including its renames. |
| git log –all | Displays the commit history of all branches. |
| git stash | Stashes the changes in the working directory, allowing you to switch to a different branch or commit without committing the changes. |
| git stash list | Lists all stashes in the repository. |
| git stash pop | Applies and removes the most recent stash from the stash list. |
| git stash drop | Removes the most recent stash from the stash list. |
| git tag | Lists all tags in the repository. |
| git tag <tag-name> | Creates a lightweight tag at the current commit. |
| git tag <tag-name> <commit> | Creates a lightweight tag at the specified commit. |
| git tag -a <tag-name> -m “<message>” | Creates an annotated tag at the current commit with a custom message. |
Here are some Git remote repositories commands:
Commands | Description |
|---|---|
| git fetch | Retrieves change from a remote repository, including new branches and commit. |
| git fetch <remote> | Retrieves change from the specified remote repository. |
| git fetch –prune | Removes any remote-tracking branches that no longer exist on the remote repository. |
| git pull | Fetches changes from the remote repository and merges them into the current branch. |
| git pull <remote> | Fetches changes from the specified remote repository and merges them into the current branch. |
| git pull –rebase | Fetches changes from the remote repository and rebases the current branch onto the updated branch. |
| git push | Pushes local commits to the remote repository. |
| git push <remote> | Pushes local commits to the specified remote repository. |
| git push <remote> <branch> | Pushes local commits to the specified branch of the remote repository. |
| git push –all | Pushes all branches to the remote repository. |
| git remote | Lists all remote repositories. |
| git remote add <name> <url> | Adds a new remote repository with the specified name and URL. |
Here are some Git comparison commands:
Commands | Description |
|---|---|
| git show | Shows the details of a specific commit, including its changes. |
| git show <commit> | Shows the details of the specified commit, including its changes. |
Here are some Git managing history commands:
Commands | Description |
|---|---|
| git revert <commit> | Creates a new commit that undoes the changes introduced by the specified commit. |
| git revert –no-commit <commit> | Undoes the changes introduced by the specified commit, but does not create a new commit. |
| git rebase <branch> | Reapplies commits on the current branch onto the tip of the specified branch. |
Here are some of the reasons why you might want to use Git:
In conclusion, This Git Cheat Sheet is thoughtfully organized and categorized, making it easy for developers to quickly find the commands they need for specific use cases. Whether it’s configuring and setting up Git, creating and managing projects, taking snapshots, branching and merging, sharing and updating, comparing changes, or managing version history, the Git Cheat Sheet covers it all.
By utilizing this resource, developers can enhance their productivity and efficiency in working with Git, ultimately leading to smoother and more successful software development projects.
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