How to uninstall nextcloud from Ubuntu ?
July 8, 2020 Leave a comment
If the nextcloud is installed using snap command, then use the following command to uninstall or remove nextcloud.
sudo snap remove nextcloudHTTPS to HTTPS proxy in Apache Server
June 23, 2020 Leave a comment
Add the following configurations to the virtual host to enable https to https proxy in Apache Web Server.
SSLProxyEngine on
SSLProxyVerify none
SSLProxyCheckPeerCN off
SSLProxyCheckPeerName off
SSLProxyCheckPeerExpire offYou may get the following error if these configurations are not added to the virtual host “Error during SSL Handshake with remote server”
How to use password with special character in mount command linux ?
May 22, 2020 Leave a comment
I faced a problem while using mount command with a password containing special characters. The error that I got was “permission denied”. On analyzing the root cause, I figured out that because of the special character, the authentication failed.
The syntax of the mount command is given below.
> mount -t cifs -o username= ,password=[password] [windows-share-dir-path] [dir-in-linux]
Here my password was something like below. It has so many special characters.
> i2_Gw$wF?Xs4zq??K
Solution
The solution is simple. Create a text file and enter the credentials into that file.
I have created a file with the name credentials.ini
username=[username] password=[password]
Now save this file and use this credentials file in the mount command. The syntax is given below.
mount -t cifs -o credentials=credentials.ini [windows-share-dir-path] [dir-in-linux]
Now execute this command and your problem will be solved. !!!!
rpm: /usr/bin/rpmspec: No such file or directory – CentOS RHEL
May 21, 2020 Leave a comment
I have faced an issue while building an rpm in a CentOS machine. The error was rpm: /usr/bin/rpmspec: No such file or directory. To fix this issue we need to install the following package and re-run the build.
For CentOS 7 or RHEL 7 users
> sudo yum install rpm-build
For CentOS 8 or RHEL 8 users
> sudo dnf install rpm-build
How to install Python in CentOS 8 / RHEL 8 ?
May 21, 2020 Leave a comment
Python is not available by default in CentOS 8 / RHEL 8. Read the following blog post to install Python and pip in CentOS 8 / RHEL 8.
To Install Python 3 in CentOS 8 or RHEL 8
> sudo dnf install python3
CentOS 8 and RHEL 8 does not have an unversioned python by default. We have to explicitly set it. So simply typing python will give you a “command not found” response. To verify the installation, use the following command
> python3 -V
The above command will print the version information. For me it printed Python 3.6.8
To install pip, execute the following command
> sudo dnf install python3-pip
Check the installation
> pip3 –version
If you simply type the command python in the shell, it will give you a response something like below
bash: python: command not found…
To enable the command python, execute the following command.
> sudo alternatives –set python /usr/bin/python3
This will enable command python. Now you can use python without explicitly typing the version.
Note: Follow the below steps only if you need Python 2. If your requirement if Python3, refer the steps described above.
To Install Python 2 in CentOS 8 or RHEL 8
> sudo dnf install python2
To install pip, execute the following command
> sudo dnf install python2-pip
Now check the installation
> pip2 –version
To set python2 as the default python across the system, execute the following command.
> sudo alternatives –set python /usr/bin/python2
In previous versions of CentOS and RHEL , there were so much dependency in the system with the unversioned python. Installing Python 3 and Python 2 together creates so much mess in the system. Now in CentOS 8 and RHEL 8, it is very easy.
Hope this blog helps. Please comment below if you face any issues. 🙂
How to set url length in Nginx Request (error code: 414, uri too large)
May 15, 2020 Leave a comment
Today I got one annoying error after deploying the new version of the web application in nginx web server. Initially I thought the web app was buggy, but when I inspected the requests and response, I found the following error.
error code: 414, uri too large
On checking more details around this, I found that this issue can be fixed by adjusting few configurations in nginx. The parameter to modify is large_client_header_buffers.
This parameter sets the maximum number and size of buffers used for reading large client request header. A request line cannot exceed the size of one buffer, or the 414 (Request-URI Too Large) error is returned to the client. A request header field cannot exceed the size of one buffer as well, or the 400 (Bad Request) error is returned to the client. Buffers are allocated only on demand. By default, the buffer size is equal to 8K bytes. If after the end of request processing a connection is transitioned into the keep-alive state, these buffers are released.
Syntax : large_client_header_buffers number size ;
The default value is 4 and the size is 8 KB. You can increase this value to a higher value to fix this issue.
large_client_header_buffers 16 128k;
If you are facing issues even after making these changes, then add the following configuration to the server block in nginx.
fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;
client_max_body_size 24M;
client_body_buffer_size 128k;
client_header_buffer_size 5120k;
large_client_header_buffers 16 5120k;
Hope this helps 🙂 Please comment if you are facing any issues.
How to enable Compression in Nginx
May 15, 2020 Leave a comment
If you are using Nginx webserver, you have to try this out. I started exploring for this option when I faced slowness in rending the pages in one of the applications. When I checked the backend services, the web service API was given the responses quickly, but the page was taking more time to load. On further inspection, I figured out that the API was sending a a data of size 5 MB. So the browser will first download this data and this speed depends on the bandwidth.
I explored further and figured out the way of compressing API body using the webserver. This will speed up the API calls as the data transferred over the network will be very less. In my case, the 5 MB data became few KBs (size of compressed data). This will get extracted quickly in the browser and it gets rendered in the screen.
The required configurations are pasted below for quick reference.
Make the changes in the config file /etc/nginx/nginx.conf. Add the following content to the nginx.conf file.
gzip on; gzip_vary on; gzip_min_length 1024; gzip_proxied expired no-cache no-store private auth; gzip_types text/plain text/css text/xml text/javascript application/x-javascript application/xml; gzip_disable "MSIE [1-6]\.";
The explanation of each of the parameters are given below.
- gzip on; – enables gzip compression in nginx
- gzip_vary on: – tells proxies to cache both compressed and normal versions of a resource
- gzip_types – The type of files that can be compressed
- gzip_disable “MSIE [1-6]\.”; – Disable compression for Internet Explorer versions 1-6
- gzip_min_length 1024; – Nginx will compress the files greater than this size and it will not compress anything less than this size.
- gzip_proxied – compress data even for clients that are connecting via proxies
This is one of the way to improve the performance of APIs. The developers can focus on enhancing their logic and the admin or DevOps engineer can focus on enhancing the web server with optimal configuration. There are so many tricks and magics we can do in the web server. I will try to post some of those in my blog.
Hope this helps. 🙂 . Please comment if you face any issues.
Production deployment of a Python Web Service (Flask / Tornado Application)
May 3, 2020 Leave a comment
Python Flask and Tornado are two of the most popular frameworks in python for developing RESTful services.
Do you know how to develop and deploy a production grade python application. ?
A sample python flask service is given below. This is a sample flask web service. This has only one endpoint (/requestme) at is a GET method. (sample_flask.py). I am not focusing on the coding standards. My goal is to show you the production implementation of a python application.
We can run this program in the command line by executing the following command.
> python sample_flask.py
The service will be up and running in port 9090. You will be able to make requests to the application by using the URL http://ipaddress:9090/requestme.
How many requests will this python web service can handle ?
10 or 20 or 100 ?? … Any guess ??
Definitely this is not going to handle too many requests. This is good for development trials and experimental purpose. But we cannot deploy something like this in production environment.
How to scale python applications ?
Refer to the below diagram. The diagram has multiple instances of flask applications with Gunicorn WSGI proxied and load balanced through Nginx web server.
Production Deployment of Python Flask Application
Sample Nginx configuration that implements the reverse proxy and load balancing is given below.
This is a sample configuration and this does not have the advanced parameters.
server {
listen 80;
server_name myserverdomain
location / {
proxy_pass http://upstream_backend/requestme;
}
}
upstream backend {
server gunicornapplication1:8080;
server gunicornapplication2:8080;
}
The upstream section routes the requests to the two gunicorn backends and the requests are routed in round robin manner. We can add as many backend servers as we need based on the load.
How to run the python applications with gunicorn ?
First lets install gunicorn
> pip install gunicorn
Now it is simple, run the following command.
> gunicorn -w 4 app:app
Now the our application will run with 4 workers. Each worker is a separate process and will be able to handle requests. The gunicorn will take care of handling the requests between each of the workers.
We can start multiple gunicorn instances like this and keep it behind the nginx. This is the way to scale our python applications.
Hope this helps 🙂
Route internet traffic through a specific interface in Linux Servers – CentOS / RHEL
April 29, 2020 Leave a comment
I have a server with multiple network interfaces. Out of that two of them were connected to two different networks. My requirement is to route the internet traffic through the second interface. The Server is running with CentOS 7 operating system. The second interface is connected to a network with higher internet bandwidth and the first interface is connected to a network with lower bandwidth. So I have to make the second interface as the primary/default interface.
The details of the network interfaces are given below.
Details of first interface:
Interface name -> eno2
IP Address: 192.168.0.208
Gateway 192.168.0.1
Internet Provider : ISP01
Details of second interface:
Interface name -> eno3
IP Address: 172.31.0.208
Gateway 172.31.0.1
Internet Provider : ISP02
The diagrammatic view of the server and network connections are given below.
Problem statement:
The internet traffic is going through the first interface. I want to change it to the second interface.
How to check the route of the internet traffic ?
This can be checked by using the traceroute command. Execute the following commands and check hops. If it is going through the gateway of the first network, means traffic is routed through the first interface. If it is going through the gateway of the second network, means that the traffic is routed through the second interface.
traceroute google.com
When I executed this command, I got the following output that proves that the traffic was going through the first interface. 192.168.0.1 is the gateway of the first interface. You can see the details in the below screenshot.
How to list the default traffic routes ?
To list the existing routes in the system, type the following command in the terminal.
ip route list
This will list all the routes and that shows the default routes also. The following screenshot shows the details of the routes in my system.
In the above image, you can see two default routes. The first one has a priority of 102 and second one with priority 103. So based on the priority, the traffic goes through the first interface (gateway 192.168.0.1, ISP-01).
How to change the default / primary route ?
In my case there were two default routes. So making one interface as the default or primary route will solve the problem.
This can be enabled by configuring the DEFROUTE parameter in the network interface settings. The network interface configurations are present in the following directory.
/etc/sysconfig/network-scripts
In this directory, you can see files that starts with ifcfg-. In my case, the two files that I have to deal with are ifcfg-eno2 and ifcfg-eno3.
In this file, there will be a parameter DEFROUTE. If it is configured with value “yes” means that interface is a default route. If the value is “no” means it is not a default interface.
So make DEFROUTE=no in the first interface (ifcfg-eno2) and DEFROUTE=yes in the second interface (ifcfg-eno3).
Restart the network after making these changes. The command is shared below.
service network restart
Now check the route list and see the default route/s. The command is given below.
ip route list
The screenshot from my system is shared below.
Now you can see that the second interface (gateway 172.31.0.1 & ISP-02) became the default interface and the first interface got removed from the default list. It is present in the available interfaces, but not the default interface.
Now let us test the internet traffic through traceroute command. As per our configuration, the traffic should go through the second interface. The command is given below.
traceroute google.com
The screenshot from my system is given below.
As per the screenshot, the traffic is going as expected based on our configuration. It is going through the second interface.
The steps for Ubuntu and other operating systems are also similar. Here I have explained based on CentOS & RHEL operating systems.
Hope this article helps someone. 🙂
bash: ifconfig: command not found debian centos ubuntu rhel
April 27, 2020 Leave a comment
This article will be helpful for Ubuntu, CentOS, RHEL, Debian, Raspbian OS users.
ifconfig is a very commonly used command to find the ipaddress of a linux machine. Sometimes we may get an error like
bash: ifconfig: command not found
The reason for this can be because of one of the following reasons.
- The ifconfig command is not available in the system.
- In case of this issue, we have to install the net-tools package
- The ifconfig script is not available in the PATH
- In this case, we have to try executing /sbin/ifconfig command
In these cases, we can get the ip address details by using another command. We don’t have to install any additional package for issuing the following command
ip addr
If the net-tools package is missing in the system, we can enable ifconfig by installing the package. The command to install the package is given below.
For Ubuntu, Raspbian, Debian OS use the following command
sudo apt-get install net-tools
For RHEL / CentOS users, use the following command
sudo yum install net-tools
Now try ifconfig in the commandline and you will be able to see the ip address details.
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