Useful Linux commands for beginners

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If you are switching from Windows to Linux based operating system, then it might be difficult in early days to get hang of it. Here are some commands that will be useful.

If you want to find out size of current directory, just type

du -sh

du -sh

2. Check your disk usage

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           388M   12M  377M   3% /run
/dev/sda6       407G   59G  328G  16% /
tmpfs           1.9G   83M  1.9G   5% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/sda2        96M   32M   65M  34% /boot/efi
tmpfs           388M   60K  388M   1% /run/user/1000

$ df -h

Filesystem Size Used Avail Use% Mounted on

udev 1.9G 0 1.9G 0% /dev

tmpfs 388M 12M 377M 3% /run

/dev/sda6 407G 59G 328G 16% /

tmpfs 1.9G 83M 1.9G 5% /dev/shm

tmpfs 5.0M 4.0K 5.0M 1% /run/lock

tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup

/dev/sda2 96M 32M 65M 34% /boot/efi

tmpfs 388M 60K 388M 1% /run/user/1000

3. See all files and directory size in current path

$ ls -lh
total 1.2G
-rw-r--r--  1 deven deven     75K Jul  4  2017 1470493410_1499166814.jpg
drwxrwxr-x 15 deven deven    4.0K Mar 17 11:54 ach-hq
-rw-rw-r--  1 deven deven     35K Jun 28  2017 address.php
drwxrwxr-x  4 deven deven    4.0K Jul 15  2017 bil 2
-rw-rw-r--  1 deven deven    355K Jul 15  2017 bill 2.zip
drwxrwxr-x  3 deven deven    4.0K Jul 29  2017 book_ge_api
-rw-rw-r--  1 deven deven     96K Aug  8  2017 cities.sql
drwxrwxr-x 13 deven deven    4.0K Jun 27  2017 clon

$ ls -lh

total 1.2G

-rw-r--r-- 1 deven deven 75K Jul 4 2017 1470493410_1499166814.jpg

drwxrwxr-x 15 deven deven 4.0K Mar 17 11:54 ach-hq

-rw-rw-r-- 1 deven deven 35K Jun 28 2017 address.php

drwxrwxr-x 4 deven deven 4.0K Jul 15 2017 bil 2

-rw-rw-r-- 1 deven deven 355K Jul 15 2017 bill 2.zip

drwxrwxr-x 3 deven deven 4.0K Jul 29 2017 book_ge_api

-rw-rw-r-- 1 deven deven 96K Aug 8 2017 cities.sql

drwxrwxr-x 13 deven deven 4.0K Jun 27 2017 clon

4. Truncate log files

truncate -s 0 /path-to-log-file/log.log

1	truncate -s 0 /path-to-log-file/log.log

5. List content of a directory using ls command

ls -l

ls -l

6. If you want to know about a command, you can take of man command, for example if you want to go into details of ls command, just type

man ls

man ls

It will give you an output something similar to this

NAME
       ls - list directory contents

SYNOPSIS
       ls [OPTION]... [FILE]...

DESCRIPTION
       List information about the FILEs (the current directory by default).  Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

       Mandatory arguments to long options are mandatory for short options too.

       -a, --all
              do not ignore entries starting with .

       -A, --almost-all
              do not list implied . and ..

       --author
              with -l, print the author of each file

NAME

ls - list directory contents

SYNOPSIS

ls [OPTION]... [FILE]...

DESCRIPTION

List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Mandatory arguments to long options are mandatory for short options too.

-a, --all

do not ignore entries starting with .

-A, --almost-all

do not list implied . and ..

--author

with -l, print the author of each file

I will be updating this with more useful commands as and when I found.

Thanks

Transfer ownership of a Digital Ocean Droplet

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I run a web development agency and most of the time it happens that we create servers for client in our own Digital Ocean account during the development phase. When project gets over we usually transfer the ownership of the droplet to client. I have seen Digital Ocean customers
struggling with the transfer of ownership of droplet.

So here is I am giving a simple step by step guide to transfer a droplet from one Digital Ocean account to another.

Step 1: Take a snapshot of droplet

We need to first take a snapshot of the droplet that you want to transfer. You can either take a live snapshot which doesn’t require shutting down the droplet or to avoid any data loss just power off the droplet before taking snapshot. You can power off the droplet from the control panel or by logging into server through ssh.

Enter the name of snapshot and click on “Take Snapshot” button.

DO Snapshot

Step 2: Enter recipient owner digital account email address

Once the snapshot is ready, click on “Change Owner” option. It will prompt to enter recipient email address. Enter the address of the account to which you want to transfer the droplet.

Step 3: Accept snapshot transfer

Now log into the control panel of the recipient account. Go to Images and then Snapshots. You will see the snapshot that you had transferred to this account. Click on Accept to complete the transfer process.

Step 4: Create a new droplet from snapshot

Since we have the snapshot with us now, we need to create a droplet from this snapshot. To Click on “Create Droplet” option from menu and select the appropriate plan for your droplet, and your droplet is ready!

Install COMODO Postive SSL certificate on Ubuntu

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Comodo offers a wide range of SSL certificates to suit a diverse range of business requirements and budgets.

Follow below steps to install comodo positive ssl certificate on your ubuntu server.

Step 1 – Before applying for a certificate we need to submit Certificate Signing Request (CSR) to Certificate Authority (CA). Run below command on your server

openssl req -new -newkey rsa:2048 -nodes -keyout example_com.key -out example_com.csr

1	openssl req -new -newkey rsa:2048 -nodes -keyout example_com.key -out example_com.csr

* replace example_com with your domain name if you want to

It will ask following details

Organization Name
Organizational Unit
Country Code
State / Province
Locality
Common Name – This is the domain name for which you want to purchase SSL certificate

After providing above mentioned details this command will create two files

example_com.key – Your private key which you need to configure Apache or Nginx
example_com.csr – CSR

Step 2 – Apply for the certificate and provide content of CSR file

Step 3 – After submitting CSR, CA will send you an email on email selected by you. You should get your SSL certificate after verifying your domain.

Your certificate zip file will contain

example_com.crt – Your ssl certificate
AddTrustExternalCARoot.crt – Root CA certificate
COMODORSAAddTrustCA.crt – Intermediate CA certificate
COMODORSADomainValidationSecureServerCA.crt – Intermediate CA certificate

Step 4 – Create a bundle of all crt files

cat www_example_com.crt COMODORSADomainValidationSecureServerCA.crt  COMODORSAAddTrustCA.crt AddTrustExternalCARoot.crt &gt; ssl-bundle.crt

1	cat www_example_com.crt COMODORSADomainValidationSecureServerCA.crt COMODORSAAddTrustCA.crt AddTrustExternalCARoot.crt > ssl-bundle.crt

Step 5 – Configuring Apache web server to serve website over HTTPS

  SSLEngine on
  SSLCertificateFile /etc/ssl/example_com.crt
  SSLCertificateKeyFile /etc/ssl/example_com.key
  SSLCertificateChainFile /etc/ssl/ssl-bundle.crt

SSLEngine on

SSLCertificateFile /etc/ssl/example_com.crt

SSLCertificateKeyFile /etc/ssl/example_com.key

SSLCertificateChainFile /etc/ssl/ssl-bundle.crt

Step 6 (Optional) – Configure Nginx to serve website over HTTPS

server {
    listen 443;

    ssl on;
    ssl_certificate /etc/ssl/ssl-bundle.crt;
    ssl_certificate_key /etc/ssl/example_com.key;
}

server {

listen 443;

ssl on;

ssl_certificate /etc/ssl/ssl-bundle.crt;

ssl_certificate_key /etc/ssl/example_com.key;

}

Install or update nodejs usin NVM in Ubuntu

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Node JS is a JavaScript runtime built on Chrome’s V8 JavaScript engine. Node.js uses an event driven, non-blocking I/O model that makes it lightweight and efficient

Using nvmNVM, which stands for “Node.js version manager” we can install multiple versions of nodejs on Ubuntu.

sudo apt-get update
sudo apt-get install build-essential libssl-dev

1 2	sudo apt-get update sudo apt-get install build-essential libssl-dev

To install or update nvm, you can use the install script using cURL: ( You can find the installation instructions on projects github page https://github.com/creationix/nvm/blob/master/README.md)

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.2/install.sh | bash

1	curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.2/install.sh \| bash

or using Wget:

wget -qO- https://raw.githubusercontent.com/creationix/nvm/v0.33.2/install.sh | bash

1	wget -qO- https://raw.githubusercontent.com/creationix/nvm/v0.33.2/install.sh \| bash

Run the script by running

bash install_nvm.sh

source ~/.profile

bash install_nvm.sh

source ~/.profile

To get the list of available Node.js versions

nvm ls-remote

nvm install 6.0.0

nvm use 6.0.0

node -v

nvm ls-remote

nvm install 6.0.0

nvm use 6.0.0

node -v

React Native Issues

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Recently I started learning React Native to build native mobile applications using React JS. I faced lots of issues while making my first application run on my Ubuntu desktop. Here I am recording issues I faced and the solutions that worked for me, so that beginners like me don’t have to reinvent the wheel.

A problem occurred configuring project ‘:app’.

> SDK location not found. Define location with sdk.dir in the local.properties file or with an ANDROID_HOME environment variable.

Go to your React native Project -> Android
Create a file local.properties
Open the file
paste your Android SDK path like below
- in Windows sdk.dir = C:/Users/USERNAME/AppData/Local/Android/sdk
- in macOS sdk.dir = /Users/USERNAME/Library/Android/sdk
- in linux sdk.dir = /home/USERNAME/Android/Sdk

Replace USERNAME with your user name

Now, Run react-native run-android in your terminal

Ref – https://stackoverflow.com/questions/32634352/react-native-android-build-failed-sdk-location-not-found

ENOENT: no such file or directory, open ‘android/app/src/main/assets/index.android.bundle’

Manually create this directory

mkdir android/app/src/main/assets

Unable to load script from assets index.android.bundle

(in project directory) mkdir android/app/src/main/assets
react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res
react-native run-android

ou can automate the above steps by placing them in scripts part of package.json like this:

<span class="str">"android-linux"</span><span class="pun">:</span> <span class="str">"react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res &amp;&amp; react-native run-android"</span>

1	<span class="str">"android-linux"</span><span class="pun">:</span> <span class="str">"react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res && react-native run-android"</span>

Ref: https://stackoverflow.com/questions/44446523/unable-to-load-script-from-assets-index-android-bundle-on-windows

Then you can just execute npm run android-linux from your command line every time.

I will keep updating this as and when I encounter new issues with solutions that worked for me.

Convert GMT to Local timezone in PHP

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Following code snippet converts a date time in GMT to Local timezone.

$myDateTime = new DateTime('2014-08-27 18:21', new DateTimeZone('GMT'));
$myDateTime->setTimezone(new DateTimeZone('America/New_York'));
echo $myDateTime->format('Y-m-d H:i');

$myDateTime = new DateTime('2014-08-27 18:21', new DateTimeZone('GMT'));

$myDateTime->setTimezone(new DateTimeZone('America/New_York'));

echo $myDateTime->format('Y-m-d H:i');

mysql table is marked as crashed and last (automatic?) repair failed

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If you are getting this error

mysql table is marked as crashed and last (automatic?) repair failed

Go to your data folder and try running

myisamchk -r <table_name>.

1	myisamchk -r <table_name>.

You should stop MySQL process first. If that doesn’t work, you can try with

myisamchk -r -v -f <table_name>.

1	myisamchk -r -v -f <table_name>.

I had to navigate to /var/lib/mysql/<database> and run myisamchk -r -v -f ./<table name>.

PS – This was answered at following thread, this post is for just personal reference in future.

Reference – http://stackoverflow.com/questions/8843776/mysql-table-is-marked-as-crashed-and-last-automatic-repair-failed

Requires Doctrine DBAL Laravel migration

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If you are running a migration to change the data type of a column in a table. You might come across this error message in terminal.

[RuntimeException]                                                           
  Changing columns for table "***" requires Doctrine DBAL; install "doctrine/  
  dbal".

[RuntimeException]

Changing columns for table "***" requires Doctrine DBAL; install "doctrine/

dbal".

This error message is telling you to install doctrine/dbal to make this work. You can learn more about this package here https://github.com/doctrine/dbal

To install this package through composer, run following command in terminal.

composer require doctrine/dbal

1	composer require doctrine/dbal

Now you can run your migration by running

php artisan migrate

1	php artisan migrate

This should work now.

npm install – Please try running this command again as root/Administrator

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If you are getting this error while running npm install, then you are not having write permission on .npm directory.

To get the ownership of this directory run following command

sudo chown -R $(whoami) ~/.npm

1	sudo chown -R $(whoami) ~/.npm

Also we need to give write permission to node_modules directory

sudo chown -R $USER /usr/local/lib/node_modules

1	sudo chown -R $USER /usr/local/lib/node_modules

ref – http://stackoverflow.com/questions/16151018/npm-throws-error-without-sudo

Nginx + Php5-fpm error: connect() to unix:/var/run/php5-fpm.sock failed

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I was getting this error in my error log, after searching for solutions online I stumbled upon this solution that worked for me. I am writing this post for my personal reference, it would be great if someone gets benefited by this.

Continue reading →

Devendra Verma

Programming blog, Tutorials, Tips and Tricks

Useful Linux commands for beginners

Transfer ownership of a Digital Ocean Droplet

Install COMODO Postive SSL certificate on Ubuntu

Install or update nodejs usin NVM in Ubuntu

React Native Issues

Convert GMT to Local timezone in PHP

mysql table is marked as crashed and last (automatic?) repair failed

Requires Doctrine DBAL Laravel migration

npm install – Please try running this command again as root/Administrator

Nginx + Php5-fpm error: connect() to unix:/var/run/php5-fpm.sock failed