How To Create a SSL Certificate on Apache for Ubuntu 14.04

using openSSL


using Let’s Encrypt signed method

How To Add Swap Space on Ubuntu

Nice article courtsey : digital ocean



One of the easiest way of increasing the responsiveness of your server and guarding against out-of-memory errors in applications is to add some swap space. In this guide, we will cover how to add a swap file to an Ubuntu 16.04 server.


Although swap is generally recommended for systems utilizing traditional spinning hard drives, using swap with SSDs can cause issues with hardware degradation over time. Due to this consideration, we do not recommend enabling swap on DigitalOcean or any other provider that utilizes SSD storage. Doing so can impact the reliability of the underlying hardware for you and your neighbors. This guide is provided as reference for users who may have spinning disk systems elsewhere.

If you need to improve the performance of your server on DigitalOcean, we recommend upgrading your Droplet. This will lead to better results in general and will decrease the likelihood of contributing to hardware issues that can affect your service.

What is Swap?

Swap is an area on a hard drive that has been designated as a place where the operating system can temporarily store data that it can no longer hold in RAM. Basically, this gives you the ability to increase the amount of information that your server can keep in its working “memory”, with some caveats. The swap space on the hard drive will be used mainly when there is no longer sufficient space in RAM to hold in-use application data.

The information written to disk will be significantly slower than information kept in RAM, but the operating system will prefer to keep running application data in memory and use swap for the older data. Overall, having swap space as a fall back for when your system’s RAM is depleted can be a good safety net against out-of-memory exceptions on systems with non-SSD storage available.

Check the System for Swap Information

Before we begin, we can check if the system already has some swap space available. It is possible to have multiple swap files or swap partitions, but generally one should be enough.

We can see if the system has any configured swap by typing:

  • sudo swapon –show

If you don’t get back any output, this means your system does not have swap space available currently.

You can verify that there is no active swap using the free utility:

  • free -h
              total        used        free      shared  buff/cache   available
Mem:           488M         36M        104M        652K        348M        426M
Swap:            0B          0B          0B

As you can see in the “Swap” row of the output, no swap is active on the system.

Check Available Space on the Hard Drive Partition

The most common way of allocating space for swap is to use a separate partition devoted to the task. However, altering the partitioning scheme is not always possible. We can just as easily create a swap file that resides on an existing partition.

Before we do this, we should check the current disk usage by typing:

  • df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            238M     0  238M   0% /dev
tmpfs            49M  624K   49M   2% /run
/dev/vda1        20G  1.1G   18G   6% /
tmpfs           245M     0  245M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           245M     0  245M   0% /sys/fs/cgroup
tmpfs            49M     0   49M   0% /run/user/1001

The device under /dev is our disk in this case. We have plenty of space available in this example (only 1.1G used). Your usage will probably be different.

Although there are many opinions about the appropriate size of a swap space, it really depends on your personal preferences and your application requirements. Generally, an amount equal to or double the amount of RAM on your system is a good starting point. Another good rule of thumb is that anything over 4G of swap is probably unnecessary if you are just using it as a RAM fallback.

Create a Swap File

Now that we know our available hard drive space, we can go about creating a swap file within our filesystem. We will create a file of the swap size that we want called swapfile in our root (/) directory.

The best way of creating a swap file is with the fallocate program. This command creates a file of a preallocated size instantly.

Since the server in our example has 512MB of RAM, we will create a 1 Gigabyte file in this guide. Adjust this to meet the needs of your own server:

  • sudo fallocate -l 1G /swapfile

We can verify that the correct amount of space was reserved by typing:

  • ls -lh /swapfile
  • -rw-r–r– 1 root root 1.0G Apr 25 11:14 /swapfile

Our file has been created with the correct amount of space set aside.

Enabling the Swap File

Now that we have a file of the correct size available, we need to actually turn this into swap space.

First, we need to lock down the permissions of the file so that only the users with root privileges can read the contents. This prevents normal users from being able to access the file, which would have significant security implications.

Make the file only accessible to root by typing:

  • sudo chmod 600 /swapfile

Verify the permissions change by typing:

  • ls -lh /swapfile
-rw------- 1 root root 1.0G Apr 25 11:14 /swapfile

As you can see, only the root user has the read and write flags enabled.

We can now mark the file as swap space by typing:

  • sudo mkswap /swapfile
Setting up swapspace version 1, size = 1024 MiB (1073737728 bytes)
no label, UUID=6e965805-2ab9-450f-aed6-577e74089dbf

After marking the file, we can enable the swap file, allowing our system to start utilizing it:

  • sudo swapon /swapfile

We can verify that the swap is available by typing:

  • sudo swapon –show
/swapfile file 1024M   0B   -1

We can check the output of the free utility again to corroborate our findings:

  • free -h
              total        used        free      shared  buff/cache   available
Mem:           488M         37M         96M        652K        354M        425M
Swap:          1.0G          0B        1.0G

Our swap has been set up successfully and our operating system will begin to use it as necessary.

Make the Swap File Permanent

Our recent changes have enabled the swap file for the current session. However, if we reboot, the server will not retain the swap settings automatically. We can change this by adding the swap file to our /etc/fstab file.

Back up the /etc/fstab file in case anything goes wrong:

  • sudo cp /etc/fstab /etc/fstab.bak

You can add the swap file information to the end of your /etc/fstab file by typing:

  • echo ‘/swapfile none swap sw 0 0’ | sudo tee -a /etc/fstab

Tweak your Swap Settings

There are a few options that you can configure that will have an impact on your system’s performance when dealing with swap.

Adjusting the Swappiness Property

The swappiness parameter configures how often your system swaps data out of RAM to the swap space. This is a value between 0 and 100 that represents a percentage.

With values close to zero, the kernel will not swap data to the disk unless absolutely necessary. Remember, interactions with the swap file are “expensive” in that they take a lot longer than interactions with RAM and they can cause a significant reduction in performance. Telling the system not to rely on the swap much will generally make your system faster.

Values that are closer to 100 will try to put more data into swap in an effort to keep more RAM space free. Depending on your applications’ memory profile or what you are using your server for, this might be better in some cases.

We can see the current swappiness value by typing:

  • cat /proc/sys/vm/swappiness

For a Desktop, a swappiness setting of 60 is not a bad value. For a server, you might want to move it closer to 0.

We can set the swappiness to a different value by using the sysctl command.

For instance, to set the swappiness to 10, we could type:

  • sudo sysctl vm.swappiness=10
vm.swappiness = 10

This setting will persist until the next reboot. We can set this value automatically at restart by adding the line to our /etc/sysctl.conf file:

  • sudo nano /etc/sysctl.conf

At the bottom, you can add:


Save and close the file when you are finished.

Adjusting the Cache Pressure Setting

Another related value that you might want to modify is the vfs_cache_pressure. This setting configures how much the system will choose to cache inode and dentry information over other data.

Basically, this is access data about the filesystem. This is generally very costly to look up and very frequently requested, so it’s an excellent thing for your system to cache. You can see the current value by querying the proc filesystem again:

  • cat /proc/sys/vm/vfs_cache_pressure

As it is currently configured, our system removes inode information from the cache too quickly. We can set this to a more conservative setting like 50 by typing:

  • sudo sysctl vm.vfs_cache_pressure=50
vm.vfs_cache_pressure = 50

Again, this is only valid for our current session. We can change that by adding it to our configuration file like we did with our swappiness setting:

  • sudo nano /etc/sysctl.conf

At the bottom, add the line that specifies your new value:


Save and close the file when you are finished.


Following the steps in this guide will give you some breathing room in cases that would otherwise lead to out-of-memory exceptions. Swap space can be incredibly useful in avoiding some of these common problems.

If you are running into OOM (out of memory) errors, or if you find that your system is unable to use the applications you need, the best solution is to optimize your application configurations or upgrade your server.

How to install odoo 8 on Ubuntu

How to Install PostgreSQL and phpPgAdmin on Ubuntu

Step 1 – Installing PostgreSQL, phpPgAdmin and Apache2

PostgreSQL and PhpPgAdmin are available in the Ubuntu repository. So you just need to install them with the apt command.

sudo apt-get -y install postgresql postgresql-contrib phppgadmin

The above command will automatically install all packages needed by PostgreSQL, like Apache, PHP etc.

Step 2 – Configure PostgreSQL user

PostgreSQL uses role for user authentication and authorization, it just like Unix-Style permissions. By default, PostgreSQL creates a new user called “postgres” for basic authentication. To use PostgreSQL, you need to login to the “postgres” account, you can do that by typing:

sudo su
su – postgres

Now you can access the PostgreSQL prompt with the command:


And then change the password for postgres role by typing:

\password postgres


Then enter \q to leave the psql command line.


exit the postgress user and come back to root or other sudo enabled user

You need to configure apache for phpPgAdmin. Edit the file /etc/apache2/conf-available/phppgadmin.conf with nano by typing:

cd /etc/apache2/conf-available/
nano phppgadmin.conf

Comment out the line #Require local by adding a # in front of the line and add below the line allow from all so that you can access from your browser.


Edit the file /etc/phppgadmin/ by typing :

cd /etc/phppgadmin/

Find the line $conf[‘extra_login_security’] = true; and change the value to false so you can login to phpPgAdmin with user postgres.

scp commands examples to transfer files on Linux

Installing scp

Scp is generally installed by default on most linux distros as a part of openssh packages. On ubuntu/debian for example, the openssh-client package provides the scp program.

$ dpkg -L openssh-client | grep scp

Its the OpenSSH package that provides the ssh, scp, sftp programs along with many other tools. So we do not have to do anything extra in here, except to use and learn the program.

Using scp

The basic syntax of scp is very simple to memorize. It looks like this

$ scp source_file_path destination_file_path

Depending on the host, the file path should include the full host address, port number, username and password along with the directory path.

So if you are “sending” file from your local machine to a remote machine (uploading) the syntax would look like this

$ scp ~/my_local_file.txt

When copying file from remote host to local host (downloading), its looks just the reverse

$ scp ~/my_local_file.txt

# just download the file
$ scp user@ .

That is pretty much about using scp for regular tasks. Apart from it, there are a couple of extra options and functions that scp supports. Lets take a quick overview of those.

And yes, by default scp will always overwrite files on the destination. If you need to avoid that, use a more powerful tool called rsync.

1. Verbose output

With verbose output, the scp program would output lots of information about what it does in the background. This is often useful when the program fails or is unable to complete the request. The verbose output would then indicate the exact point where the program ran into issues.

$ scp -v ~/test.txt root@
Executing: program /usr/bin/ssh host, user root, command scp -v -t /root/help2356.txt
OpenSSH_6.2p2 Ubuntu-6ubuntu0.1, OpenSSL 1.0.1e 11 Feb 2013
debug1: Reading configuration data /home/enlightened/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to [] port 22.
debug1: Connection established.

The output would be big and contain detailed information about how the connection is made, what configuration and identity files are being used and so on.

2. Transfer multiple files

Multiple files can be specified separated by a space like this

$ scp foo.txt bar.txt username@remotehost:/path/directory/

To copy multiple files from remote host to current local directory

$ scp username@remotehost:/path/directory/\{foo.txt,bar.txt\} .

$ scp root@\{abc.log,cde.txt\} .

3. Copy entire directory (recursively)

To copy an entire directory from one host to another use the r switch and specify the directory

$ scp -v -r ~/Downloads root@

4. Copy files across 2 remote hosts

Scp can copy files from 1 remote host to another remote host as well.

$ scp user1@remotehost1:/some/remote/dir/foobar.txt user2@remotehost2:/some/remote/dir/

5. Speed up the transfer with compression

A super cool option to speed up the transfer to save time and bandwidth. All you need to do is use the C option to enable compression. The files are compressed on the fly and decompressed on the destination.

$ scp -vrC ~/Downloads root@

In the above example we moved the entire directory with compression enabled. The speed gain would depend on how much the files could be compressed.

6. Limit the bandwidth usage

If you do not want scp to take up the entire available bandwidth, then use the l option to limit the maximum speed in Kbit/s.

$ scp -vrC -l 400 ~/Downloads root@

7. Connect to a different port number on remote host

If the remote server has ssh daemon running on a different port (default is 22), then you need to tell scp to use that particular port number using the ‘-P’ option.

$ scp -vC -P 2200 ~/test.txt root@

8. Preserve file attributes

The ‘-p’ option (smallcase), would preserve modification times, access times, and modes from the original file.

$ scp -C -p ~/test.txt root@

9. Quiet mode

In quiet mode ( ‘-q’ option ), the scp output would get suppressed, and would disable the progress meter as well as warning and diagnostic messages.

$ scp -vCq ~/test.txt root@

10. Specify identity file

When using key based (passwordless) authentication, you would need to specify the identity file which contains the private key. This option is directly passed to the ssh command and works the same way.

$ scp -vCq -i private_key.pem ~/test.txt root@

11. Use a different ssh_config file

Use the ‘-F’ option to specify a different ssh_config file.

$ scp -vC -F /home/user/my_ssh_config ~/test.txt root@

12. Use different cipher

Scp by default uses the AES cipher/encryption. Sometimes you might want to use a different cipher. Using a different cipher can speed up the transfer process. For example blowfish and arcfour are known to be faster than AES (but less secure).

$ scp -c blowfish -C ~/local_file.txt username@remotehost:/remote/path/file.txt

In the above example we use the blowfish cipher along with compression. This can give significant speed boost depending on available bandwidth.


Although scp is very efficient at transferring file securely, it lacks necessary features of a file synchronisation tool. All it can do is copy paste all the mentioned files from one location to another.

A more powerful tool is Rsync which not only has all functions of scp but adds more features to intelligently synchronise files across 2 hosts. For example, it can check and upload only the modified files, ignore existing files and so on.

how to recover admin password in Odoo

You may change admin password using progresql from the terminal. You just need to do like these

odoo@odedra:~$ psql testing_db
psql (9.1.14)
Type "help" for help.

testing_db=# UPDATE res_users SET password='new_password' WHERE login = 'admin';

where testing_db is database name.

Now login with new password and change user details whatever you want.