5. Test the installation by fetching and running test image:
sudo docker run hello-world
For more information, you can visit: https://docs.docker.com/install/linux/docker-ce/ubuntu/
Notes:
1. when having problems with the socket docker binds on you can allow your user to be owner of the socket: sudo chown $USER:docker /var/run/docker.sock
2. If you want to run docker without sudo, just add docker group to the users with: usermod -aG docker $USER
and change the current running group with: newgrp docker
or su ${USER}
3. If you get: ERROR: Couldn't connect to Docker daemon at http+docker://localhost - is it running?
check out the docker service status: sudo systemctl status docker
if it is stopped and masked: Loaded: masked (Reason: Unit docker.service is masked.) then you need to unmask the service: sudo systemctl unmask docker
then again start the docker service: sudo systemctl start docker
until you see sudo systemctl status docker: Active: active (running)
In order to offer more than one service from a single IP address, Linux uses the notion of PORTS. For example, 80 is the common name of port for HTTP, 21 - FTP, 443 - ssh. Users can connect to services by typing the service IP address and its specific port number. Firewalls help us to open and close ports for specific IP addresses or whole network subnets. This is suitable when we want certain IP addresses to have access to our server while its default access to stay restricted.
For video information on firewalls, you can check this course.
In ubuntu, the firewall wrapper is named uncomplicated firewall or in short "ufw". It is installed in Ubuntu by default but is not active. We can check the status of ufw with: "status". If we want to completely isolate access to our machine we could use: "default deny incoming", while: "default allow outgoing" will allow packets to exit our machine. Keep in mind that in order for them to work, we have to activate those rules by typing: "enable". Next, we can explicitly: "reject out ssh" and then "delete reject out ssh".
Hint: If we are unsure of our actions we can always type: "reset" to empty the firewall rules. To deactivate the firewall please use "disable".
Since we are already connected with SSH, if we enable the firewall we will lose our connection so let's allow the forwarded port 22/tcp by typing: sudo ufw allow 22/tcp and run: sudo ufw enable.
We can actually show rules with numbers: status numbered, and to delete a rule we use: "delete rule_number". In order to insert a rule at a particular place, we use: "insert 1 your_rule".
Here are some commonly used service names: secure shell: ssh, mail: smtp, web server: http, https, SAMBA/File sharing: 139/tcp, 445/tcp. Not common service names are hard to remember, so here is a trick: ufw reads from /etc/services. When certain service is installed in order to communicate with the outside word it could modify the firewall rules by adding its own rules. In such cases with "app list" we can see all the installed service /application profiles and "app info 'SSH'" will dig us deeper into what ports certain application profile allows.
Lets' see the following examples on practical usage of the firewall:
//deny all incoming connections from 10.0.0.1 to interface eth0
deny in on eth0 from 10.0.0.1
// limit ssh access of specific IP address
deny proto tcp from 10.0.0.1 to any port 22
// limit a whole subnet
allow from 10.0.0.0/24 to any port 22
// allow ssh access only to IP: 10.0.0.1
allow proto tcp from any to 10.0.0.1 port 22
// deny outgoing SMTP traffic
deny out 25
// allow connections on eth1 interface to MySQL
allow in on eth1 to any port 3306
If we want to use filtering my mac address we can add: -A ufw-before-input -m mac –mac-source 00:00:00:00:00:AA -j DROP in /etc/ufw/before.rules
(these are rules who are read and act before the firewall rules)
To monitor the usage of the firewall we can use: sudo tail -f /var/log/ufw.log, but just if the "ufw logging" is enabled.
While experimenting with the firewall you can use an external network scanner such as Nmap (sudo apt install nmap) to check which ports are open on the machine.
More useful examples you can find with: man ufw
as well as on the ubuntu firewall page: https://help.ubuntu.com/lts/serverguide/firewall.html
More information, you can find in this course.
The following are working examples for managing files, directories, users and groups in Ubuntu server environment.
For more information you can take a look at this course on ubuntu linux server:
Work with the console:
By typing "History" without the quotes, you can take a look at your previous commands and with "history | grep name_of_command " you can search for specific command that you already used. If you want to return the previously used command just press the "up" arrow. And if you have problems remembering filenames you can start typing the first letter of the name and then press several times "TAB" button - this will give you autocomplete for the rest of the word.
You can clear the console by using "clear".
Directories:
All the directories are contained into the root directory /. Pay attention: Linux file and directory names are case sensitive, so "Linux.txt" is different than "linux.txt".
If you want to see your current directory just type: "pwd". With "cd .." you go up to the parent directory, with "cd /" you will go to the root directory. Using the command "ls" you can see the current objects(files, directories and symbolic links) residing in the file system.
You can create directories using mkdir new_dir_name
To delete directory use: rm dir_name . Before removing a directory, please make sure that it is empty.
"ls -la" will give you more information like properties, date of creation, size, permissions, owner and grop of the files and directories.
if you go to the root / directory: "cd /" "ls -la |grep bin" will show you not only the /bin directory but any directories that start with "bin" characters. We can also use * to show all files starting with 'linux': "ls linux*" or listing all .html files "ls .html"
If you want to know more about the "ls" command just append "--help" next to it:
"ls --help"
and if you want to list the resulting information in pages you can type:
"ls --help | more"
"Enter" and "Space" keys can be used for navigation
For more information on the command try: "man ls". You can exit the help screen with the key "q"
Files:
You can create an empty file with the command "touch file_name.txt". To see the contents of the file just type: cat file_name.txt
In just one line we can actually filter the contents of a file based on condition (all the lines containing "Example"), and output them in a new file(output.txt): "cat examples.desktop | grep "Example" > output.txt "
To remove the file we type: "rm output.txt"
We can edit files with the "nano" editor: "nano output.txt" Inside we can use crtl + O to write the changes, and ctrl + X to exit the editor
Hint: if there are spaces or special symbols in the filename to work with it, just wrap the name with quotes or just to put / before the special symbol:
“123–!.txt”
123-\’.txt \‘file name!\’
file\ name\!
Hint: a convenient way of displaying text files is with "more /var/log/syslog" - this will give us the content paginated and if we use: watch tail /var/log/syslog we can watch if there are any changes to the last few lines of the file.
"watch -n 5 tail -n 15 logfile.txt" will grab last 15 lines of "logfile.txt" and will watch them every 5 seconds.
Moving and copying files:
to move file we use: "mv source_filename /directory/destination_filename"
same is for copying files: "cp filename /directory/"
We can delete files using: "rm file_name" or just all files within a directory with "rm *"
Permissions
When we run: ls -la we see bunch of information about the objects within a directory. For example:
-rwxr-xr-x 1 nevyan nevyan 4096 nov 25 20:34 file
drwxr-xr-x 2 nevyan nevyan 4096 nov 25 20:34 Public
Lets start with the first row representing a file. We know it is a file because the first character of the first column doesn't start with D.
Then we can see its permissions: They are divided into groups of 3(rwx). (read, write and execute)
First 1 group are for the owner(creator) of the file, then for the group it belongs, and last ones are for every other user.
We use groups in order to be able to set once permissions for multiple users belonging to a group, so they can automatically get those permissions.
For example:
just to be able to "cd" into a directory we need to have (+x) execute rights over the directory.
to be able to list file contents with cat we need (+r)read rights over the file.
Linux applies the principle of least privileges, which means that a user is given not more than the privileges he/she needs for completing a certain task. Let's now take a look of what is inside of /etc/shadow with the cat command. We will see: 13 permission denied
Reason is that only the root user can read this file. You can check this out by issuing: ls -la /etc/shadow and look at the others group(3rd) we see - which means no one else except its owner have rights over this file. And the owner can be seen on the second column (root).
If we run the same command, appending "sudo" in front:
"sudo ls -la /etc/shadow"
(and type the root password)
we will see that we have rights to look at the file. This is because for this particular command we have gained temporary "root" rights
Next we can take a look at /etc/passwd - there we can see all the users registered into the server, their login names, hidden password, user id, group, home directory as well as working shell(command prompt).
Changing permissions:
"chmod ugo+rwx file_name.txt"
this will give maximum privileges(rwx) to all(user,group and others) to file_name.txt
Changing ownership:
to change the ownership we can type:
"chown user1:user1 file_name.txt"
will set user=user1 and group=user1 to the file.
Groups:
Each user can belong to one primary and several secondary groups.
"id" shows the current groups our user belongs to. We can issue: groups and user_name to find out which groups specific user belongs to:
"groups user_name" will list the information in format: (primary, secondary) groups
The same information can be gained from the file: "/etc/group" and we can list information about particular group with: "cat /etc/group | grep mygroup"
"addgroup mygroup" will add new "mygroup" to our currenly existing groups
"usermod -G mygroup nevyan" will remove all secondary groups and will add secondary group "mygroup" to user "nevyan"
With the flag -g we can change the user primary group and if we want just to append another secondary group to our user we can use the -aG flag.
In order to remove user from a group: "deluser nevyan mygroup"
and finally to remove a group we do: "sudo delgroup mygroup"
Notice that we need to "logout" in order to see the effect of those group changes.
Congratulations and enjoy the ubuntu linux server course:
Our journey into SEO starts with the terms of crawling and indexing. So let’s point out the main differences between them.
For more information, you can take a look at my search engine optimization course
In order for a specific URL to show up, when searching in Google’s index it has to be discovered. This is the main purpose of the crawling process. So when a particular web site is being submitted to Google for indexing the crawler first fetches its main entry point which is usually index.html file and then it tries to discover as much as possible internal pages following the web page links. Next for each discovered page the crawler makes an HTTP request just like you do in a browser and parses all the found content so it can gather readable information.
The process of parsing includes: removing all the HTML tags, scripts, styles and the so-called “stop words”. Stop words usually represent commonly used words and just because they bring noise to the information they are being discarded. After the cleanup, algorithms of machine learning are trying to understand the topic of the content based on information they have learned from previous websites. You may ask yourself what does the Google index look like?
Although the real index and all the factors which Google takes into account before ranking a web page for a specific keyword remain a secret. We could represent the index as a table-like distributed database structure which holds the following columns: term or keyword and path to a document (from the website documents) where the keyword is found. In other words, this table is used to map the relevance of the keyword towards a particular web document, so in a case of search, the search engine could easily determine where (in which document) a specific word could be found.Now that we have a grasp on the index structure let’s take a look at the actual process of Indexing: The search engine performs two main tasks: first is to find meaningful words from the parsed content related to its topic and the second is to associate them together with the path to the document in its existing index. You may ask how the engine knows if a particular keyword is relevant? The local relevancy of a word or a combination of words for a particular document is calculated using techniques such as Inverted index, Latent Semantic Indexing, and others:
The Inverted index is a data structure where all the unique words found in a document are mapped to a list of documentswhere they also appear.
In LSI the mapping additionally considers relations between keywords and concepts contained in a collection of text documents.
When a meaningful keyword is found, it is then linked to its source document or multiple documents forming a new data entry in the table structure. Now the second step of the indexing process is when the search engine tries to fit the data entry within the existing index. The comparison process takes into account more than 200 factors that feed Machine Learning algorithms. Additionally, human evaluators are being used to determine the relevancy of a particular keyword for a particular document.
One more thing: in this process, you have to know that all the cached copies of the documents are archived and stored in another place.
Crawling and indexing continued
There are ways to control the crawler’s access to a website as well as to choose which pages to be taken into account for indexing. This can be done by placing a meta tag in the head section of a particular web page as well as by creating and using a robots.txt file inside the website’s root directory.
There are two properties: index and follow which are related to indexing and crawling processes that we will discuss:
Meta: index says that the page should be added to the index database.
Meta: follow controls crawling of the inner links inside the web page.
If we would like to restrict the crawler’s access to content we would use “nofollow” attribute.
If we would like the web page not to be a part of the search engine index, and to be excluded from the search results we use the “noindex” attribute.
The robots.txt file is primarily used for excluding crawling of a web page. It is a text file containing information on which pages/domains/directories to be included/or excluded from a particular website. It is one per website and resides in its root directory.
Robots.txt example:
Now let's see the difference between using robots.txt and meta tags with an example of crawl blocking.
The next example is showing how we can have a website but some of its web pages to continue displaying: A description for this result is not available because of this site’s robots.txt file.
First, let's discuss why we are having this situation. Apparently, this website has in its description the tag: meta robots=”index” so it has been indexing appropriately,
but in the robots.txt file we have disallowed this web page, so it's denying the display of the description of the result. In this way, the web page is added to the index (have been discovered), but has not being crawled (link index)
Before proceeding with the next examples, lets first be clear on what is link juice?
It is actually the value passed from one page or site to another through hyperlinks. Search engines see it as a vote or a signal by other pages that the page they are linking to is valuable.
In the figure on the left side, you can see how one page can pass link juice to another.
We will discuss the other four cases which prevent the flow of link juice:
If the main page returns 404 or not found, its link juice will not be calculated and transferred to the other page.
If the page we are linking to cannot be found also the link juice remains in the source page
For the next two cases, we have to see what does ...robots.txt file example photo
do. It is a plain text document file, where we can describe directories and files to be allowed or disallowed from crawling when a particular search engine visits our website.
When a page is disallowed in the robots.txt file its internal links would not be passing link juice to the destination page
And finally, if a page has a “nofollow” attribute placed on the link, the link will not flow it to the destination page.
Penguin update
This update main goal is to prevent the exchange of bad linking practices between websites. Such schemes are used by SEO 'specialists' in order to increase a particular website reputation. As well as in reverse direction, to negatively affect specific website by having lots of low-quality website links pointing to the targeted website. Here is how to clean up such situations. We can go to the search console and from there to see who is linking to us. Then we check all the listed domains by hand for issues. Other free websites that are also very helpful for finding back-linking sites are NeilPatel's website as well as backlinkwatch. After obtaining the spammy websites list we just create a plain text file disavow.txt where we place all the links following the format: domain: spammy.com. The last step is to upload the file to google's disavow tool. You will have to wait some days before the penalty imposed by this kind of negative SEO will be released.
Panda/topical/quality update
This penalty affects the entire website and even a single webpage could cause it.
Here are a few ways on how to remedy the situation if your website is being targeted by the Panda update:
If you have very similar articles just merge them or add more relevant content to the shorter ones. For articles aim for having about 1000 words of content.
In order to identify what might be the source of the problem, especially if you have lots of pages, you can group your categories into subdomains. Then the search console, will allow you to inspect them by domain so you can gain insight into which categories perform better and decide whether to correct the weak pages or just disallow the whole category. You can become even more granular by using sitemaps of the whole site pages. After submitting the sitemap in search console, you will have information on which pages are being fully indexed and which are having problems. The benefit of this technique is that it will show you which categories are not performing well to the level of individual URLs.
In case you have an article which spans in multiple pages, you can add rel next and rel prev inside your HTML markup, so Google can treat those pages as a group of pages.
More techniques:
First, identify the top 5 pages receiving most impressions and at the same time having very low CTR (clicks). The improvement action in such a case for you is just to correct their meta description and title in order to help them become more attractive to the visitors.
Transfer power from higher to lower-ranking pages, or just analyze the good rank pages and how they differ from the lower-ranking pages. When done you can either delete the weak pages or merge them into the powerful pages.
For comments: choose to be displayed only after a user performs an action such as clicking on a button. On one hand this improves the UI and on other it prevents SPAM. In many cases webmasters choose just to disallow commenting on pages altogether.
The most effective yet longest technique for dealing with the Panda update is to allow only high-quality pages inside the Google index. Start with a few ones which already have good click-through rate and impressions, and then gradually allow more pages to the quality indexed list by rewriting, updating or adding new information inside.
Top-heavy update
The update targets websites that use too much of an advertisement inside the first screen a particular user sees. This way you might have great content, but if it is being occupied with advertisement the penalty will be triggered.
The suggestions in such cases are to have only: 1 ad above the fold (before reaching the vertical scroll height), and it should be of less than 300x250px and 1 per page (for mobile devices). The alternative is to use the auto ad placement available from Google Adsense.
Windows 7
Negative Screen
https://zerowidthjoiner.net/Uploads/negativescreen/Binary.zip Windows 10
there is already present grayscale mode: from the Turn color filters on or off
Gnome:
install an extension called: Desaturate_all Note: to run the script successfully just comment the two lines:
// x_fill: true,
// y_fill: false, inside extension.js
https://extensions.gnome.org/
KDE:
https://github.com/ugjka/kwin-effect-grayscale
Ubuntu/Debian:
install: sudo apt install kwin-dev libkf5xmlgui-dev libkf5service-dev libkf5globalaccel-dev libkf5configwidgets-dev qt5-default
git clone https://github.com/ugjka/kwin-effect-grayscale.git cd kwin-effect-grayscale mkdir build && cd build cmake .. -DCMAKE_C_FLAGS:STRING="" -DCMAKE_CXX_FLAGS:STRING="" -DCMAKE_EXE_LINKER_FLAGS:STRING="" -DCMAKE_SHARED_LINKER_FLAGS:STRING="" -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib make sudo make install
Then enable the grayscale color filter from Desktop Effects menu
LxQt:
create a filter file: grayscale.glsl with the following contents:
uniform float opacity; uniform bool invert_color; uniform sampler2D tex;
void main() { vec4 c = texture2D(tex, gl_TexCoord[0].xy); float y = dot(c.rgb, vec3(0.299, 0.587, 0.114)); // y = 1.0 -y; gl_FragColor = vec4(y, y, y, 1.0); }
then just apply the filter with:
compton --backend glx --glx-fshader-win "$(cat ./grayscale.glsl)"
Please enjoy a less distractive / addictive world.
