Docker – Ubuntu – bash: ping: command not found

Docker images are pretty minimal, But you can install ping in your official ubuntu docker image via:

apt-get update
apt-get install iputils-ping

Chances are you dont need ping your image, and just want to use it for testing purposes. Above example will help you out.

But if you need ping to exist on your image, you can create a Dockerfile or commit the container you ran the above commands in to a new image.


docker commit -m "Installed iputils-ping" --author "Your Name <>" ContainerNameOrId yourrepository/imagename:tag


FROM ubuntu
RUN apt-get update && apt-get install -y iputils-ping
CMD bash

PAE – Physical Address Extension

In computingPhysical Address Extension (PAE), sometimes referred to as Page Address Extension, is a memory management feature for the x86 architecture. PAE was first introduced by Intel in the Pentium Pro, and later by AMD in the Athlon processor. It defines a page table hierarchy of three levels (instead of two), with table entries of 64 bits each instead of 32, allowing these CPUs to directly access a physical address space larger than 4 gigabytes (232 bytes).

The page table structure used by x86-64 CPUs when operating in long mode further extends the page table hierarchy to four levels, extending the virtual address space, and uses additional physical address bits at all levels of the page table, extending the physical address space. It also uses the topmost bit of the 64-bit page table entry as a no-execute or “NX” bit, indicating that code cannot be executed from the associated page. The NX feature is also available in protected mode when these CPUs are running a 32-bit operating system, provided that the operating system enables PAE.

(PAE) stand for Physical Address Extension. It’s a feature of x86 and x86-64 processors that allows more than 4 Gigabytes of physical memory to be used in 32-bit systems.

Without PAE kernel, you should see something as follows:

free -m

Sample output:

enter image description here

To enable PAE, open terminal and type the following command:

sudo apt-get install linux-headers-server linux-image-server linux-server

Reboot your machine.

Now check again :

free -m

Sample output:

enter image description here

pyDash – A Web Based Linux Performance Monitoring Tool

pydash is a lightweight web-based monitoring tool for Linux written in Python and Django plus Chart.js. It has been tested and can run on the following mainstream Linux distributions: CentOS, Fedora, Ubuntu, Debian, Arch Linux, Raspbian as well as Pidora.

You can use it to keep an eye on your Linux PC/server resources such as CPUs, RAM, network stats, processes including online users and more. The dashboard is developed entirely using Python libraries provided in the main Python distribution, therefore it has a few dependencies; you don’t need to install many packages or libraries to run it.

In this article, we will show you how to install pydash to monitor Linux server performance.

How to Install pyDash in Linux System

1. First install required packages: git and Python pip as follows:

-------------- On Debian/Ubuntu -------------- 
$ sudo apt-get install git python-pip
-------------- On CentOS/RHEL -------------- 
# yum install epel-release
# yum install git python-pip
-------------- On Fedora 22+ --------------
# dnf install git python-pip

2. If you have git and Python pip installed, next, install virtualenv which helps to deal with dependency issues for Python projects, as below:

# pip install virtualenv
$ sudo pip install virtualenv

3. Now using git command, clone the pydash directory into your home directory like so:

# git clone
# cd pydash

4. Next, create a virtual environment for your project called pydashtest using the virtualenv command below.

$ virtualenv pydashtest #give a name for your virtual environment like pydashtest

Create Virtual Environment

Important: Take note the virtual environment’s bin directory path highlighted in the screenshot above, yours could be different depending on where you cloned the pydash folder.

5. Once you have created the virtual environment (pydashtest), you must activate it before using it as follows.

$ source /home/aaronkilik/pydash/pydashtest/bin/activate

Active Virtual Environment

From the screenshot above, you’ll note that the PS1 prompt changes indicating that your virtual environment has been activated and is ready for use.

6. Now install the pydash project requirements; if you are curious enough, view the contents of requirements.txt using the cat command and the install them using as shown below.

$ cat requirements.txt
$ pip install -r requirements.txt

7. Now move into the pydash directory containing or simple run the command below to open this file to change the SECRET_KEY to a custom value.

$ vi pydash/

Set Secret Key

Save the file and exit.

8. Afterward, run the django command below to create the project database and install Django’s auth system and create a project super user.

$ python syncdb

Answer the questions below according to your scenario:

Would you like to create one now? (yes/no): yes
Username (leave blank to use 'root'): admin
Email address:
Password: ###########
Password (again): ############

Create Project Database

9. At this point, all should be set, now run the following command to start the Django development server.

$ python runserver

10. Next, open your web browser and type the URL: to get the web dashboard login interface. Enter the super user name and password you created while creating the database and installing Django’s auth system in step 8 and click Sign In.

pyDash Login Interface

11. Once you login into pydash main interface, you will get a section for monitoring general system info, CPU, memory and disk usage together with system load average.

Simply scroll down to view more sections.

pyDash Server Performance Overview

12. Next, screenshot of the pydash showing a section for keeping track of interfaces, IP addresses, Internet traffic, disk read/writes, online users and netstats.

pyDash Network Overview

13. Next is a screenshot of the pydash main interface showing a section to keep an eye on active processes on the system.

pyDash Active Linux Processes

fswatch – Monitors Files and Directory Changes or Modifications in Linux

fswatch is a cross-platform, file change monitor that gets notification alerts when the contents of the specified files or directories are altered or modified.

It executes four types of monitors on different operating systems such as:

  1. A monitor build on the File System Events API of Apple OS X.
  2. A monitor based on kqueue, a notification interface present in FreeBSD 4.1 also supported on many *BSD systems, OS X inclusive.
  3. A monitor based on File Events Notification API of the Solaris kernel plus its spin-offs.
  4. A monitor based on inotify, a kernel subsystem that shows file system modifications to apps.
  5. A monitor based on ReadDirectoryChangesW, a Windows API that records alters to a directory.
  6. A monitor that regularly check that status of file system, keeps file modification times in memory, and manually determine file system changes (which works anywhere, where stat can be used).

Features of fswatch

  1. Supports several OS-specific APIs
  2. Allows recursive directory monitoring
  3. Performs path filtering using including and excluding regular expressions
  4. Supports customizable record format
  5. Additionally, it supports periodic idle events

How To Install fswatch in Linux Systems

Unfortunately, fswatch package is not available to install from the default system repositories in any Linux distributions. The only way to install the latest version of fswatch is to build from source tarball as show in the following installation instructions.

First grab the latest fswatch tarball using following wget command and install it as shown:

$ wget
$ tar -xvzf fswatch-1.9.3.tar.gz
$ cd fswatch-1.9.3
$ ./configure
$ make
$ sudo make install 

Important: Make sure you’ve GNU GCC (C and C++ Compiler) and Development Tools (build-essential on Debian/Ubuntu) installed on the system, before you compile fswatch from source. If not, install it using following command on your respective Linux distributions..

# yum group install 'Development Tools'		[On CentOS/RHEL]
# dnf group install 'Development Tools'		[On Fedora 22+ Versions]
$ sudo apt-get install build-essential          [On Debian/Ubuntu Versions]

On Debian/Ubuntu distributions, you might get following error while executing fswatch command..

fswatch: error while loading shared libraries: cannot open shared object file: No such file or directory

To fix it, you need to execute the command below, this will help refresh the links and cache to the dynamic libraries before you can start using fswatch.

$ sudo ldconfig

How do I use fswatch on Linux?

The general syntax for running fswatch is:

$ fswatch [option] [path]

On Linux, it is recommended that you use the default inotify monitor, you can list available monitors by employing the -M or - list-monitors option:

$ fswatch -M
$ fswatch --list-monitors

fswatch - List Monitors

The command below enables you to watch the changes in the current directory (/home/tecmint), with events being delivered to standard output every 4 seconds.

The -l or –-latency option allows you to set the latency in seconds, the default being 1 second.

$ fswatch -l 4 .

fswatch - Monitor Home Directory Changes

The next command monitors changes to the /var/log/auth.log file every 5 seconds:

$ fswatch -l 5 /var/log/auth.log

Using -t or --timestamp option prints the time stamp for every event, to print the time in UTC format, employ -u or --utf-time option. You can as well format time using -f or --format-time format option:

$ fswatch --timestamp /var/log/auth.log

Next, -x or --event-flags tells fswatch to print the event flags along side the event path. You can use –event-field-seperator option to print events using the particular separator.

$ fswatch --events-flags ~ /var/log/auth.log

To print the numeric value of an event indicating changes in your home directory and /var/log/auth.log file, use -n or --numeric option as below:

$ fswatch --numeric ~ /var/log/auth.log 

Perhaps you can look through the fswatch man page for detailed usage options and information:

$ man fswatch

How to List Files Installed From a RPM or DEB Package in Linux

Have you ever wondered where the various files contained inside a package are installed (located) in the Linux file system? In this article, we’ll show how to list all files installed from or present in a certain package or group of packages in Linux.

This can help you to easily locate important package files like configurations files, documentation and more. Let’s look at the different methods of listing files in or installed from a package:

How to List All Files of Installed Package in Linux

You can use the repoquery command which is part of the yum-utils to list files installed on a CentOS/RHEL system from a given package.

To install and use yum-utils, run the commands below:

# yum update 
# yum install yum-utils

Now you can list files of an installed RPM package, for example httpd web server (note that the package name is case-sensitive). The --installed flag means installed packages and -l flags enables listing of files:

# repoquery --installed -l httpd
# dnf repoquery --installed -l httpd  [On Fedora 22+ versions]

Repoquery List Installed Files of Httpd

Important: In Fedora 22+ version, the repoquery command is integrated with dnf package manager for RPM based distribution to list files installed from a package as shown above.

Alternatively, you can as well use the rpm command below to list the files inside or installed on the system from a .rpm package as follows, where the -g and -l means to list files in package receptively:

# rpm -ql httpd

RPM Query Package for Installed Files

Another useful option is used to use -p to list .rpm package files before installing it.

# rpm -qlp telnet-server-1.2-137.1.i586.rpm

On Debian/Ubuntu distributions, you can use the dpkg command with the -L flag to list files installed to your Debian system or its derivatives, from a given .deb package.

In this example, we will list files installed from apache2 web server:

$ dpkg -L apache2

dpkg List Installed Packages

All You Need To Know About Processes in Linux

In this article, we will walk through a basic understanding of processes and briefly look at how to manage processes in Linux using certain commands.

A process refers to a program in execution; it’s a running instance of a program. It is made up of the program instruction, data read from files, other programs or input from a system user.

Types of Processes

There are fundamentally two types of processes in Linux:

  • Foreground processes (also referred to as interactive processes) – these are initialized and controlled through a terminal session. In other words, there has to be a user connected to the system to start such processes; they haven’t started automatically as part of the system functions/services.
  • Background processes (also referred to as non-interactive/automatic processes) – are processes not connected to a terminal; they don’t expect any user input.

What is Daemons

These are special types of background processes that start at system startup and keep running forever as a service; they don’t die. They are started as system tasks (run as services), spontaneously. However, they can be controlled by a user via the init process.

Linux Process State

Creation of a Processes in Linux

A new process is normally created when an existing process makes an exact copy of itself in memory. The child process will have the same environment as its parent, but only the process ID number is different.

There are two conventional ways used for creating a new process in Linux:

  • Using The System() Function – this method is relatively simple, however, it’s inefficient and has significantly certain security risks.
  • Using fork() and exec() Function – this technique is a little advanced but offers greater flexibility, speed, together with security.

How Does Linux Identify Processes?

Because Linux is a multi-user system, meaning different users can be running various programs on the system, each running instance of a program must be identified uniquely by the kernel.

And a program is identified by its process ID (PID) as well as it’s parent processes ID (PPID), therefore processes can further be categorized into:

  • Parent processes – these are processes that create other processes during run-time.
  • Child processes – these processes are created by other processes during run-time.

The Init Process

Init process is the mother (parent) of all processes on the system, it’s the first program that is executed when the Linux system boots up; it manages all other processes on the system. It is started by the kernel itself, so in principle it does not have a parent process.

The init process always has process ID of 1. It functions as an adoptive parent for all orphaned processes.

You can use the pidof command to find the ID of a process:

# pidof systemd
# pidof top
# pidof httpd

Find Linux Process ID

To find the process ID and parent process ID of the current shell, run:

$ echo $$
$ echo $PPID

Find Linux Parent Process ID

Starting a Process in Linux

Once you run a command or program (for example cloudcmd – CloudCommander), it will start a process in the system. You can start a foreground (interactive) process as follows, it will be connected to the terminal and a user can send input it:

# cloudcmd

Start Linux Interactive Process

Linux Background Jobs

To start a process in the background (non-interactive), use the & symbol, here, the process doesn’t read input from a user until it’s moved to the foreground.

# cloudcmd &
# jobs

Start Linux Process in Background

You can also send a process to the background by suspending it using [Ctrl + Z], this will send the SIGSTOP signal to the process, thus stopping its operations; it becomes idle:

# tar -cf backup.tar /backups/*  #press Ctrl+Z
# jobs

To continue running the above-suspended command in the background, use the bg command:

# bg

To send a background process to the foreground, use the fg command together with the job ID like so:

# jobs
# fg %1

Linux Background Process Jobs

You may also like: How to Start Linux Command in Background and Detach Process in Terminal

States of a Process in Linux

During execution, a process changes from one state to another depending on its environment/circumstances. In Linux, a process has the following possible states:

  • Running – here it’s either running (it is the current process in the system) or it’s ready to run (it’s waiting to be assigned to one of the CPUs).
  • Waiting – in this state, a process is waiting for an event to occur or for a system resource. Additionally, the kernel also differentiates between two types of waiting processes; interruptible waiting processes – can be interrupted by signals and uninterruptible waiting processes – are waiting directly on hardware conditions and cannot be interrupted by any event/signal.
  • Stopped – in this state, a process has been stopped, usually by receiving a signal. For instance, a process that is being debugged.
  • Zombie – here, a process is dead, it has been halted but it’s still has a task to perform on the system.

How to View Active Processes in Linux

There are several Linux tools for viewing/listing running processes on the system, the two traditional and well known are ps and top commands:

1. ps Command

It displays information about a selection of the active processes on the system as shown below:

# ps 
# ps -e | head 

List Linux Active Processes

2. top – System Monitoring Tool

top is a powerful tool that offers you a dynamic real-time view of a running system as shown in the screenshot below:

# top 

Read this for more top usage examples: 12 TOP Command Examples in Linux

3. glances – System Monitoring Tool

glances is a relatively new system monitoring tool with advanced features:

# glances

For a comprehensive usage guide, read through: Glances – An Advanced Real Time System Monitoring Tool for Linux

There are several other useful Linux system monitoring tools you can use to list active processes, open the link below to read more about them:

  1. 20 Command Line Tools to Monitor Linux Performance
  2. 13 More Useful Linux Monitoring Tools

How to Control Processes in Linux

Linux also has some commands for controlling processes such as kill, pkill, pgrep and killall, below are a few basic examples of how to use them:

$ pgrep -u tecmint top
$ kill 2308
$ pgrep -u tecmint top
$ pgrep -u tecmint glances
$ pkill glances
$ pgrep -u tecmint glances

Control Linux Processes

To learn how to use these commands in-depth, to kill/terminate active processes in Linux, open the links below:

  1. A Guide to Kill, Pkill and Killall Commands to Terminate Linux Processess
  2. How to Find and Kill Running Processes in Linux

Note that you can use them to kill unresponsive applications in Linux when your system freezes.

Sending Signals To Processes

The fundamental way of controlling processes in Linux is by sending signals to them. There are multiple signals that you can send to a process, to view all the signals run:

$ kill -l

List All Linux Signals

To send a signal to a process, use the kill, pkill or pgrep commands we mentioned earlier on. But programs can only respond to signals if they are programmed to recognize those signals.

And most signals are for internal use by the system, or for programmers when they write code. The following are signals which are useful to a system user:

  • SIGHUP 1 – sent to a process when its controlling terminal is closed.
  • SIGINT 2 – sent to a process by its controlling terminal when a user interrupts the process by pressing [Ctrl+C].
  • SIGQUIT 3 – sent to a process if the user sends a quit signal [Ctrl+D].
  • SIGKILL 9 – this signal immediately terminates (kills) a process and the process will not perform any clean-up operations.
  • SIGTERM 15 – this a program termination signal (kill will send this by default).
  • SIGTSTP 20 – sent to a process by its controlling terminal to request it to stop (terminal stop); initiated by the user pressing [Ctrl+Z].

The following are kill commands examples to kill the Firefox application using its PID once it freezes:

$ pidof firefox
$ kill 9 2687
$ kill -KILL 2687
$ kill -SIGKILL 2687  

To kill an application using its name, use pkill or killall like so:

$ pkill firefox
$ killall firefox 

Changing Linux Process Priority

On the Linux system, all active processes have a priority and certain nice value. Processes with higher priority will normally get more CPU time than lower priority processes.

However, a system user with root privileges can influence this with the nice and renice commands.

From the output of the top command, the NI shows the process nice value:

$ top  

List Linux Running Processes

Use the nice command to set a nice value for a process. Keep in mind that normal users can attribute a nice value from zero to 20 to processes they own.
Only the root user can use negative nice values.

To renice the priority of a process, use the renice command as follows:

$ renice +8  2687
$ renice +8  2103




Checksum is like a digital fingerprint of a file. In technical terms,

A checksum is a small-sized datum from a block of digital data for the purpose of detecting errors which may have been introduced during its transmission or storage.

Well, checksum is a long string of data containing various letters and numbers. You’ll generally find them while downloading files from the web, e.g. Linux distribution image, software packages etc.

Most common use of checksum is in checking if the downloaded file is corrupted.

For instance, Ubuntu MATE download page includes SHA256 checksum for every image available there. So, after you downloaded an image, you can generate SHA256 checksum for it and verify if the checksum value matches the one mentioned on the site.

If it doesn’t, that will mean your downloaded image’s integrity is compromised (maybe it was corrupted during the download process). We will use Ubuntu Mate “ubuntu-mate-16.10-desktop-amd64.iso” image file for this guide.


Checksum is generated by checksum algorithm. Without going into technical details let’s say that it takes a file as input and outputs the checksum value of that file. There are various algorithms for generating checksum. Most popular checksum algorithms are:

  • Secure Hash Algorithms and variants (SHA-1, SHA-2 etc.) and
  • MD5 Algorithm


If you are looking for graphical solution, you can use GtkHash.

GtkHash is a nifty tool for generating and verifying various checksums. It supports a wide range of checksum algorithms – including SHA, MD5 and others. Here’s a list of supported algorithms:

GtkHash supported Checksum Algorithms


For installing GtkHash on your Ubuntu system, simply run the following command:

sudo apt install gtkhash

That’s it.

GtkHash with UbuntuMATE iso


Every Linux distribution comes with tools for various checksum algorithms. You can generate and verify checksum with them. The command-line checksum tools are the followings:

  • MD5 checksum tool is called: md5sum
  • SHA-1 checksum tool is called: sha1sum
  • SHA-256 checksum tool is called: sha256sum

There are some more available, e.g.: sha224sum, sha384sum etc. All of them uses similar command formats. Let’s see an example of using sha256sum. We will use the same “ubuntu-mate-16.10-desktop-amd64.iso” image file as we used before.


First go to the directory where the .iso image is stored:

cd ~/itsfoss

Now, for generating SHA256 checksum, enter the following command:

sha256sum ubuntu-mate-16.10-desktop-amd64.iso

You will get the SHA256 checksum in your terminal window! Easy, isn’t it?

Generating SHA256 Checksum for UbuntuMATE iso

If the generated checksum matches with the one provided on the UbuntuMATE download page, that will mean – no data was changed while you downloaded the file or putting otherwise, your downloaded file is not corrupted.

The other mentioned tools work similarly.


If you are wondering, how accurately does these checksum detects corrupted files – if you delete or change even one character from any one of the text files inside the iso image, the checksum algorithm will generate a totally different checksum value for that changed iso image. And that will definitely not match with the checksum provided on the download page.