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As a system administrator, you may have a certain directory that you want to give read/write access to every user on a Linux server. In this guide, we will review how to enable write access to all users on a particular directory (shared directory) in Linux.

This calls for setting the appropriate access permissions, and the most effective as well as reliable method to allocating a common group for all the users who will share or have write access to the specific directory.

So, start by creating the directory and common group in case it doesn’t already exist on the system as follows:

$ sudo mkdir -p /var/www/reports/
$ sudo groupadd project 

Then add an existing user who will have write access to the directory: /var/www/reports/ to the group project as below.

$ sudo usermod -a -G project tecmint 

$ sudo chgrp -R project /var/www/reports/
$ sudo chmod -R 2775 /var/www/reports/

$ sudo useradd -m -c "Aaron Kili" -s/bin/bash -G project aaronkilik
$ sudo useradd -m -c "John Doo" -s/bin/bash -G project john
$ sudo useradd -m -c "Ravi Saive" -s/bin/bash -G project ravi

$ sudo mkdir -p /var/www/reports/aaronkilik_reports
$ sudo mkdir -p /var/www/reports/johndoo_reports
$ sudo mkdir -p /var/www/reports/ravi_reports

Sometimes it may happens in some stage, you may have to access data on a Windows partition, USB device or any similar device. Today most of the modern Linux systems automatically recognize and mount any disks.

However, in some occasions where you may required to configure your system manually to mount ntfs partitions on your Linux system. Specially when you are using dual boot operating environment. Fortunately, this process is not so complicated task its just very fairly straight forward.

This article explains you on how to access or mount Windows XP, Vista NTFS or USB filesystem using the ‘mount‘ command in RHEL/CentOS/Fedora systems.

How to Mount Windows NTFS Partition in Linux

First you need to enable EPEL (Extra Packages for Enterprise Linux) Repository. You may refer the article on how to enable EPEL Repository under RHEL, CentOS and Fedora systems.

To mount any NTFS based filesystem, you need to install a tool called NTFS3G. Before heading up for installation let’s understand NTGS3G.

What is NTFS3G

NTFS3G is an open source cross-platform, stable, GPL licensed, POSIX, NTFS R/W driver used in Linux. It provides safe handling of Windows NTFS file systems viz create, remove, rename, move files, directories, hard links, etc.

Once EPEL is installed and enabled, let’s install ntfs-3g package using the below command with root user.

# yum -y install ntfs-3g

Fuse Install

Next, install and load FUSE driver to mount detected devices with below command. FUSE module is included in the kernel itself in version 2.6.18-164 or newer.

# yum install fuse
# modprobe fuse

Identify NTFS Partition

Once fuse module is loaded, type below command to find out NTFS Partitions in Linux.

# fdisk -l

 Device Boot      Start    End      Blocks   Id  System
/dev/sdb1         1	   21270    7816688   b  W95 FAT32

Mount NTFS partition

First create a mount point to mount the NTFS partition.

# mkdir /mnt/nts

Simply run the following command to mount the partition. Replace sda1 with your actual partition found.

# mount -t ntfs-3g /dev/sda1 /mnt/nts

Once it’s mounted on /mnt/ntfs, you may use regular Linux ls -l command to list the content of mounted filesystem.

[root@tecmint ntfs]# ls -l
total 27328
drwx------.  2 root root    16384 Sep  2 19:37 Cert
drwx------. 20 root root    16384 Aug 24  2011 club_application
drwx------.  6 root root    16384 Aug 11 15:37 docs
drwx------.  7 root root    16384 Jul 31  2012 Downloads
drwx------.  2 root root    16384 Dec 10 20:28 images
-rwxr-xr-x.  1 root root    31744 Jan 18 00:29 Material List.doc

If you want to make mount point permanent at the boot time, then simple add the following line at the end of /etc/fstab file. This will remain as permanent.

/dev/sda1    /mnt/usb    ntfs-3g        defaults    0    0

Umount NTFS Partition

Simply, use the following command to unmount the mounted partition.

# umount /mnt/usb

Read Also : How to Mount ISO Images in Linux

Source

The root account is the ultimate account on a Linux and other Unix-like operating systems. This account has access to all commands and files on a system with full read, write and execute permissions. It is used to perform any kind of task on a system; to create/update/access/delete other users’ accounts, install/remove/upgrade software packages, and so much more.

Because the root user has absolute powers, any actions he/she performs are critical on a system. In this regard, any errors by the root user may have huge implications on the normal operation of a system. In addition, this account may also be abused by using it improperly or inappropriately either accidentally, maliciously, or through contrived ignorance of policies.

Therefore, it is advisable to disable the root access in your Linux server, instead, create an administrative account which should be configured to gain root user privileges using the sudo command, to perform critical tasks on the server.

In this article, we will explain four ways to disable root user account login in Linux.

Attention: Before you block access to the root account, make sure you have created an administrative account, capable of using sudo command to gain root user privileges, with the useradd command and give this user account a strong password. The flag -m means create user’s home directory and -c allows to specify a comment:

# useradd -m -c "Admin User" admin
# passwd admin

Next, add this user to the appropriate group of system administrators using the usermod command, where the switch -a means append user account and -G specifies a group to add the user in (wheel or sudo depending on your Linux distribution):

# usermod -aG wheel admin    #CentOS/RHEL
# usermod -aG sudo admin     #Debian/Ubuntu 

Once you have created a user with administrative privileges, switch to that account in order to block root access.

# su admin

1. Change root User’s Shell

The simplest method to disable root user login is to change its shell from /bin/bash or /bin/bash (or any other shell that permits user login) to /sbin/nologin, in the /etc/passwd file, which you can open for editing using any of your favorite command line editors as shown.

  
$ sudo vim /etc/passwd

Change the line:

root:x:0:0:root:/root:/bin/bash
to
root:x:0:0:root:/root:/sbin/nologin

Save the file and close it.

From now on, when root user logs in, he/she will get the message “This account is currently not available.” This is the default message, but, you can change it and set a custom message in the the file /etc/nologin.txt.

This method is only effective with programs that require a shell for user login, otherwise, sudo, ftp and emailclients can access the root account.

2. Disable root Login via Console Device (TTY)

The second method uses a PAM module called pam_securetty, which permits root access only if the user is logging in on a “secure” TTY, as defined by the listing in /etc/securetty.

The above file allows you to specify which TTY devices the root user is allowed to login on, emptying this file prevents root login on any devices attached to the computer system.

To create an empty file, run.

$ sudo mv /etc/securetty /etc/securetty.orig
$ sudo touch /etc/securetty
$ sudo chmod 600 /etc/securetty

This method has some limitations, it only affects programs such as login, display managers (i.e gdm, kdm and xdm) and other network services that launch a TTY. Programs such as su, sudo, ssh, and other related openssh tools will have access to the root account.

3. Disabl SSH Root Login

The commonest way of accessing remote servers or VPSs is via SSH and to block root user login under it, you need to edit the /etc/ssh/sshd_config file.

$ sudo vim /etc/ssh/sshd_config

Then uncomment (if it is commented) the directive PermitRootLogin and set its value to no as shown in the screenshot.

Once you are done, save and close the file. Then restart the sshd service to apply the recent change in configurations.

$ sudo systemctl restart sshd 
OR
$ sudo service sshd restart 

As you may already know, this method only affects openssh tools set, programs such as ssh, scp, sftp will be blocked from accessing the root account.

4. Restrict root Acess to Services Via PAM

Pluggable Authentication Modules (PAM in short) is a centralized, pluggable, modular, and flexible method of authentication on Linux systems. PAM, through the /lib/security/pam_listfile.so module, allows great flexibility in limiting the privileges of specific accounts.

The above module can be used to reference a list of users who are not allowed to log in via some target services such as login, ssh and any PAM aware programs.

In this case, we want to disable root user access to a system, by restricting access to login and sshd services. First open and edit the file for the target service in the /etc/pam.d/ directory as shown.

$ sudo vim /etc/pam.d/login
OR
sudo vim /etc/pam.d/sshd

Next, add the configuration below in both files.

auth    required       pam_listfile.so \
        onerr=succeed  item=user  sense=deny  file=/etc/ssh/deniedusers

When you are done, save and close each file. Then create the plain file /etc/ssh/deniedusers which should contain one item per line and not world readable.

Add the name root in it, then save and close it.

$ sudo vim /etc/ssh/deniedusers

Also set the required permissions on this.

$ sudo chmod 600 /etc/ssh/deniedusers

This method only affect programs and services that are PAM aware. You can block root access to the system via ftp and email clients and more.

For more information, consult the relevant man pages.

$ man pam_securetty
$ man sshd_config
$ man pam

That’s all! In this article, we have explained four ways of disabling the root user login (or account) in Linux. Do you have any comments, suggestions or questions, feel free to reach us via the feedback form below.

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In this article, we will briefly talk about ports in computer networking and move to how you can list all open ports in Linux.

In computer networking, and more definitely in software terms, a port is a logical entity which acts as a endpoint of communication to identify a given application or process on an Linux operating system. It is a 16-bit number (0 to 65535) which differentiates one application from another on end systems.

The two most popular Internet transport protocols, Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) and other less known protocols use port numbers for communication sessions (source and destination port numbers in conjunction with the source and destination IP addresses).

In addition, a combination of an IP address, port and protocol such as TCP/UDP is known as a socket, and every service must have a unique socket.

Below are the different categories of ports:

1. 0-1023 – the Well Known Ports, also referred to as System Ports.
2. 1024-49151 – the Registered Ports, also known as User Ports.
3. 49152-65535 – the Dynamic Ports, also referred to as the Private Ports.

You can view a list of different applications and port/protocol combination in /etc/services file in Linux using cat command:

$ cat /etc/services 
OR
$ cat /etc/services | less

# /etc/services:
# $Id: services,v 1.48 2009/11/11 14:32:31 ovasik Exp $
#
# Network services, Internet style
# IANA services version: last updated 2009-11-10
#
# Note that it is presently the policy of IANA to assign a single well-known
# port number for both TCP and UDP; hence, most entries here have two entries
# even if the protocol doesn't support UDP operations.
# Updated from RFC 1700, ``Assigned Numbers'' (October 1994).  Not all ports
# are included, only the more common ones.
#
# The latest IANA port assignments can be gotten from
#       http://www.iana.org/assignments/port-numbers
# The Well Known Ports are those from 0 through 1023.
# The Registered Ports are those from 1024 through 49151
# The Dynamic and/or Private Ports are those from 49152 through 65535
#
# Each line describes one service, and is of the form:
#
# service-name  port/protocol  [aliases ...]   [# comment]

tcpmux          1/tcp                           # TCP port service multiplexer
tcpmux          1/udp                           # TCP port service multiplexer
rje             5/tcp                           # Remote Job Entry
rje             5/udp                           # Remote Job Entry
echo            7/tcp
echo            7/udp
discard         9/tcp           sink null
discard         9/udp           sink null
systat          11/tcp          users
systat          11/udp          users
daytime         13/tcp
daytime         13/udp
qotd            17/tcp          quote
qotd            17/udp          quote
msp             18/tcp                          # message send protocol
msp             18/udp                          # message send protocol
chargen         19/tcp          ttytst source
chargen         19/udp          ttytst source
ftp-data        20/tcp
ftp-data        20/udp
# 21 is registered to ftp, but also used by fsp
ftp             21/tcp
ftp             21/udp          fsp fspd
ssh             22/tcp                          # The Secure Shell (SSH) Protocol
ssh             22/udp                          # The Secure Shell (SSH) Protocol
telnet          23/tcp
telnet          23/udp

To list all open ports or currently running ports including TCP and UDP in Linux, we will use netstat, is a powerful tool for monitoring network connections and statistics.

$ netstat -lntu

Proto Recv-Q Send-Q Local Address               Foreign Address             State      
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      
tcp        0      0 0.0.0.0:3306                0.0.0.0:*                   LISTEN      
tcp        0      0 0.0.0.0:25                  0.0.0.0:*                   LISTEN      
tcp        0      0 :::22                       :::*                        LISTEN      
tcp        0      0 :::80                       :::*                        LISTEN      
tcp        0      0 :::25                       :::*                        LISTEN      
udp        0      0 0.0.0.0:68                  0.0.0.0:*                               

Where,

1. -l – prints only listening sockets
2. -n – shows port number
3. -t – enables listing of tcp ports
4. -u – enables listing of udp ports

You can also use ss command, a well known useful utility for examining sockets in a Linux system. Run the command below to list all your open TCP and UCP ports:

$ ss -lntu

Netid State      Recv-Q Send-Q               Local Address:Port       Peer Address:Port 
udp   UNCONN     0      0                    *:68                     *:*     
tcp   LISTEN     0      128                  :::22                    :::*     
tcp   LISTEN     0      128                  *:22                     *:*     
tcp   LISTEN     0      50                   *:3306                   *:*     
tcp   LISTEN     0      128                  :::80                    ::*     
tcp   LISTEN     0      100                  :::25                    :::*     
tcp   LISTEN     0      100                  *:25  

Make it a point to read through the man pages of the commands above for more usage information.

In summary, understanding the concept of ports in computer networking is very vital for system and network administrators. You can as well go through this netstat guide with simple, precise and well explained examples.

Last but not least, get in touch with us by sharing other methods for listing open ports in Linux or asking a question via the response form below.

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One of the renowned search tool on Unix-like systems which can be used to search for anything whether it be a file, or a line or multiple lines in file is grep utility. It is very vast in functionality which can be attributed to the large number of options it supports like: searching using string pattern, or reg-ex pattern or perl based reg-ex etc.

Due its varying functionalities, it has many variants including grep, egrep (Extended GREP), fgrep (Fixed GREP), pgrep (Process GREP), rgrep (Recursive GREP) etc. But these variants have minor differences to original grepwhich has made them popular and to be used by various Linux programmers for specific tasks.

Main thing that remains to be investigated is what are the differences between the three main variants i.e. ‘grep’, ‘egrep’ and ‘fgrep’ of grep that makes Linux users choose one or the other version as per requirement.

Some Special Meta-Characters of grep

1. + – Equivalent to one or more occurrences of previous character.
2. ? – This denotes almost 1 repetition of previous character. Like: a? Would match ‘a’ or ‘aa’.
3. ( – Start of alternation expression.
4. ) – End of alternation expression.
5. | – Matching either of the expression separated by '|'. Like: “(a|b)cde” would match either ‘abcde’ or ‘bbcde’.
6. { – This meta-character indicates start of range specifier. Like: “a{2}” matches “aa” in file i.e. a 2 times.
7. } – This meta-character indicates end of range specifier.

Differences Between grep, egrep and fgrep

Some main differences between grep, egrep and fgrep can be highlighted as follows. For this set of examples we are assuming the file on which operation is being performed to be:

Grep Command

grep or Global Regular Expression Print is the main search program on Unix-like systems which can search for any type of string on any file or list of files or even output of any command.

Suggested Read: 12 Practical Examples of Linux grep Command

It uses Basic Regular Expressions apart from normal strings as a search pattern. In Basic Regular Expressions (BRE), meta-characters like: '{','}','(',')','|','+','?' loose their meaning and are treated as normal characters of string and need to be escaped if they are to be treated as special characters.

Suggested Read: 11 Advance ‘Grep’ Commands on Character Classes and Bracket Expressions

Also, grep uses Boyer-Moore algorithm for fast searching any string or regular expression.

$ grep -C 0 '(f|g)ile' check_file
$ grep -C 0 '\(f\|g\)ile' check_file

Like here, when the command is run without escaping '(' ')' and '|' then it searched for the complete string i.e. “(f|g)ile” in the file. But when the special characters were escaped, then instead of treating them as part of string, grep treated them as meta-characters and searched for words “file” or “gile” in the file.

Egrep Command

Egrep or grep -E is another version of grep or the Extended grep. This version of grep is efficient and fast when it comes to searching for a regular expression pattern as it treats meta-characters as is and doesn’t substitute them as strings like in grep, and hence you are freed from the burden of escaping them as in grep. It uses ERE or the Extended Regular Expression set.

In case of egrep, even if you do not escape the meta-characters, it would treat them as special characters and substitute them for their special meaning instead of treating them as part of string.

$ egrep -C 0 '(f|g)ile' check_file
$ egrep -C 0 '\(f\|g\)ile' check_file

Like here, egrep searched for “file” string when the meta-characters were not escaped as it would mean by the meaning of these characters. But, when these characters were escaped, then egrep treated them as part of string and searched for complete string “(f|g)ile” in the file.

fgrep Command

Fgrep or the Fixed grep or grep -F is yet another version of grep which is fast in searching when it comes to search for the entire string instead of regular expression as it doesn’t recognize the regular expressions, neither any meta-characters. For searching any direct string, this is the version of grep which should be selected.

Fgrep searches for complete string and doesn’t even recognize special characters as part of regular expression even if escaped or not escaped.

$ fgrep -C 0 '(f|g)ile' check_file
$ fgrep -C 0 '\(f\|g\)ile' check_file

Like, when meta-characters were not escaped, fgrep searched for the complete string “(f|g)ile” in the file, and when the meta-characters were escaped, then the fgrep command searched for “\(f\|g\)ile” all characters as is in the file.

We’ve already covered some practical examples of grep command you can read them here, if you want to get more out of grep command in Linux.

Learn 12 Practical Examples of Linux grep Command

Conclusion

Above highlighted are the differences between ‘grep’, ‘egrep’ and ‘fgrep’. Apart from difference in the set of regular expressions used, and speed of execution, rest command line parameters remain same for all the three versions of grep and even instead of “egrep” or “fgrep”, “grep -E” or “grep -F” are recommended to be used.

If you find any other differences between these three versions of grep, do mention them in your comments.

Source

In our previous article, we have covered some useful command line networking utilities for Sysadmin’s for network management, troubleshooting and debugging on Linux. We mentioned some networking commands that are still included and supported in many Linux distributions, but are now, in reality, deprecated or obsoleted and therefore should be carry out in favor of more present-day replacements.

Although these networking tools/utilities are still available in official repositories of mainstream Linux distributions, but they do not actually come pre-installed by default.

This is evident in Enterprise Linux distributions, a number of popular networking commands no longer work on RHEL/CentOS 7, while they actually work on RHEL/CentOS 6. Latest Debian and Ubuntu releases don’t include them as well.

In this article, we will share deprecated Linux networking commands and their replacements. These commands include ifconfig, netstat, arp, iwconfig, iptunnel, nameif, as well as route.

All the listed programs with exception of iwconfig are found in the net-tools package which has not been under active maintenance for so many years.

Importantly, you should keep in mind that “unmaintained software is dangerous”, it poses a great security risk to your Linux system. The modern replacement for net-tools is iproute2 – an assortment of utilities for controlling TCP/IP networking in Linux.

The following table shows the summary of the exact deprecated commands and their replacements, that you should take note of.

You will find more details about some of the replacements in these following guides.

1. ifconfig vs ip: What’s Difference and Comparing Network Configuration
2. 10 Useful “IP” Commands to Configure Network Interfaces

Reference: Doug Vitale Tech Blog post.
Net-tools Project Home: https://sourceforge.net/projects/net-tools/
iproutre2 Description Page: https://wiki.linuxfoundation.org/networking/iproute2

All in all, it’s good to keep these changes in mind, as most of these obsolete tools will totally be replaced sometime in the future. Old habits die hard but you have to move on. In addition, installing and using unmaintained packages on your Linux system is an insecure and dangerous practice.

Source

Exodus is a simple yet useful program for easily and securely copying Linux ELF binaries from one system to another. For example, if you have htop (Linux Process Monitoring Tool) installed on your desktop machine, but not installed on your remote Linux server, exodus gives a way to copy/install the htop binary from the desktop machine to the remote server.

It bundles all of the binary’s dependencies, compiling a statically linked wrapper for the executable that invokes the relocated linker directly, and installing the bundle in the ~/.exodus/ directory, on the remote system.

You can see it in action here.

Install Exodus in Linux Systems

You can install exodus using Python PIP package manager, as follows. The command below will perform a user specific installation (only for the account you have logged on with).

$ sudo apt install python-pip                [Install PIP On Debian/Ubuntu]
$ sudo yum install epel-release python-pip   [Install PIP On CentOS/RHEL]
$ sudo dnf install python-pip	             [Install PIP On Fedora]
$ pip install --user exodus-bundler          [Install Exodus in Linux] 

Next, add the directory ~/.local/bin/ to your PATH variable in your ~/.bashrc file, in order to run the exodus executable like any other system command.

export PATH="~/.local/bin/:${PATH}"

Save and close the file. Then open another terminal window to start using exodus.

Note: It is also highly recommended that you install gcc and one of either musl libc or diet libc (C libraries used to compile small statically linked launchers for the bundled applications), on the machine where you’ll be packaging binaries.

Use Exodus to Copy Local Binary To a Remote Linux System

Once you have installed exodus, you can copy a local binary (htop tool) to a remote machine by simply running the following command.

$ exodus htop | ssh tecmint@server3

Then login to the remote machine, and add the directory /home/tecmint/.exodus/bin to your PATH in your ~/.bashrc file, in order to run the htop like any other system command.

export PATH="~/.exodus/bin:${PATH}"

Save and close the file, then source it as follows, for the changes to take effect.

$ source ~/.bashrc

Now you should be able to run htop on your remote Linux machine.

$ htop

If you have two or more binaries with the same name (for example, more than one version of htop installed on your system, one /usr/bin/htop and another /usr/local/bin/htop), you can copy and install them in parallel with the -r flag, it enables for assigning of aliases for each binary on the remote machine.

The following command will install the two htop versions in parallel with /usr/bin/grep called htop-1 and /usr/local/bin/htop called htop-2 as shown.

$ exodus -r htop-1 -r htop-2 /usr/bin/htop /usr/local/bin/htop | ssh tecmint@server3

Attention: Exodus has a number of limitations and it may fail to work with non-ELF binaries, incompatible CPU architectures, incompatible Glibc and kernel versions, driver dependent libraries, pro-grammatically loaded libraries and non-library dependencies.

For more information, see the exodus help page.

$ exodus -h           

Exodus Github repository: https://github.com/intoli/exodus

Conclusion

Exodus is simple yet powerful tool for copying binaries from one Linux machine to another remote Linux system. Try it out and give us your feedback via the comment form below.

Source

There are plenty of network monitoring tools you can find in the Linux ecosystem, that can generate for you a summary of the total number of devices on a network including all their IP addresses and more.

However, sometimes what you actually need may be a simple command line tool that can provide you the same information by running a single command.

This tutorial will explain you how to find out all live hosts IP addresses connected to a given network. Here, we will use Nmap tool to find out all IP addresses of devices connected on a same network.

Suggested Read: 29 Examples of ‘Nmap’ Commands for System/Network Administration

The Nmap (short form for Network Mapper) is an open source, powerful and a very versatile command line tool for exploring networks, perform security scans, network audit and finding open ports on remote machine and so much more.

In case you do not have Nmap installed on your system, run the appropriate command below for your distribution to install it:

$ sudo yum install nmap         [On RedHat based systems]
$ sudo dnf install nmap         [On Fedora 22+ versions]
$ sudo apt-get install nmap     [On Debian/Ubuntu based systems]

Once you have Nmap installed, the syntax for using it is:

$ nmap  [scan type...]  options  {target specification}

Where the argument {target specification}, can be replaced by hostnames, IP addresses, networks and so on.

Therefore to list the IP addresses of all hosts connected to a given network, first of all identify the network and its subnet mask using the ifconfig command or ip command like so:

$ ifconfig
OR
$ ip addr show

Next, run the Nmap command below:

$ nmap  -sn  10.42.0.0/24

In the command above:

1. -sn – is the type of scan, which means a ping scan. By default, Nmap performs port scanning, but this scan will disable port scanning.
2. 10.42.0.0/24 – is the target network, replace it with your actual network.

For a comprehensive usage information, make an effort to look into Nmap man page:

$ man nmap

Else, run Nmap without any options and arguments to view a summarized usage information:

$ nmap

In addition, for those interested in learning security scanning techniques in Linux, you can read through this practical guide to Nmap in Kali Linux.

Well, that’s it for now, remember to send us your questions or comments through the response form below. You can as well share with us other methods for listing the IP addresses of all devices connected to a given network.

Source

We keep on accomplishing a task conventionally until we come to know that it can be done in a much better way the other way. In continuation of our Linux Tips and Trick Series, I am here with the below four tips that will going to help you in lots of ways. Here we go!

1. You are supposed to create a long/complex directory tree similar to given below. What is the most effective way to achieve this?

Directory tree structure to achieve as suggested below.

$ cd /home/$USER/Desktop
$ mkdir tecmint
$ mkdir tecmint/etc
$ mkdir tecmint/lib
$ mkdir tecmint/usr
$ mkdir tecmint/bin
$ mkdir tecmint/tmp
$ mkdir tecmint/opt
$ mkdir tecmint/var
$ mkdir tecmint/etc/x1
$ mkdir tecmint/usr/x2
$ mkdir tecmint/usr/x3
$ mkdir tecmint/tmp/Y1
$ mkdir tecmint/tmp/Y2
$ mkdir tecmint/tmp/Y3
$ mkdir tecmint/tmp/Y3/z

The above scenario can simply be achieved by running the below 1-liner command.

$ mkdir -p /home/$USER/Desktop/tecmint/{etc/x1,lib,usr/{x2,x3},bin,tmp/{Y1,Y2,Y3/z},opt,var}

To verify you may use tree command. If not installed you may apt or yum the package ‘tree‘.

$ tree tecmint

We can create directory tree structure of any complexity using the above way. Notice it is nothing other than a normal command but its using {} to create hierarchy of directories. This may prove very helpful if used from inside of a shell script when required and in general.

2. Create a file (say test) on your Desktop (/home/$USER/Desktop) and populate it with the below contents.

ABC
DEF
GHI
JKL
MNO
PQR
STU
VWX
Y
Z

What a normal user would do in this scenario?

a. He will create the file first, preferably using touch command, as:

$ touch /home/$USER/Desktop/test

b. He will use a text editor to open the file, which may be nano, vim, or any other editor.

$ nano /home/$USER/Desktop/test

c. He will then place the above text into this file, save and exit.

So regardless of time taken by him/her, he need at-least 3 steps to execute the above scenario.

What a smart experienced Linux-er will do? He will just type the below text in one-go on terminal and all done. He need not do each action separately.

cat << EOF > /home/$USER/Desktop/test
ABC
DEF
GHI
JKL
MNO
PQR
STU
VWX
Y
Z
EOF

You may use ‘cat‘ command to check if the file and its content were created successfully or not.

$ cat /home/avi/Desktop/test

3. We deal with archives (specially TAR balls) very often on Linux. In many cases we have to use that TAR ball on some location other than Downloads folder. What we do in this scenario?

We normally do two things in this scenario.

a. Copy/Move the tar ball and extract it at destination, as:

$ cp firefox-37.0.2.tar.bz2 /opt/
or
$ mv firefox-37.0.2.tar.bz2 /opt/

b. cd to /opt/ directory.

$ cd /opt/

c. Extract the Tarball.

# tar -jxvf firefox-37.0.2.tar.bz2 

We can do this the other way around.

We will extract the Tarball where it is and Copy/Move the extracted archive to the required destination as:

$ tar -jxvf firefox-37.0.2.tar.bz2 
$ cp -R firefox/  /opt/
or
$ mv firefox/ /opt/

In either case the work is taking two or steps to complete. The professional can complete this task in one step as:

$ tar -jxvf firefox-37.0.2.tar.bz2 -C /opt/

The option -C makes tar extract the archive in the specified folder (here /opt/).

No it is not about an option (-C) but it is about habits. Make a habit of using option -C with tar. It will ease your life. From now don’t move the archive or copy/move the extracted file, just leave the TAR-ball in the Downloadsfolder and extract it anywhere you want.

4. How we kill a process in a traditional way?

In most general way, we first list all the process using command ps -A and pipeline it with grep to find a process/service (say apache2), simply as:

$ ps -A | grep -i apache2

Sample Output

1006 ?        00:00:00 apache2
 2702 ?        00:00:00 apache2
 2703 ?        00:00:00 apache2
 2704 ?        00:00:00 apache2
 2705 ?        00:00:00 apache2
 2706 ?        00:00:00 apache2
 2707 ?        00:00:00 apache2

The above output shows all currently running apache2 processes with their PID’s, you can then use these PID’s to kill apache2 with the help of following command.

# kill 1006 2702 2703 2704 2705 2706 2707

and then cross check if any process/service with the name ‘apache2‘ is running or not, as:

$ ps -A | grep -i apache2

However we can do it in a more understandable format using utilities like pgrep and pkill. You may find relevant information about a process just by using pgrep. Say you have to find the process information for apache2, you may simply do:

$ pgrep apache2

Sample Output

15396
15400
15401
15402
15403
15404
15405

You may also list process name against pid by running.

$ pgrep -l apache2

Sample Output

15396 apache2
15400 apache2
15401 apache2
15402 apache2
15403 apache2
15404 apache2
15405 apache2

To kill a process using pkill is very simple. You just type the name of resource to kill and you are done. I have written a post on pkill which you may like to refer here : https://www.tecmint.com/how-to-kill-a-process-in-linux/.

To kill a process (say apache2) using pkill, all you need to do is:

# pkill apache2

You may verify if apache2 has been killed or not by running the below command.

$ pgrep -l apache2

It returns the prompt and prints nothing means there is no process running by the name of apache2.

That’s all for now.

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To compress a file(s), is to significantly decrease the size of the file(s) by encoding data in the file(s) using less bits, and it is normally a useful practice during backup and transfer of a file(s) over a network. On the other hand, decompressing a file(s) means restoring data in the file(s) to its original state.

Suggested Read: Learn Linux ‘tar’ Command with This 18 Examples

There are several file compression and decompression tools available in Linux such as gzip, 7-zip, Lrzip, PeaZipand many more.

In this tutorial, we will look at how to compress and decompress .bz2 files using the bzip2 tool in Linux.

Bzip2 is a well known compression tool and it’s available on most if not all the major Linux distributions, you can use the appropriate command for your distribution to install it.

$ sudo apt install bzip2     [On Debian/Ubuntu] 
$ sudo yum install  bzip2    [On CentOS/RHEL]
$ sudo dnf install bzip2     [On Fedora 22+]

The conventional syntax of using bzip2 is:

$ bzip2 option(s) filenames 

How to Use “bzip2” to Compress Files in Linux

You can compress a file as below, where the flag -z enables file compression:

$ bzip2 filename
OR
$ bzip2 -z filename

To compress a .tar file, use the command format:

$ bzip2 -z backup.tar

Important: By default, bzip2 deletes the input files during compression or decompression, to keep the input files, use the -k or --keep option.

In addition, the -f or --force flag will force bzip2 to overwrite an existing output file.

------ To keep input file  ------
$ bzip2 -zk filename
$ bzip2 -zk backup.tar

You can as well set the block size to 100k upto 900k, using -1 or --fast to -9 or –best as shown in the below examples:

$ bzip2 -k1  Etcher-linux-x64.AppImage
$ ls -lh  Etcher-linux-x64.AppImage.bz2 
$ bzip2 -k9  Etcher-linux-x64.AppImage 
$ bzip2 -kf9  Etcher-linux-x64.AppImage 
$ ls -lh Etcher-linux-x64.AppImage.bz2

The screenshot below shows how to use options to keep the input file, force bzip2 to overwrite an output file and set the block size during compression.

How to Use “bzip2” to Decompress Files in Linux

To decompress a .bz2 file, make use of the -d or --decompress option like so:

$ bzip2 -d filename.bz2

Note: The file must end with a .bz2 extension for the command above to work.

$ bzip2 -vd Etcher-linux-x64.AppImage.bz2 
$ bzip2 -vfd Etcher-linux-x64.AppImage.bz2 
$ ls -l Etcher-linux-x64.AppImage 

To view the bzip2 help page and man page, type the command below:

$ bzip2  -h
$ man bzip2

Lastly, with the simple elaborations above, I believe you are now capable of compressing and decompressing .bz2 files using the bzip2 tool in Linux. However, for any questions or feedback, reach us using the comment section below.

Importantly, you may want to go over a few important Tar command examples in Linux so as to learn using the tar utility to create compressed archive files.

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