Linux Blimp

Process management is one of the important aspects of System Administration in Linux, and it includes killing of processes using the kill command.

In this how-to, we shall look at killing of less productive or unwanted processes on your Linux system.

What is a Process in Linux?

A process on a Linux system can be a running occurrence of an application or program. You can also refer to processes as tasks executing in the operating system.

When a process is running, it keeps on shifting from one state to another and a process can in one of the following states:

1. Running: meaning the process is either executing or it is just set to be executed.
2. Waiting: meaning that the process is waiting for an event or for a system resource to carry out a task.

There are two types of waiting process under Linux namely interruptible and uninterruptible.

A waiting process that can be interrupted by signals is called Interruptible, while a waiting process that is directly waiting on hardware conditions and cannot be interrupted under any conditions is called uninterruptible.

1. Stopped: meaning that the process has been stopped, using a signal.
2. Zombie: meaning the process has been stopped abruptly and is dead.

With this brief overview let us now look at ways of killing processes in a Linux system. We’ve already covered a few articles on ways to kill Linux running processes us using kill, pkill, killall and xkill, you can read them below.

1. A Guide to Manage Linux Processes Using Kill, Pkill and Killall Commands
2. How to Kill Unresponsive Linux Processes Using Xkill Command

When killing processes, the kill command is used to send a named signal to a named process or groups of processes. The default signal is the TERM signal.

Remember that the kill command can be a built-in function in many modern shells or external located at /bin/kill.

How to Find Process PID in Linux

In Linux every process on a system has a PID (Process Identification Number) which can be used to kill the process.

You can identify the PID of any process by using the pidof command as follows:

$ pidof firefox
$ pidof chrome
$ pidof gimp-2.8

How to Kill Processes in Linux

Once you find the process PID, let us now look at how to kill processes. In this first example, I am going to first get the PID of the process and then send a signal to it.

I want to kill gimp process, so I will do it as follows:

$ pidof gimp-2.8
$ kill 9378

To verify that the process has been killed, run the pidof command and you will not be able to view the PID.

$ pidof gimp-2.8

You can also send a named signal to the process by using the signal name or numbers as follows:

$ pidof vlc
$ kill -SIGTERM 9541
$ pidof vlc

Using the signal number to kill a process:

$ pidof banshee
$ kill -9 9647
$ pidof banshee

In the above example, the number 9 is the signal number for the SIGKILL signal.

How to Kill Multiple Process PID’s in Linux

To kill more than one process, pass the PID(s) to the kill command as follows:

$ pidof gimp-2.8
$ pidof vlc
$ pidof banshee
$ kill -9 9734 9747 9762

Summary

There are many other ways of killing processes in Linux, these few examples just help to give you an overview of killing processes. Do let us know how you kill processes in Linux? and also tell other ways if any via comments.

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ncdu (NCurses Disk Usage) is a command line version of the most popular “du command“. It is based on ncurses and provides a fastest way to analyse and track what files and directories are using your disk space in Linux. It provides an excellent ncurses based interface to display the information in more intuitive way like columns for how much disk space used in megabytes, gigabytes and graphical bar usage, file/directory names, file deletion, refresh, etc. ncdu aims to be simple, fast and easy to use program and runs on any minimal Linux/Unix based system with ncurses installed.

This article explains you through the process of installing and using NCDU program on a Linux system.

Installing ncdu (NCurses Disk Usage)

The “ncdu” package is not available under RHEL, CentOS, Fedora, Scientific Linux distributions, you must have epel repository enabled on your system to install it using yum command.

# yum install ncdu

The “ncdu” utility is available on Ubuntu, Linux Mint and Debian from the package manager system, use the following apt-get command to install it.

$ sudo apt-get install ncdu

How Do I Use ncdu

# ncdu

 ┌───ncdu help─────────────────1:Keys───2:Format───3:About─────┐
 │         						       │
 │   up, 	k  Move cursor up                              │
 │   down, 	j  Move cursor down                            │
 │   right/enter   Open selected directory                     │
 │   left, <, 	h  Open parent directory                       │
 │   	      	n  Sort by name (ascending/descending)         │
 │   		s  Sort by size (ascending/descending)         │
 │ 		d  Delete selected file or directory           │
 │  		t  Toggle dirs before files when sorting       │
 │  		g  Show percentage and/or graph                │
 │ 		a  Toggle between apparent size and disk usage │
 │		e  Show/hide hidden or excluded files          │
 │           	i  Show information about selected item        │
 │           	r  Recalculate the current directory           │
 │           	q  Quit ncdu                                   │
 │          	                                               │
 │                                     Press q to continue     │
 └─────────────────────────────────────────────────────────────┘

Source

Linux administrator should be familiar with CLI environment. Since GUI mode in Linux servers is not a common to be installed. SSH may the most popular protocol to enable Linux administrator to manage the servers via remote in secure way. Built-in with SSH command there is SCP command. SCP is used to copy file(s) between servers in secure way.

The below command will read as “copy source_file_name” into “destination_folder” at “destination_host” using “username account”.

Basic syntax of SCP

scp source_file_name username@destination_host:destination_folder

There are much parameters in SCP command that you can use. Here are the parameters that may useful on daily basis usage.

Provide the detail information of SCP process using -v parameter

Basic SCP command without parameter will copy the files in background. User will see nothing unless the process is done or some error appears. You can use “-v” parameter to print debug information into the screen. It can help you debugging connection, authentication and configuration problems.

pungki@mint ~/Documents $ scp -v Label.pdf mrarianto@202.x.x.x:.

Sample Output

Executing: program /usr/bin/ssh host 202.x.x.x, user mrarianto, command scp -v -t .
OpenSSH_6.0p1 Debian-3, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 202.x.x.x [202.x.x.x] port 22.
debug1: Connection established.
debug1: Host '202.x.x.x' is known and matches the RSA host key.
debug1: Found key in /home/pungki/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: Next authentication method: password
mrarianto@202.x.x.x's password:
debug1: Authentication succeeded (password).
Authenticated to 202.x.x.x ([202.x.x.x]:22).
Sending file modes: C0770 3760348 Label.pdf
Sink: C0770 3760348 Label.pdf
Label.pdf 100% 3672KB 136.0KB/s 00:27
Transferred: sent 3766304, received 3000 bytes, in 65.2 seconds
Bytes per second: sent 57766.4, received 46.0
debug1: Exit status 0

Provide modification times, access times, and modes from original files

The “-p” parameter will help you on this. An estimated time and the connection speed will appear on the screen.

pungki@mint ~/Documents $ scp -p Label.pdf mrarianto@202.x.x.x:.

Sample Output

mrarianto@202.x.x.x's password:
Label.pdf 100% 3672KB 126.6KB/s 00:29

Make file transfer faster using -C parameter

One of parameter that can faster your file transfer is “-C” parameter. The “-C” parameter will compress your files on the go. The unique thing is the compression is only happen in the network. When the file is arrived to the destination server, it will returning into the original size as before the compression happen.

Take a look of these commands. It is using a single file of 93 Mb.

pungki@mint ~/Documents $ scp -pv messages.log mrarianto@202.x.x.x:.

Sample Output

Executing: program /usr/bin/ssh host 202.x.x.x, user mrarianto, command scp -v -p -t .
OpenSSH_6.0p1 Debian-3, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 202.x.x.x [202.x.x.x] port 22.
debug1: Connection established.
debug1: identity file /home/pungki/.ssh/id_rsa type -1
debug1: Found key in /home/pungki/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: Trying private key: /home/pungki/.ssh/id_rsa
debug1: Next authentication method: password
mrarianto@202.x.x.x's password:
debug1: Authentication succeeded (password).
Authenticated to 202.x.x.x ([202.x.x.x]:22).
debug1: Sending command: scp -v -p -t .
File mtime 1323853868 atime 1380425711
Sending file timestamps: T1323853868 0 1380425711 0
messages.log 100% 93MB 58.6KB/s 27:05
Transferred: sent 97614832, received 25976 bytes, in 1661.3 seconds
Bytes per second: sent 58758.4, received 15.6
debug1: Exit status 0

Copying file without “-C” parameter will result 1661.3 second. Yo may compare the result to the command below which using “-C” parameter.

pungki@mint ~/Documents $ scp -Cpv messages.log mrarianto@202.x.x.x:.

Sample Output

Executing: program /usr/bin/ssh host 202.x.x.x, user mrarianto, command scp -v -p -t .
OpenSSH_6.0p1 Debian-3, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 202.x.x.x [202.x.x.x] port 22.
debug1: Connection established.
debug1: identity file /home/pungki/.ssh/id_rsa type -1
debug1: Host '202.x.x.x' is known and matches the RSA host key.
debug1: Found key in /home/pungki/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: Next authentication method: publickey
debug1: Trying private key: /home/pungki/.ssh/id_rsa
debug1: Next authentication method: password
mrarianto@202.x.x.x's password:
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (password).
Authenticated to 202.x.x.x ([202.x.x.x]:22).
debug1: channel 0: new [client-session]
debug1: Sending command: scp -v -p -t .
File mtime 1323853868 atime 1380428748
Sending file timestamps: T1323853868 0 1380428748 0
Sink: T1323853868 0 1380428748 0
Sending file modes: C0600 97517300 messages.log
messages.log 100% 93MB 602.7KB/s 02:38
Transferred: sent 8905840, received 15768 bytes, in 162.5 seconds
Bytes per second: sent 54813.9, received 97.0
debug1: Exit status 0
debug1: compress outgoing: raw data 97571111, compressed 8806191, factor 0.09
debug1: compress incoming: raw data 7885, compressed 3821, factor 0.48

As you can see, when you are using compression, transfer process is done in 162.5 second. It is 10 times faster than not using “-C” parameter. If you are copying a lot files across the network, “-C” parameter would help you to decrease the total time you need.

The thing that we should notice that compression method will not work on any files. When the source file is already compressed, you will not find any improvement there. Files such as .zip, .rar, pictures, and .iso files will not affected by “-C” parameter.

Select another cipher to encrypt files

By default SCP using “AES-128” to encrypt files. If you want to change to another cipher to encrypt it, you can use “-c” parameter. Take a look of this command.

pungki@mint ~/Documents $ scp -c 3des Label.pdf mrarianto@202.x.x.x:.

mrarianto@202.x.x.x's password:
Label.pdf 100% 3672KB 282.5KB/s 00:13

Above command tell SCP to use 3des algorithm to encrypt file. Please be careful that this parameter using “-c” not “-C“.

Limiting bandwidth usage

Another parameter that may useful is “-l” parameter. The “-l” parameter will limit the bandwidth to use. It will be useful if you do an automation script to copy a lot of file, but you don’t want the bandwidth is drained by the SCPprocess.

pungki@mint ~/Documents $ scp -l 400 Label.pdf mrarianto@202.x.x.x:.

mrarianto@202.x.x.x's password:
Label.pdf 100% 3672KB 50.3KB/s 01:13

The 400 value behind “-l” parameter is mean that we limit the bandwidth for SCP process only 50 KB/sec. One thing to remember that bandwidth is specified in Kilobits/sec (kbps). It is mean that 8 bits equal with 1 byte.

While SCP counts in Kilobyte/sec (KB/s). So if you want to limit your bandwidth for SCP maximum only 50 KB/s, you need to set it into 50 x 8 = 400.

Specify specific port to use with SCP

Usually SCP is using port 22 as a default port. But for security reason, you may change the port into another port. For example, we are using port 2249. Then the command should be like this.

pungki@mint ~/Documents $ scp -P 2249 Label.pdf mrarianto@202.x.x.x:.

mrarianto@202.x.x.x's password:
Label.pdf 100% 3672KB 262.3KB/s 00:14

Make sure that it use capital “P” not “p“, since “p” is already used for preserved times and modes.

Copy files inside directory recursively

Sometimes we need to copy directory and all files / directories inside it. It will be better if we can do it in 1command. SCP support that scenario using “-r” parameter.

pungki@mint ~/Documents $ scp -r documents mrarianto@202.x.x.x:.

mrarianto@202.x.x.x's password:
Label.pdf 100% 3672KB 282.5KB/s 00:13
scp.txt 100% 10KB 9.8KB/s 00:00

When the copy process is done, at the destination server you will found a directory named “documents” with all it’s files. The folder “documents” is automatically created.

Disable progress meter and warning / diagnostic message

If you choose not to see progress meter and warning / diagnostic messages from SCP, you may disable it using “-q” parameter. Here’s the example.

pungki@mint ~/Documents $ scp -q Label.pdf mrarianto@202.x.x.x:.

mrarianto@202.x.x.x's password:
pungki@mint ~/Documents $

As you can see, after the you enter the password, there is no any information about SCP process. After the process is complete, you will be see a prompt again.

Copy files using SCP through Proxy

Proxy server is usually used in office environment. Natively, SCP is not proxy configured. When your environment using proxy, you have to “tell” SCP to communicate with the proxy.

Here’s the scenario. The proxy address is 10.0.96.6 and the proxy port is 8080. The proxy also implemented user authentication. First, you need to create “~/.ssh/config” file. Second you put this command inside it.

ProxyCommand /usr/bin/corkscrew 10.0.96.6 8080 %h %p ~/.ssh/proxyauth

Then you need to create file “~/.ssh/proxyauth” which contain.

myusername:mypassword

After that you can do SCP transparently as usual.

Please notice that corkscrew is might not installed yet on your system. On my Linux Mint, I need to install it first, using standard Linux Mint installation procedure.

$ apt-get install corkscrew

For other yum based systems, users can install corkscrew using the following yum command.

# yum install corkscrew

Another thing that since “~/.ssh/proxyauth” file contain your “username” and “password” in clear-text format, please make sure that the file can be accessed by you only.

Select different ssh_config file

For mobile user who often switch between company network and public network, it will be suffer to always change settings in SCP. It is better if we can put a different ssh_config file to match our needs.

Here’s a sample scenario

Proxy is used in company network but not in public network and you are regularly switch network.

pungki@mint ~/Documents $ scp -F /home/pungki/proxy_ssh_config Label.pdf

mrarianto@202.x.x.x:.
mrarianto@202.x.x.x's password:
Label.pdf 100% 3672KB 282.5KB/s 00:13

By default “ssh_config” file per user will be placed in “~/.ssh/config“. Creating a specific “ssh_config” file with proxy compatible, will make you easier to switch between networks.

When you are on company network, you can use “-F” parameter. When you are on public network, you can skip “-F” parameter.

That’s all about SCP. You can see man pages of SCP for more detail. Please feel free to leave comments and suggestions.

Source

File Transfer Protocol (FTP) was widely used protocol to transfer files or data remotely in unencrypted format which is not secure way to communicate. As we all know that File Transfer Protocol is not at all secure because all transmissions happens in clear text and the data can be readable by anyone during sniffing the packets on the network.

So, basically FTP can be used in limited cases or on the networks that you trust. Over the period of time SCPand SSH addresses this security ambiguity and added an encrypted secure layer while transferring data between remote computers.

SFTP (Secure File Transfer Protocol) runs over SSH protocol on standard port 22 by default to establish a secure connection. SFTP has been integrated into many GUI tools (FileZilla, WinSCP, FireFTP etc.).

Security Warnings: Please don’t open SSH port (Secure SHell) globally as this would be a security breaches. You can only open for specific IP from where you are going to transfer or manage files on remote system or vice versa.

1. 5 Best Practices to Secure and Protect SSH Server
2. 10 Wget Command Examples in Linux

This article will guide you 10 sftp command examples to use it through interactive command-line interface.

1. How to Connect to SFTP

By default, same SSH protocol is used to authenticate and establish a SFTP connection. To start an SFTP session, enter the username and remote hostname or IP address at the command prompt. Once authentication successful, you will see a shell with an sftp> prompt.

[root@tecmint ~]# sftp tecmint@27.48.137.6

Connecting to 27.48.137.6...
tecmint@27.48.137.6's password:
sftp>

2. Getting Help

Once, you in the sftp prompt, check the available commands by typing ‘?‘ or ‘help‘ at command prompt.

sftp> ?
Available commands:
cd path                       Change remote directory to 'path'
lcd path                      Change local directory to 'path'
chgrp grp path                Change group of file 'path' to 'grp'
chmod mode path               Change permissions of file 'path' to 'mode'
chown own path                Change owner of file 'path' to 'own'
help                          Display this help text
get remote-path [local-path]  Download file
lls [ls-options [path]]       Display local directory listing
ln oldpath newpath            Symlink remote file
lmkdir path                   Create local directory
lpwd                          Print local working directory
ls [path]                     Display remote directory listing
lumask umask                  Set local umask to 'umask'
mkdir path                    Create remote directory
put local-path [remote-path]  Upload file
pwd                           Display remote working directory
exit                          Quit sftp
quit                          Quit sftp
rename oldpath newpath        Rename remote file
rmdir path                    Remove remote directory
rm path                       Delete remote file
symlink oldpath newpath       Symlink remote file
version                       Show SFTP version
!command                      Execute 'command' in local shell
!                             Escape to local shell
?                             Synonym for help

3. Check Present Working Directory

The command ‘lpwd‘ is used to check the Local present working directory, whereas ‘pwd‘ command is used to check Remote working directory.

sftp> lpwd
Local working directory: /
sftp> pwd
Remote working directory: /tecmint/

1. lpwd – print the current directory on your system
2. pwd – print the current directory on the ftp server

4. Listing Files

Listing files and directories in local as well as remote system.

On Remote

sftp> ls

On Local

sftp> lls

5. Upload File

Put single or multiple files in remote system.

sftp> put local.profile
Uploading local.profile to /tecmint/local.profile

6. Upload Mutiple Files

Putting multiple files on in remote system.

sftp> mput *.xls

6. Download Files

Getting single or multiple files in local system.

sftp> get SettlementReport_1-10th.xls
Fetching /tecmint/SettlementReport_1-10th.xls to SettlementReport_1-10th.xls

Get multiple files on a local system.

sftp> mget *.xls

Note: As we can see by default with get command download file in local system with same name. We can download remote file with different name specifying the name at the end. (This applies only while downloading single file).

7. Switching Directories

Switching from one directory to another directory in local and remote locations.

On Remote

sftp> cd test
sftp>

On Local

sftp> lcd Documents

8. Create Directories

Creating new directories on local and remote locations.

sftp> mkdir test

sftp> lmkdir Documents

9. Remove Directories

Remove directory or file in remote system.

sftp> rm Report.xls

sftp> rmdir sub1

Note: To remove/delete any directory from remote location, the directory must be empty.

10. Exit sFTP Shell

The ‘!‘ command drop us in local shell from where we can execute Linux commands. Type ‘exit‘ command where we can see sftp> prompt return.

sftp> !

[root@sftp ~]# exit
Shell exited with status 1
sftp>

Conclusion

The SFTP is a very useful tool for administrating servers and transferring files to and from (Local and Remote). We hope this tuts will help you to understand the usage of SFTP in some extent.

Source

Have you ever tried to do the partitioning of hard disk larger than 2TB using fdisk utility and wondered why you end up getting a warning to use GPT? Yes, you got that right. We cannot partition a hard disk larger than 2TB using fdisk tool.

In such cases, we can use parted command. The major difference lies in the partitioning formats that fdiskuses DOS partitioning table format and parted uses GPT format.

TIP: You can use gdisk as well instead of parted tool.

In this article, we will show you to add a new disk larger than 2TB to an existing Linux server such as RHEL/CentOS or Debian/Ubuntu.

I am using fdisk and parted utilities to do this configuration.

First list the current partition details using fdisk command as shown.

# fdisk -l

For the purpose of this article, I am attaching a hard disk of 20GB capacity, which can be followed for disk larger than 2TB as well. Once you added a disk, verify the partition table using same fdisk command as shown.

# fdisk -l

Tip: If you are adding a physical hard disk, you may find that partitions already created. In such cases, you can use fdsik to delete the same before using parted.

# fdisk /dev/xvdd

Use d switch for the command to delete the partition and w to write the changes and quit.

Important: You need to be careful while deleting the partition. This will erase the data on the disk.

Now its time to partition a new hard disk using parted command.

# parted /dev/xvdd

Set the partition table format to GPT

(parted) mklabel gpt

Create the Primary partition and assign the disk capacity, here I am using 20GB (in your case it would be 2TB).

(parted) mkpart primary 0GB 20GB

Just for curiosity, let’s see how this new partition is listed in fdisk.

# fdisk /dev/xvdd

Now format and then mount the partition and add the same in /etc/fstab which controls the file systems to be mounted when the system boots.

# mkfs.ext4 /dev/xvdd1

Once partition has been formatted, now it’s time mount the partition under /data1.

# mount /dev/xvdd1 /data1

For permanent mounting add the entry in /etc/fstab file.

/dev/xvdd1     /data1      ext4      defaults  0   0

Important: Kernel should support GPT in order to partition using GPT format. By default RHEL/CentOS have Kernel with GPT support, but for Debian/Ubuntu you need to recompile the kernel after changing the config.

That’s it! In this article, we have shown you how to use the parted command. Share your comments and feedback with us.

Source

All of us might have faced a situation at some point of time or the other while using Linux tar.gz, tar.bz2, tbzcommands. So many archive types, so many commands to remember… Well, not any-more, thanks to dtrx tool.

1. 18 Tar Commands to Create and Extract Archives in Linux
2. How to Open, Extract and Create RAR Files in Linux

What is Dtrx?

Dtrx stands for “Do The Right Extraction“, it’s an open source and very effective command-line application for *nix systems that simplify your job of archive extraction easier.

The dtrx command is an replacement of “tar -zxvf” or “tar -xjf” commands and it provides a one single command to extract archives in a number of different formats including tar, zip, rpm, deb, gem, 7z, cpio, rar and many more. It can also used to decompress files compressed with bzip2, gzip etc.

By default, dtrx extract contents to a dedicated directory and also fixes permission issues (like permission denied) faced by user while extracting content to ensure that the owner can read and write all those files.

Dtrx Features

1. Handles many archive types: It provides only one simple command to extract tar, zip, rar, gz, bz2, xz, rpm, deb, gem, self-extracting zip files and many other formats of exe files.
2. Keeps everything organized: It will extract archives into their own dedicated directories.
3. Sane permissions: It also make sure, user can read and write all those files after extraction, keeping permission intact.
4. Recursive extraction: It can find archives inside the archive and extract those too.

How to Install Dtrx in Linux

The dtrx tool is by default included in Ubuntu repositories, all you’ve to do is simple do a apt-get to install in on your system.

On Debian/Ubuntu/Linux Mint

$ sudo apt-get install dtrx

On RHEL/CentOS/Fedora

On Red Hat based systems, dtrx is not available via default repositories, you need to download a dtrx script and install the program system-wide using below commands as root user.

# wget http://brettcsmith.org/2007/dtrx/dtrx-7.1.tar.gz
# tar -xvf dtrx-7.1.tar.gz 
# cd dtrx-7.1
# python setup.py install --prefix=/usr/local

Sample Output

running install
running build
running build_scripts
creating build
creating build/scripts-2.6
copying and adjusting scripts/dtrx -> build/scripts-2.6
changing mode of build/scripts-2.6/dtrx from 644 to 755
running install_scripts
copying build/scripts-2.6/dtrx -> /usr/local/bin
changing mode of /usr/local/bin/dtrx to 755
running install_egg_info
Creating /usr/local/lib/python2.6/site-packages/
Writing /usr/local/lib/python2.6/site-packages/dtrx-7.1-py2.6.egg-info

How to Use dtrx Command

The dtrx command is sort of like the one ring to rule them all in the Lord of The Rings. Instead of having to remember syntax for each archive, all you have to remember is dtrx command.

1. Extracting Single Archive

For example, I want to extract a archive file called “tecmint27-12-2013.gz“, I only execute dtrx command without using any flags.

[root@tecmint]# dtrx tecmint27-12-2013.gz

Other than simplifying the extraction, it has a bunch of other options like extracting the file to a folder and recursively extracting all other archives inside a given archive.

2. Extracting Multiple Archives

Consider you’ve a file “dtrAll.zip“, consisting of dtr1.zip, dtr2.zip and dtr3.zip each consisting of dtr1,dtr2 and dtr3 respectively. Instead of having to manually first extract the dtrAll zip and then extracting each one of thedtr1, dtr2 and dtr3 you can directly extract it in respective folders by using dtrx and by selecting option “a“, it extracts all the zip files recursively.

[root@tecmint]# dtrx dtrAll.zip

Sample Output

dtrx: WARNING: extracting /root/dtrAll.zip to dtrAll.1
dtrAll.zip contains 3 other archive file(s), out of 3 file(s) total.
You can:
 * _A_lways extract included archives during this session
 * extract included archives this _O_nce
 * choose _N_ot to extract included archives this once
 * ne_V_er extract included archives during this session
 * _L_ist included archives
What do you want to do?  (a/o/N/v/l) a

After, extraction, the contents of the extracted directory can be verified using ls command.

[root@tecmint]# cd dtrAll
[root@tecmint]# ls 

dtr1  dtr1.zip  dtr2  dtr2.zip  dtr3  dtr3.zip

3. Extracting Specific Archive

Let’s say you want to extract the first archive and not archives inside it. By selecting N, it only extracts the given archive and not other archives inside it.

[root@tecmint]# dtrx dtrAll.zip

Sample Output

dtrx: WARNING: extracting /root/dtrAll.zip to dtrAll.1
dtrAll.zip contains 3 other archive file(s), out of 3 file(s) total.
You can:
 * _A_lways extract included archives during this session
 * extract included archives this _O_nce
 * choose _N_ot to extract included archives this once
 * ne_V_er extract included archives during this session
 * _L_ist included archives
What do you want to do?  (a/o/N/v/l) N

The contents of extracted directory can be verified using ls command as shown.

[root@tecmint]# cd dtrAll
[root@tecmint]# ls

dtr1.zip dtr2.zip dtr3.zip

4. Extract Each Layer of Archive

To extract each layer of archive inside archive on a case by case basis i.e., if you want to extract 2nd layer of archives but not the 3rd layer, you can use the “o” option.

Consider you’ve a zip file “dtrNewAll.zip“, which has “dtrAll.zip” and “dtrNew” as it’s contents. Now if you want to extract the contents of “dtrNewAll” and “dtrAll” as well but not of dtr1.zip, dtr2.zip and dtr3.zip, you can use “o” and “n” options as shown below.

# dtrx dtrNewAll.zip

Sample Output

dtrNewAll.zip contains 1 other archive file(s), out of 2 file(s) total.
You can:
 * _A_lways extract included archives during this session
 * extract included archives this _O_nce
 * choose _N_ot to extract included archives this once
 * ne_V_er extract included archives during this session
 * _L_ist included archives
What do you want to do?  (a/o/N/v/l) o

dtrAll.zip contains 3 other archive file(s), out of 3 file(s) total.
You can:
 * _A_lways extract included archives during this session
 * extract included archives this _O_nce
 * choose _N_ot to extract included archives this once
 * ne_V_er extract included archives during this session
 * _L_ist included archives
What do you want to do?  (a/o/N/v/l) n

The contents of extracted directory can be verified using ls command as shown.

[root@tecmint]# cd dtrNewAll
[root@tecmint]# ls

dtrAll  dtrAll.zip  dtrNew

[root@tecmint]# cd dtrAll
[root@tecmint]# ls

dtr1.zip dtr2.zip dtr3.zip

We first select the “o” option which means that all archives inside dtrNewAll will be extracted. Later we select the “n” option for dtrAll.zip which means that the archives inside it dtr1.zip , dtr2.zip and dtr3.zip will not be extracted.

5. Extract meta-data from .deb, .rpm and .gem files

The “-m” option extract the meta-data from .deb, .rpm and .gem archives, instead of their normal contents. Here is an example of the command.

[root@tecmint]# dtrx -m openfire_3.8.2_all.deb 
[root@tecmint]# dtrx -m openfire-3.8.2-1.i386.rpm

[root@tecmint]# ls

conffiles  control  md5sums  postinst  postrm  prerm

There are lot more dtrx options to explore, just run the “dtrx –help” to list the available options.

[root@tecmint]# dtrx  --help

Usage: dtrx [options] archive [archive2 ...]

Intelligent archive extractor

Options:
  --version             	show program's version number and exit
  -h, --help            	show this help message and exit
  -l, -t, --list, --table      	list contents of archives on standard output
  -m, --metadata        	extract metadata from a .deb/.gem
  -r, --recursive       	extract archives contained in the ones listed
  -n, --noninteractive  	don't ask how to handle special cases
  -o, --overwrite       	overwrite any existing target output
  -f, --flat, --no-directory    extract everything to the current directory
  -v, --verbose         	be verbose/print debugging information
  -q, --quiet           	suppress warning/error messages

Reference Links

dtrx Homepage

I think you must give a try to dtrx, because it’s the only powerful command line tool that gives a single command to decompress any format of archive files.

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The two utilities for adding or creating user accounts in Unix/Linux systems are adduser and useradd. These commands are designed to add a single user account in the system at a time. What if you have multiple users accounts to be created? That’s when you need a program such as newusers.

Newusers is a useful command line utility used to update and create new user accounts at a single time. It is intended to be used in IT environments with large systems where a system administrator needed to update or create multiple user accounts in batch. It reads information from stdin (by default) or a file to update a set of existing user accounts or to create new users.

In this article, we will explain how to create multiple user accounts in batch mode using Newusers utility in Linux systems.

To create users in a batch, you can provide their information in a file in the following format, same as the standard password file:

pw_name:pw_passwd:pw_uid:pw_gid:pw_gecos:pw_dir:pw_shell

/bash

Save the file and set the required permissions on it.

$ sudo chmod 0600 users.txt 

Now run the newusers command with the input file to add the above user accounts at once.

$ sudo newusers users.txt

First, newusers program tries to create or update the specified accounts, and then write these changes to the user or group databases. In case of any errors except in the final writes to the databases, no changes are committed to the databases. This is simply how the newusers command works.

If the previous command is successful, check the /etc/passwd and /etc/groups files to confirm that the user accounts have been added as shown.

$ cat /etc/passwd | grep -E "ravi|tecmint"

For more information, see the newuser man page.

$ man newuser 

You might also like to check these following related articles.

1. 3 Ways to Change a Users Default Shell in Linux
2. How to Create a Shared Directory for All Users in Linux
3. Whowatch – Monitor Linux Users and Processes in Real Time
4. How to Send a Message to Logged Users in Linux

In this article, we’ve explained how to create multiple users in Linux using newusers program. Use the feedback form below to ask any questions or share your comments with us. If you know of any similar utilities out there, let us know as well.

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sudo is a powerful command line tool that enables a “permitted user” to run a command as another user (the superuser by default), as defined by a security policy. On most if not all Linux systems, the security policy is driven by the /etc/sudoers file.

Read Also: 10 Useful Sudoers Configurations for Setting ‘sudo’ in Linux

Therefore, to run a shell script or program as root, you need to use sudo command. However, sudo only recognizes and runs commands that exist in directories specified in the secure_path in the /etc/sudoers, unless a command is present in the secure_path, you’ll counter an error such as the one below.

This will happen even if the script exists in a directory in the PATH environmental variable, because when a user invokes sudo, PATH is replaced with secure_path.

$ echo  $PATH
$ ls  -l
$ sudo proconport.sh 80

$ sudo visudo

$ sudo ./proconport.sh 80

A port is a logical entity which acts as a endpoint of communication associated with an application or process on an Linux operating system. It is useful to know which ports are open and running services on a target machine before using them.

We can easily list open ports in Linux on a local machine using the netstat or several other Linux commands such NMAP.

In this guide, we will show you how to determine if ports on a remote host are reachable/open using simple netcat (in short nc) command.

netcat (or nc in short) is a powerful and easy-to-use utility that can be employed for just about anything in Linux in relation to TCP, UDP, or UNIX-domain sockets.

# yum install nc                  [On CentOS/RHEL]
# dnf install nc                  [On Fedora 22+]
$ sudo apt-get install netcat     [On Debian/Ubuntu]

We can use it to: open TCP connections, listen on arbitrary TCP and UDP ports, send UDP packets, do port scanning under both IPv4 and IPv6 and beyond.

Using netcat, you can check if a single or multiple or a range of open ports as follows. The command below will help us see if the port 22 is open on the host 192.168.56.10:

$ nc -zv 192.168.1.15 22

In the command above, the flag:

1. -z – sets nc to simply scan for listening daemons, without actually sending any data to them.
2. -v – enables verbose mode.

The next command will check if ports 80, 22 and 21 are open on the remote host 192.168.5.10 (we can use the hostname as well):
nc -zv 192.168.56.10 80 22 21

It is also possible to specify a range of ports to be scanned:’

$ nc -zv 192.168.56.10 20-80

For more examples and usage of netcat command, read through our articles as follows.

1. Transfer Files Between Linux Servers Using netcat Command
2. Linux Network Configuration and Troubleshooting Commands

That’s all. In this article, we explained how to check if ports on a remote host are reachable/open using simple netcat commands.

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In computer networking, an IP (Internet Protocol) address is a numerical identifier assigned permanently or temporarily to every device connected to a network that uses the Internet Protocol for communication. Its two major functions are to identify a network or host on a network and also serve for location addressing.

Read Also: How to Set Static IP Address and Configure Network in Linux

There are currently two versions of IP addresses: IPv4 and IPv6, which can either be private (viewable within an internal network) or public (can be seen by other machines on the Internet).

Additionally, a host can be assigned a static or dynamic IP address depending on the network configurations. In this article, we will show you 4 ways to find your Linux machine or server public IP address from the terminal in Linux.

1. Using dig Utility

dig (domain information groper) is a simple command line utility for probing DNS name servers. To find your public IP addresses, use the opendns.com resolver as in the command below:

$ dig +short myip.opendns.com @resolver1.opendns.com

120.88.41.175

2. Using host Utility

host command is an easy-to-use command line utility for carrying out DNS lookups. The command below will help to display your systems public IP address.

$ host myip.opendns.com resolver1.opendns.com | grep "myip.opendns.com has" | awk '{print $4}'

120.88.41.175

Important: The next two methods employ third party websites to display your IP address on the command line as described below.

3. Using wget Command Line Downloader

wget is a powerful command line downloader that supports various protocols like HTTP, HTTPS, FTP and many more. You can use it with third party websites to view your public IP address as follows:

$ wget -qO- http://ipecho.net/plain | xargs echo
$ wget -qO - icanhazip.com

120.88.41.175

4. Using cURL Command Line Downloader

curl is a popular command line tool for uploading or downloading files from a server using any of the supported protocols (HTTP, HTTPS, FILE, FTP, FTPS and others). The following commands displays your public IP address.

$ curl ifconfig.co
$ curl ifconfig.me
$ curl icanhazip.com

120.88.41.175

That’s It! You may find these following articles useful to read.

1. 5 Linux Command Line Based Tools for Downloading Files and Browsing Websites
2. 11 Ways to Find User Account Info and Login Details in Linux
3. 7 Ways to Determine the File System Type in Linux (Ext2, Ext3 or Ext4)

That’s all! If you have any questions or other methods to share in relation to this topic, use the feedback form below to write back to us.

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