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.

Source

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.

Source

There are a countless number of commands in Linux. We are bound to use a number of them on a daily routine or numerous times to perform common tasks than others. It is important to note that certain commands are “distro-based” – they can only be found in specific distros. While others are generic Unix/Linux commands that you’ll find in all if not most mainstream distros.

In this article, we will introduce you a list of most frequently used Linux commands with their examples for easy learning. You can find the actual description of each Linux command in their manual page which you can access like this:

$ man command-name

adduser/addgroup Command

The adduser and addgroup commands are used to add a user and group to the system respectively according to the default configuration specified in /etc/adduser.conf file.

$ sudo adduser tecmint

For more adduser and addgroup commands: 15 Practical Examples on adduser Command in Linux

agetty Command

agetty is a program which manages physical or virtual terminals and is invoked by init. Once it detects a connection, it opens a tty port, asks for a user’s login name and calls up the /bin/login command. Agetty is a substitute of Linux getty:

$ agetty -L 9600 ttyS1 vt100

alias Command

alias is a useful shell built-in command for creating aliases (shortcut) to a Linux command on a system. It is helpful for creating new/custom commands from existing Shell/Linux commands (including options):

$ alias home='cd /home/tecmint/public_html'

The above command will create an alias called home for /home/tecmint/public_html directory, so whenever you type home in the terminal prompt, it will put you in the /home/tecmint/public_html directory.

anacron Command

anacron is a Linux facility used to run commands periodically with a frequency defined in days, weeks and months.

Unlike its sister cron; it assumes that a system will not run continuously, therefore if a scheduled job is due when the system is off, it’s run once the machine is powered on.

$ apropos adduser

$ sudo apt update

$ sudo apt-get update

$ sudo aptitude update

$ arch 

$ sudo arp-scan --interface=enp2s0 --localnet  

$ sudo echo "shutdown -h now" | at -m 23:55

$ atq

$ atrm 2

$ awk '//{print}'/etc/hosts

$ basename bin/findhosts.sh

$ echo 20.05 + 15.00 | bc

$ tar -czf home.tar.gz .
$ bg 
$ jobs

$ bzip2 -z filename      #Compress
$ bzip2 -d filename.bz2  #Decompress

$ cal

$ cat file.txt

$ chgrp tecmint users.txt

$ chmod +x sysinfo.sh

$ chmod -R www-data:www-data /var/www/html

$ cksum README.txt

$ clear

$ cmp file1 file2

$ comm file1 file2

$ cp /home/tecmint/file1 /home/tecmint/Personal/

$ date
$ date --set="8 JUN 2017 13:00:00"

$ dd if=/home/tecmint/kali-linux-1.0.4-i386.iso of=/dev/sdc1 bs=512M; sync

$ df -h

$ diff file1 file2

$ dir

$ sudo dmidecode --type system

$ du /home/aaronkilik

$ echo “This is TecMint - Linux How Tos”

$ eject /dev/cdrom
$ eject /mnt/cdrom/
$ eject /dev/sda

$ env

$ exit

$ expr 20 + 30

$ factor 10

$ find /home/tecmint/ -name tecmint.txt

$ free -h 

$ grep ‘tecmint’ domain-list.txt

$ groups
$ groups tecmint

$ gzip passwds.txt
$ cat file1 file2 | gzip > foo.gz

$ gunzip foo.gz

# ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head 

$ history

$ hostname
$ hostname NEW_HOSTNAME

$ hostnamectl
$ sudo hostnamectl set-hostname NEW_HOSTNAME

$ sudo hwclock
$ sudo hwclock --set --date 8/06/2017

$ hwinfo

$ id tecmint

$ ifconfig
$ sudo ifconfig eth0 up
$ sudo ifconfig eth0 down
$ sudo ifconfig eth0 172.16.25.125

$ ionice -c 3 rm /var/logs/syslog

$ iostat 

$ sudo ip addr add 192.168.56.10 dev eth1

$ sudo iptables -L -n -v

$ iw list 

$ iwlist wlp1s0 scanning

$ kill -p 2300
$ kill -SIGTERM -p 2300

$ killall firefox

$ kmod list

$ last 

$ ln -s /usr/bin/lscpu cpuinfo

$ locate -b '\domain-list.txt'

$ sudo login

$ ls -l file1

$ sudo lshw  

$ lscpu

$ lsof -u tecmint

$ lsusb 

$ man du
$ man df

$ sudo debsums

$ mkdir tecmint-files
OR 
$ mkdir -p tecmint-files

$ more file.txt

$ mv test.sh sysinfo.sh 

$ nano file.txt

$ nc -zv 192.168.1.5 22

$ netstat -a | more

$ nice -12 tar -czf backup.tar.bz2 /home/*

$ nmap -sV 192.168.56.0/24

$ nproc  

$ tar -czf - * | openssl enc -e -aes256 -out backup.tar.gz

$ passwd tecmint

$ pidof init
$ pidof cinnamon

$ ping google.com

# ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head

$ pstree

$ pwd

$ sudo rdiff-backup /etc /media/tecmint/Backup/server_etc.backup

$ reboot

$ rename 's/\.html$/\.php/' *.html

$ rm file1
$ rm -rf my-files

$ rmdir /backup/all

$ scp ~/names.txt root@192.168.56.10:/root/names.txt

$ shutdown --poweroff

$ check.sh; sleep 5; sudo apt update

$ cat words.txt

$ tar -cvjf backup.tar.bz2 /home/tecmint/Documents/* 

$ ssh tecmint@192.168.56.10

$ stat file1

$ su 
$ su tecmint

$ sudo apt update
$ sudo useradd tecmint
$ sudo passwd tecmint

$ sum output file.txt 

$tac file.txt

$ tail long-file
OR
$ tail -n 15 long-file

$ talk person [ttyname]
OR
$ talk‘user@host’ [ttyname]

$ tar -czf home.tar.gz .

$ echo "Testing how tee command works" | tee file1 

$ time wc /etc/hosts

$ top

$ touch file.txt

$ cat domain-list.txt | tr [:lower:] [:upper:]

$ uname 

$ cat domain-list.txt

$ uptime

$ users

$ vim file

$ w

$ wall “This is TecMint – Linux How Tos”

$ watch -d ls -l

$ wc filename

$ wget -c http://ftp.gnu.org/gnu/wget/wget-1.5.3.tar.gz

$ whatis wget

$ which who

$ who

$ whereis cat

$ echo /home/aaronkilik/test/ /home/aaronkilik/tmp | xargs -n 1 cp -v /home/aaronkilik/bin/sys_info.sh

$ yes "This is TecMint - Linux HowTos"

$ youtube-dl --list-formats https://www.youtube.com/watch?v=iR

$ zcmp domain-list.txt.zip basic_passwords.txt.zip
$ zdiff domain-list.txt.zip basic_passwords.txt.zip 

$ tar cf - . | zip | dd of=/dev/nrst0 obs=16k
$ zip inarchive.zip foo.c bar.c --out outarchive.zip
$ tar cf - .| zip backup -

$ zz

Sort is a Linux program used for printing lines of input text files and concatenation of all files in sorted order. Sort command takes blank space as field separator and entire Input file as sort key. It is important to notice that sort command don’t actually sort the files but only print the sorted output, until your redirect the output.

This article aims at deep insight of Linux ‘sort‘ command with 14 useful practical examples that will show you how to use sort command in Linux.

1. First we will be creating a text file (tecmint.txt) to execute ‘sort‘ command examples. Our working directory is ‘/home/$USER/Desktop/tecmint.

The option ‘-e‘ in the below command enables interpretion of backslash and /n tells echo to write each string to a new line.

$ echo -e "computer\nmouse\nLAPTOP\ndata\nRedHat\nlaptop\ndebian\nlaptop" > tecmint.txt

2. Before we start with ‘sort‘ lets have a look at the contents of the file and the way it look.

$ cat tecmint.txt

3. Now sort the content of the file using following command.

$ sort tecmint.txt

Note: The above command don’t actually sort the contents of text file but only show the sorted output on terminal.

4. Sort the contents of the file ‘tecmint.txt‘ and write it to a file called (sorted.txt) and verify the content by using cat command.

$ sort tecmint.txt > sorted.txt
$ cat sorted.txt

5. Now sort the contents of text file ‘tecmint.txt‘ in reverse order by using ‘-r‘ switch and redirect output to a file ‘reversesorted.txt‘. Also check the content listing of the newly created file.

$ sort -r tecmint.txt > reversesorted.txt
$ cat reversesorted.txt

6. We are going a create a new file (lsl.txt) at the same location for detailed examples and populate it using the output of ‘ls -l‘ for your home directory.

$ ls -l /home/$USER > /home/$USER/Desktop/tecmint/lsl.txt
$ cat lsl.txt

Now will see examples to sort the contents on the basis of other field and not the default initial characters.

7. Sort the contents of file ‘lsl.txt‘ on the basis of 2nd column (which represents number of symbolic links).

$ sort -nk2 lsl.txt

Note: The ‘-n‘ option in the above example sort the contents numerically. Option ‘-n‘ must be used when we wanted to sort a file on the basis of a column which contains numerical values.

8. Sort the contents of file ‘lsl.txt‘ on the basis of 9th column (which is the name of the files and folders and is non-numeric).

$ sort -k9 lsl.txt

9. It is not always essential to run sort command on a file. We can pipeline it directly on the terminal with actual command.

$ ls -l /home/$USER | sort -nk5

10. Sort and remove duplicates from the text file tecmint.txt. Check if the duplicate has been removed or not.

$ cat tecmint.txt
$ sort -u tecmint.txt

Rules so far (what we have observed):

1. Lines starting with numbers are preferred in the list and lies at the top until otherwise specified (-r).
2. Lines starting with lowercase letters are preferred in the list and lies at the top until otherwise specified (-r).
3. Contents are listed on the basis of occurrence of alphabets in dictionary until otherwise specified (-r).
4. Sort command by default treat each line as string and then sort it depending upon dictionary occurrence of alphabets (Numeric preferred; see rule – 1) until otherwise specified.

11. Create a third file ‘lsla.txt‘ at the current location and populate it with the output of ‘ls -lA‘ command.

$ ls -lA /home/$USER > /home/$USER/Desktop/tecmint/lsla.txt
$ cat lsla.txt

Those having understanding of ‘ls‘ command knows that ‘ls -lA’=’ls -l‘ + Hidden files. So most of the contents on these two files would be same.

12. Sort the contents of two files on standard output in one go.

$ sort lsl.txt lsla.txt

Notice the repetition of files and folders.

13. Now we can see how to sort, merge and remove duplicates from these two files.

$ sort -u lsl.txt lsla.txt

Notice that duplicates has been omitted from the output. Also, you can write the output to a new file by redirecting the output to a file.

14. We may also sort the contents of a file or the output based upon more than one column. Sort the output of ‘ls -l‘ command on the basis of field 2,5 (Numeric) and 9 (Non-Numeric).

$ ls -l /home/$USER | sort -t "," -nk2,5 -k9

That’s all for now. In the next article we will cover a few more examples of ‘sort‘ command in detail for you. Till then stay tuned and connected to Tecmint. Keep sharing. Keep commenting. Like and share us and help us get spread.

Source

One of the critical areas under Linux performance monitoring has to be CPU usage and system load. There are several Linux performance monitoring tools to keep an eye on how things are unfolding on a system.

A number of these tools simply output the system state/statistics while a few others provide you means of managing system performance. One such tool called CPUTool.

CPUTool is a simple yet powerful command-line tool for limiting and controlling CPU utilization of any process to a given limit and allows the interruption of process execution if the system load overreach a defined threshold.

How Does CPUTool Work?

In order to limit CPU usage, cputool sends the SIGSTOP and SIGCONT signals to processes and this is determined by the system load. It relies on the /proc pseudo-filesystem to read PIDs and their CPU usage measures.

It may be used to limit the CPU usage or system load influenced by a single process or a group of processes to a given limit and/or suspend processes if the system load goes beyond a threshold.

Suggested Read: Understand Linux Load Averages and Monitor Performance of Linux

Install CPUTool to Limit CPU Usage and Load Average

A CPUTool is only available to install on Debian/Ubuntu and its derivatives from the default system repositories using package management tool.

$ sudo apt install cputool

Limiting Process CPU Usage With CUPTool

Now lets look at how cputool really works. To demonstrate it all, we will run a dd command which should result into a high CPU percentage, in the background and display its PID.

# dd if=/dev/zero of=/dev/null &

To monitor CPU usage we can use the top or glances tools that allow us to view a real-time regularly updated state of a running Linux system processes:

# top

Monitor dd Command CPU Usage

From the output above, we can see that dd command is having the highest percentage of CPU time 99.7%)Now we can limit this using cputool as shown below.

The --cpu-limit or -c flag is used to set a usage percentage for a process or group of processes and -p to specify a PID. The following command will limit the dd command (PID 8275) to 50% use of one CPU core:

# cputool --cpu-limit 50 -p 8275 

After running cputool, we can check the new CPU usage for the process (PID 8275) once more. Now the CPU usage for dd process should range from (49.0%-52.0%).

# top

Limit Process CPU to 50% Usage

To further limit dd’s CPU usage to 20%, we can run cputool for a second time:

# cputool --cpu-limit 20 -p 8275 

Then immediately check using tools such as top or glances like this (the CPU usage for dd should now range from 19.0%-22.0% or slightly beyond this):

# top

Limit Process CPU Usage to 20%

Note that the shell doesn’t expect any user input while cputool is running; therefore becomes unresponsive. To kill it (this will terminate the CPU usage limitation operation), press Ctrl + C.

Importantly, to specify a process group (one program with several running instances each with a distinct PID) for instance HTTP web server:

# pidof apache2
9592 3643 3642 3641 3640 3638 3637 1780

Use the -P flag like this:

# cputool --cpu-limit 20 -P 1780

Limiting System Load with CUPTool

The -l option is used to specify the maximum load the system may go though for the process or process group to continue running. We may use a fractional value (e.g. 2.5).

The example below means run rsync for a local backup only when the system load does not exceed 3.5:

# cputool --load-limit 3.5 --rsync -av /home/tecmint /backup/`date +%Y-%m-%d`/

For more information and usage, view the CPUTool man page:

# man cputool

Do check out following useful guides for finding CPU info and CPU performance monitoring:

1. 9 Useful Commands to Get CPU Information on Linux
2. Cpustat – Monitors CPU Utilization by Running Processes in Linux
3. CoreFreq – A Powerful CPU Monitoring Tool for Linux Systems
4. Find Top Running Processes by Highest Memory and CPU Usage in Linux

In conclusion, CPUTool really comes in handy for Linux performance management.

 
Source

Thanks for all the likes, good words and support you gave us in the first two part of this article. In the first article we discussed commands for those users who have just switched to Linux and needed the necessary knowledge to start with.

1. 20 Useful Commands for Linux Newbies

In the second article we discussed the commands which a middle level user requires to manage his own system.

1. 20 Advanced Commands for Middle Level Linux Users

What Next? In this article I will be explaining those commands required for administrating the Linux Server.

41. Command: ifconfig

ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usually only needed when debugging or when system tuning is needed.

Check Active Network Interfaces

[avishek@tecmint ~]$ ifconfig 

eth0      Link encap:Ethernet  HWaddr 40:2C:F4:EA:CF:0E  
          inet addr:192.168.1.3  Bcast:192.168.1.255  Mask:255.255.255.0 
          inet6 addr: fe80::422c:f4ff:feea:cf0e/64 Scope:Link 
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1 
          RX packets:163843 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:124990 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:1000 
          RX bytes:154389832 (147.2 MiB)  TX bytes:65085817 (62.0 MiB) 
          Interrupt:20 Memory:f7100000-f7120000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0 
          inet6 addr: ::1/128 Scope:Host 
          UP LOOPBACK RUNNING  MTU:16436  Metric:1 
          RX packets:78 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:78 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:0 
          RX bytes:4186 (4.0 KiB)  TX bytes:4186 (4.0 KiB)

Check All Network Interfaces

Display details of All interfaces including disabled interfaces using “-a” argument.

[avishek@tecmint ~]$ ifconfig -a

eth0      Link encap:Ethernet  HWaddr 40:2C:F4:EA:CF:0E  
          inet addr:192.168.1.3  Bcast:192.168.1.255  Mask:255.255.255.0 
          inet6 addr: fe80::422c:f4ff:feea:cf0e/64 Scope:Link 
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1 
          RX packets:163843 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:124990 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:1000 
          RX bytes:154389832 (147.2 MiB)  TX bytes:65085817 (62.0 MiB) 
          Interrupt:20 Memory:f7100000-f7120000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0 
          inet6 addr: ::1/128 Scope:Host 
          UP LOOPBACK RUNNING  MTU:16436  Metric:1 
          RX packets:78 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:78 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:0 
          RX bytes:4186 (4.0 KiB)  TX bytes:4186 (4.0 KiB) 

virbr0    Link encap:Ethernet  HWaddr 0e:30:a3:3a:bf:03  
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

Disable an Interface

[avishek@tecmint ~]$ ifconfig eth0 down

Enable an Interface

[avishek@tecmint ~]$ ifconfig eth0 up

Assign IP Address to an Interface

Assign “192.168.1.12” as the IP address for the interface eth0.

[avishek@tecmint ~]$ ifconfig eth0 192.168.1.12

Change Subnet Mask of Interface eth0

[avishek@tecmint ~]$ ifconfig eth0 netmask 255.255.255.

Change Broadcast Address of Interface eth0

[avishek@tecmint ~]$ ifconfig eth0 broadcast 192.168.1.255

Assign IP Address, Netmask and Broadcast to Interface eth0

[avishek@tecmint ~]$ ifconfig eth0 192.168.1.12 netmask 255.255.255.0 broadcast 192.168.1.255

Note: If using a wireless network you need to use command “iwconfig“. For more “ifconfig” command examples and usage, read 15 Useful “ifconfig” Commands.

42. Command: netstat

netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc..,

List All Network Ports

[avishek@tecmint ~]$ netstat -a

Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     741379   /run/user/user1/keyring-I5cn1c/gpg
unix  2      [ ACC ]     STREAM     LISTENING     8965     /var/run/acpid.socket
unix  2      [ ACC ]     STREAM     LISTENING     18584    /tmp/.X11-unix/X0
unix  2      [ ACC ]     STREAM     LISTENING     741385   /run/user/user1/keyring-I5cn1c/ssh
unix  2      [ ACC ]     STREAM     LISTENING     741387   /run/user/user1/keyring-I5cn1c/pkcs11
unix  2      [ ACC ]     STREAM     LISTENING     20242    @/tmp/dbus-ghtTjuPN46
unix  2      [ ACC ]     STREAM     LISTENING     13332    /var/run/samba/winbindd_privileged/pipe
unix  2      [ ACC ]     STREAM     LISTENING     13331    /tmp/.winbindd/pipe
unix  2      [ ACC ]     STREAM     LISTENING     11030    /var/run/mysqld/mysqld.sock
unix  2      [ ACC ]     STREAM     LISTENING     19308    /tmp/ssh-qnZadSgJAbqd/agent.3221
unix  2      [ ACC ]     STREAM     LISTENING     436781   /tmp/HotShots
unix  2      [ ACC ]     STREAM     LISTENING     46110    /run/user/ravisaive/pulse/native
unix  2      [ ACC ]     STREAM     LISTENING     19310    /tmp/gpg-zfE9YT/S.gpg-agent
....

List All TCP Ports

[avishek@tecmint ~]$ netstat -at

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 localhost:mysql         *:*                     LISTEN     
tcp        0      0 *:5901                  *:*                     LISTEN     
tcp        0      0 *:5902                  *:*                     LISTEN     
tcp        0      0 *:x11-1                 *:*                     LISTEN     
tcp        0      0 *:x11-2                 *:*                     LISTEN     
tcp        0      0 *:5938                  *:*                     LISTEN     
tcp        0      0 localhost:5940          *:*                     LISTEN     
tcp        0      0 ravisaive-OptiPl:domain *:*                     LISTEN     
tcp        0      0 ravisaive-OptiPl:domain *:*                     LISTEN     
tcp        0      0 localhost:ipp           *:*                     LISTEN     
tcp        0      0 ravisaive-OptiPle:48270 ec2-23-21-236-70.c:http ESTABLISHED
tcp        0      0 ravisaive-OptiPle:48272 ec2-23-21-236-70.c:http TIME_WAIT  
tcp        0      0 ravisaive-OptiPle:48421 bom03s01-in-f22.1:https ESTABLISHED
tcp        0      0 ravisaive-OptiPle:48269 ec2-23-21-236-70.c:http ESTABLISHED
tcp        0      0 ravisaive-OptiPle:39084 channel-ecmp-06-f:https ESTABLISHED
...

Show Statistics for All Ports

[avishek@tecmint ~]$ netstat -s

Ip:
    4994239 total packets received
    0 forwarded
    0 incoming packets discarded
    4165741 incoming packets delivered
    3248924 requests sent out
    8 outgoing packets dropped
Icmp:
    29460 ICMP messages received
    566 input ICMP message failed.
    ICMP input histogram:
        destination unreachable: 98
        redirects: 29362
    2918 ICMP messages sent
    0 ICMP messages failed
    ICMP output histogram:
        destination unreachable: 2918
IcmpMsg:
        InType3: 98
        InType5: 29362
        OutType3: 2918
Tcp:
    94533 active connections openings
    23 passive connection openings
    5870 failed connection attempts
    7194 connection resets received
....

OK! For some reason if you want not to resolve host, port and user name as a output of netstat.

[avishek@tecmint ~]$ netstat -an

Fine, you may need to get the output of netstat continuously till interrupt instruction is passed (ctrl+c).

[avishek@tecmint ~]$ netstat -c

For more “netstat” command examples and usage, see the article 20 Netstat Command Examples.

43. Command: nslookup

A network utility program used to obtain information about Internet servers. As its name suggests, the utility finds name server information for domains by querying DNS.

[avishek@tecmint ~]$ nslookup tecmint.com 

Server:		192.168.1.1 
Address:	192.168.1.1#53 

Non-authoritative answer: 
Name:	tecmint.com 
Address: 50.16.67.239

Query Mail Exchanger Record

[avishek@tecmint ~]$ nslookup -query=mx tecmint.com 

Server:		192.168.1.1 
Address:	192.168.1.1#53 

Non-authoritative answer: 
tecmint.com	mail exchanger = 0 smtp.secureserver.net. 
tecmint.com	mail exchanger = 10 mailstore1.secureserver.net. 

Authoritative answers can be found from:

Query Name Server

[avishek@tecmint ~]$ nslookup -type=ns tecmint.com 

Server:		192.168.1.1 
Address:	192.168.1.1#53 

Non-authoritative answer: 
tecmint.com	nameserver = ns3404.com. 
tecmint.com	nameserver = ns3403.com. 

Authoritative answers can be found from:

Query DNS Record

[avishek@tecmint ~]$ nslookup -type=any tecmint.com 

Server:		192.168.1.1 
Address:	192.168.1.1#53 

Non-authoritative answer: 
tecmint.com	mail exchanger = 10 mailstore1.secureserver.net. 
tecmint.com	mail exchanger = 0 smtp.secureserver.net. 
tecmint.com	nameserver = ns06.domaincontrol.com. 
tecmint.com	nameserver = ns3404.com. 
tecmint.com	nameserver = ns3403.com. 
tecmint.com	nameserver = ns05.domaincontrol.com. 

Authoritative answers can be found from:

Query Start of Authority

[avishek@tecmint ~]$ nslookup -type=soa tecmint.com 

Server:		192.168.1.1 
Address:	192.168.1.1#53 

Non-authoritative answer: 
tecmint.com 
	origin = ns3403.hostgator.com 
	mail addr = dnsadmin.gator1702.hostgator.com 
	serial = 2012081102 
	refresh = 86400 
	retry = 7200 
	expire = 3600000 
	minimum = 86400 

Authoritative answers can be found from:

Query Port Number

Change the port number using which you want to connect

[avishek@tecmint ~]$ nslookup -port 56 tecmint.com

Server:		tecmint.com
Address:	50.16.76.239#53

Name:	56
Address: 14.13.253.12

Read Also : 8 Nslookup Commands

44. Command: dig

dig is a tool for querying DNS nameservers for information about host addresses, mail exchanges, nameservers, and related information. This tool can be used from any Linux (Unix) or Macintosh OS X operating system. The most typical use of dig is to simply query a single host.

[avishek@tecmint ~]$ dig tecmint.com

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<

Turn Off Comment Lines

[avishek@tecmint ~]$ dig tecmint.com +nocomments 

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +nocomments 
;; global options: +cmd 
;tecmint.com.			IN	A 
tecmint.com.		14400	IN	A	40.216.66.239 
;; Query time: 418 msec 
;; SERVER: 192.168.1.1#53(192.168.1.1) 
;; WHEN: Sat Jun 29 13:53:22 2013 
;; MSG SIZE  rcvd: 45

Turn Off Authority Section

[avishek@tecmint ~]$ dig tecmint.com +noauthority 

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +noauthority 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<

Turn Off Additional Section

[avishek@tecmint ~]$ dig  tecmint.com +noadditional 

; <<>> DiG 9.9.2-P1 <<>> tecmint.com +noadditional
;; global options: +cmd
;; Got answer:
;; ->>HEADER<

Turn Off Stats Section

[avishek@tecmint ~]$ dig tecmint.com +nostats 

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +nostats 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<

Turn Off Answer Section

[avishek@tecmint ~]$ dig tecmint.com +noanswer 

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +noanswer 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<

Disable All Section at Once

[avishek@tecmint ~]$ dig tecmint.com +noall 

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +noall 
;; global options: +cmd

Read Also : 10 Linux Dig Command Examples

45. Command: uptime

You have just connected to your Linux Server Machine and founds Something unusual or malicious, what you will do? Guessing…. NO, definitely not you could run uptime to verify what happened actually when the server was unattended.

[avishek@tecmint ~]$ uptime

14:37:10 up  4:21,  2 users,  load average: 0.00, 0.00, 0.04

46. Command: wall

one of the most important command for administrator, wall sends a message to everybody logged in with their mesg permission set to “yes“. The message can be given as an argument to wall, or it can be sent to wall’s standard input.

[avishek@tecmint ~]$ wall "we will be going down for maintenance for one hour sharply at 03:30 pm"

Broadcast message from root@localhost.localdomain (pts/0) (Sat Jun 29 14:44:02 2013): 

we will be going down for maintenance for one hour sharply at 03:30 pm

47. command: mesg

Lets you control if people can use the “write” command, to send text to you over the screen.

mesg [n|y]
n - prevents the message from others popping up on the screen.
y – Allows messages to appear on your screen.

48. Command: write

Let you send text directly to the screen of another Linux machine if ‘mesg’ is ‘y’.

[avishek@tecmint ~]$ write ravisaive

49. Command: talk

An enhancement to write command, talk command lets you talk to the logged in users.

[avishek@tecmint ~]$ talk ravisaive

Note: If talk command is not installed, you can always apt or yum the required packages.

[avishek@tecmint ~]$ yum install talk
OR
[avishek@tecmint ~]$ apt-get install talk

50. Command: w

what command ‘w’ seems you funny? But actually it is not. t’s a command, even if it’s just one letter long! The command “w” is a combination of uptime and who commands given one immediately after the other, in that order.

[avishek@tecmint ~]$ w

15:05:42 up  4:49,  3 users,  load average: 0.02, 0.01, 0.00 
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT 
server   tty7     :0               14:06    4:43m  1:42   0.08s pam: gdm-passwo 
server   pts/0    :0.0             14:18    0.00s  0.23s  1.65s gnome-terminal 
server   pts/1    :0.0             14:47    4:43   0.01s  0.01s bash

51. Command: rename

As the name suggests, this command rename files. rename will rename the specified files by replacing the first occurrence from the file name.

Give the file names a1, a2, a3, a4.....1213

Just type the command.

 rename a1 a0 a?
 rename a1 a0 a??

52. Command: top

Displays the processes of CPU. This command refresh automatically, by default and continues to show CPUprocesses unless interrupt-instruction is given.

[avishek@tecmint ~]$ top

top - 14:06:45 up 10 days, 20:57,  2 users,  load average: 0.10, 0.16, 0.21
Tasks: 240 total,   1 running, 235 sleeping,   0 stopped,   4 zombie
%Cpu(s):  2.0 us,  0.5 sy,  0.0 ni, 97.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   2028240 total,  1777848 used,   250392 free,    81804 buffers
KiB Swap:  3905532 total,   156748 used,  3748784 free,   381456 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+ COMMAND                                                                                                            
23768 ravisaiv  20   0 1428m 571m  41m S   2.3 28.9  14:27.52 firefox                                                                                                            
24182 ravisaiv  20   0  511m 132m  25m S   1.7  6.7   2:45.94 plugin-containe                                                                                                    
26929 ravisaiv  20   0  5344 1432  972 R   0.7  0.1   0:00.07 top                                                                                                                
24875 ravisaiv  20   0  263m  14m  10m S   0.3  0.7   0:02.76 lxterminal                                                                                                         
    1 root      20   0  3896 1928 1228 S   0.0  0.1   0:01.62 init                                                                                                               
    2 root      20   0     0    0    0 S   0.0  0.0   0:00.06 kthreadd                                                                                                           
    3 root      20   0     0    0    0 S   0.0  0.0   0:17.28 ksoftirqd/0                                                                                                        
    5 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kworker/0:0H                                                                                                       
    7 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kworker/u:0H                                                                                                       
    8 root      rt   0     0    0    0 S   0.0  0.0   0:00.12 migration/0                                                                                                        
    9 root      20   0     0    0    0 S   0.0  0.0   0:00.00 rcu_bh                                                                                                             
   10 root      20   0     0    0    0 S   0.0  0.0   0:26.94 rcu_sched                                                                                                          
   11 root      rt   0     0    0    0 S   0.0  0.0   0:01.95 watchdog/0                                                                                                         
   12 root      rt   0     0    0    0 S   0.0  0.0   0:02.00 watchdog/1                                                                                                         
   13 root      20   0     0    0    0 S   0.0  0.0   0:17.80 ksoftirqd/1                                                                                                        
   14 root      rt   0     0    0    0 S   0.0  0.0   0:00.12 migration/1                                                                                                        
   16 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kworker/1:0H                                                                                                       
   17 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 cpuset                                                                                                             
   18 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 khelper                                                                                                            
   19 root      20   0     0    0    0 S   0.0  0.0   0:00.00 kdevtmpfs                                                                                                          
   20 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 netns                                                                                                              
   21 root      20   0     0    0    0 S   0.0  0.0   0:00.04 bdi-default                                                                                                        
   22 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kintegrityd                                                                                                        
   23 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kblockd                                                                                                            
   24 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 ata_sff

Read Also : 12 TOP Command Examples

53. Command: mkfs.ext4

This command create a new ext4 file system on the specified device, if wrong device is followed after this command, the whole block will be wiped and formatted, hence it is suggested not to run this command unless and until you understand what you are doing.

Mkfs.ext4 /dev/sda1 (sda1 block will be formatted)
mkfs.ext4 /dev/sdb1 (sdb1 block will be formatted)

Read More: What is Ext4 and How to Create and Convert

54. Command: vi/emacs/nano

vi (visual), emacs, nano are some of the most commonly used editors in Linux. They are used oftenly to edit text, configuration,… files. A quick guide to work around vi and nano is, emacs is a.

vi-editor

[avishek@tecmint ~]$ touch a.txt (creates a text file a.txt) 
[avishek@tecmint ~]$ vi a.txt (open a.txt with vi editor)

[press ‘i’ to enter insert mode, or you won’t be able to type-in anything]

echo "Hello"  (your text here for the file)

1. alt+x (exit insert mode, remember to keep some space between the last letter.
2. ctrl+x command or your last word will be deleted).
3. :wq! (saves the file, with the current text, remember ‘!’ is to override).

nano editor

[avishek@tecmint ~]$ nano a.txt (open a.txt file to be edited with nano)

edit, with the content, required

ctrl +x (to close the editor). It will show output as:

Save modified buffer (ANSWERING "No" WILL DESTROY CHANGES) ?                    
 Y Yes 
 N No           ^C Cancel

Click ‘y’ to yes and enter file name, and you are done.

55. Command: rsync

Rsync copies files and has a -P switch for a progress bar. So if you have rsync installed, you could use a simple alias.

alias cp='rsync -aP'

Now try to copy a large file in terminal and see the output with remaining items, similar to a progress bar.

Moreover, Keeping and Maintaining backup is one of the most important and boring work a system administrator, needs to perform. Rsync is a very nice tool (there exists, several other) to create and maintain backup, in terminal.

[avishek@tecmint ~]$ rsync -zvr IMG_5267\ copy\=33\ copy\=ok.jpg ~/Desktop/ 

sending incremental file list 
IMG_5267 copy=33 copy=ok.jpg 

sent 2883830 bytes  received 31 bytes  5767722.00 bytes/sec 
total size is 2882771  speedup is 1.00

Note: -z for compression, -v for verbose and -r for recursive.

56. Command: free

Keeping track of memory and resources is as much important, as any other task performed by an administrator, and ‘free‘ command comes to rescue here.

Current Usage Status of Memory

[avishek@tecmint ~]$ free

             total       used       free     shared    buffers     cached
Mem:       2028240    1788272     239968          0      69468     363716
-/+ buffers/cache:    1355088     673152
Swap:      3905532     157076    3748456

Tuned Output in KB, or MB, or GB

[avishek@tecmint ~]$ free -b

             total       used       free     shared    buffers     cached
Mem:    2076917760 1838272512  238645248          0   71348224  372670464
-/+ buffers/cache: 1394253824  682663936
Swap:   3999264768  160845824 3838418944

[avishek@tecmint ~]$ free -k

             total       used       free     shared    buffers     cached
Mem:       2028240    1801484     226756          0      69948     363704
-/+ buffers/cache:    1367832     660408
Swap:      3905532     157076    3748456

[avishek@tecmint ~]$ free -m

             total       used       free     shared    buffers     cached
Mem:          1980       1762        218          0         68        355
-/+ buffers/cache:       1338        641
Swap:         3813        153       3660

[avishek@tecmint ~]$ free -g

             total       used       free     shared    buffers     cached
Mem:             1          1          0          0          0          0
-/+ buffers/cache:          1          0
Swap:            3          0          3

Check Current Usage in Human Readable Format

[avishek@tecmint ~]$ free -h

             total       used       free     shared    buffers     cached
Mem:          1.9G       1.7G       208M         0B        68M       355M
-/+ buffers/cache:       1.3G       632M
Swap:         3.7G       153M       3.6G

Check Status Contineously After Regular Interval

[avishek@tecmint ~]$ free -s 3

             total       used       free     shared    buffers     cached
Mem:       2028240    1824096     204144          0      70708     364180
-/+ buffers/cache:    1389208     639032
Swap:      3905532     157076    3748456

             total       used       free     shared    buffers     cached
Mem:       2028240    1824192     204048          0      70716     364212
-/+ buffers/cache:    1389264     638976
Swap:      3905532     157076    3748456

Read Also : 10 Examples of Free Command

57. Command: mysqldump

Ok till now you would have understood what this command actually stands for, from the name of this command.mysqldump commands dumps (backups) all or a particular database data into a given a file.For example,

[avishek@tecmint ~]$ mysqldump -u root -p --all-databases > /home/server/Desktop/backupfile.sql

Note: mysqldump requires mysql to be running and correct password for authorisation. We have covered some useful “mysqldump” commands at Database Backup with mysqldump Command

58. Command: mkpasswd

Make a hard-to-guess, random password of the length as specified.

[avishek@tecmint ~]$ mkpasswd -l 10

zI4+Ybqfx9

[avishek@tecmint ~]$ mkpasswd -l 20 

w0Pr7aqKk&hmbmqdrlmk

Note: -l 10 generates a random password of 10 characters while -l 20 generates a password of character 20, it could be set to anything to get desired result. This command is very useful and implemented in scripting language oftenly to generate random passwords. You might need to yum or apt the ‘expect’ package to use this command.

[root@tecmint ~]# yum install expect 
OR
[root@tecmint ~]# apt-get install expect

59. Command: paste

Merge two or more text files on lines using. Example. If the content of file1 was:

1 
2 
3 

and file2 was: 

a 
b 
c 
d 
the resulting file3 would be: 

1    a 
2    b 
3    c 
     d

60.Command: lsof

lsof stands for “list open files” and displays all the files that your system has currently opened. It’s very useful to figure out which processes uses a certain file, or to display all the files for a single process. Some useful 10 lsof Command examples, you might be interested in reading.

[avishek@tecmint ~]$ lsof 

COMMAND     PID   TID            USER   FD      TYPE     DEVICE SIZE/OFF       NODE NAME
init          1                  root  cwd       DIR        8,1     4096          2 /
init          1                  root  rtd       DIR        8,1     4096          2 /
init          1                  root  txt       REG        8,1   227432     395571 /sbin/init
init          1                  root  mem       REG        8,1    47080     263023 /lib/i386-linux-gnu/libnss_files-2.17.so
init          1                  root  mem       REG        8,1    42672     270178 /lib/i386-linux-gnu/libnss_nis-2.17.so
init          1                  root  mem       REG        8,1    87940     270187 /lib/i386-linux-gnu/libnsl-2.17.so
init          1                  root  mem       REG        8,1    30560     263021 /lib/i386-linux-gnu/libnss_compat-2.17.so
init          1                  root  mem       REG        8,1   124637     270176 /lib/i386-linux-gnu/libpthread-2.17.so
init          1                  root  mem       REG        8,1  1770984     266166 /lib/i386-linux-gnu/libc-2.17.so
init          1                  root  mem       REG        8,1    30696     262824 /lib/i386-linux-gnu/librt-2.17.so
init          1                  root  mem       REG        8,1    34392     262867 /lib/i386-linux-gnu/libjson.so.0.1.0
init          1                  root  mem       REG        8,1   296792     262889 /lib/i386-linux-gnu/libdbus-1.so.3.7.2
init          1                  root  mem       REG        8,1    34168     262840 /lib/i386-linux-gnu/libnih-dbus.so.1.0.0
init          1                  root  mem       REG        8,1    95616     262848 /lib/i386-linux-gnu/libnih.so.1.0.0
init          1                  root  mem       REG        8,1   134376     270186 /lib/i386-linux-gnu/ld-2.17.so
init          1                  root    0u      CHR        1,3      0t0       1035 /dev/null
init          1                  root    1u      CHR        1,3      0t0       1035 /dev/null
init          1                  root    2u      CHR        1,3      0t0       1035 /dev/null
init          1                  root    3r     FIFO        0,8      0t0       1714 pipe
init          1                  root    4w     FIFO        0,8      0t0       1714 pipe
init          1                  root    5r     0000        0,9        0       6245 anon_inode
init          1                  root    6r     0000        0,9        0       6245 anon_inode
init          1                  root    7u     unix 0xf5e91f80      0t0       8192 @/com/ubuntu/upstart
init          1                  root    8w      REG        8,1     3916        394 /var/log/upstart/teamviewerd.log.1 (deleted)

This is not the end, a System Administrator does a lot of stuff, to provide you such a nice interface, upon which you work. System Administration is actually an art of learning and implementing in a very much perfect way. We will try to get you with all other necessary stuff which a linux professional must learn, linux in its basic actually itself, is a process of learning and learning.

Source

Wget is a popular, non-interactive and widely used network downloader which supports protocols such as HTTP, HTTPS, and FTP, and retrieval via HTTP proxies. By default, wget downloads files in the current working directory where it is run.

Read Also: How to Rename File While Downloading with Wget in Linux

In this article, we will show how to download files to a specific directory without moving into that directory. This guide is useful, if, for example, you are using wget in a script, and want to automate downloads which should be stored in different directories.

In addition, wget being non-interactive (can work in the background) by design makes it easy to use for automating downloads via shell scripts. You can actually initiate a download and disconnect from the system, letting wget complete the job.

Wget’s -P or --directory-prefix option is used to set the directory prefix where all retrieved files and subdirectories will be saved to.

In this example, we will demonstrate how to download the glances config template and store it under /etc/glances/ directory.

$ sudo mkdir /etc/glances
$ ls /etc/glances/
$ sudo wget https://raw.githubusercontent.com/nicolargo/glances/develop/conf/glances.conf -P /etc/glances/
$ ls /etc/glances/

If you are downloading a heavy file, you may want to add the -c or --continue flag, which means continue getting a partially-downloaded file. With it, you don’t have to start the download afresh.

This option helps you to resume downloading a file started by a previous instance of wget, or by another program or one that you had paused. It is also useful in case of any network failure. For example,

$ wget -c https://tenet.dl.sourceforge.net/project/parrotsecurity/iso/4.1/Parrot-security-4.1_amd64.iso

For more information, see the wget man page.

$ man wget 

You might also like to read these following related articles.

1. How to Download and Extract Tar Files with One Command
2. 5 Linux Command Line Based Tools for Downloading Files and Browsing Websites
3. 15 Tips On How to Use ‘Curl’ Command in Linux

That’s all! In this short article, we have explained how to download files to a specific directory without moving into that directory, using wget. You can share your thoughts with us in the comments.

Source

In this article we’ll see how we can use Dmidecode command to retrieve hardware information of any Linux system. Suppose if we want to upgrade a system we need to gather information like Memory, BIOS and CPUetc. With help of Dmidecode command we will come to know the details without opening system chasis. Dmidecode command works for RHEL/CentOS/Fedora/Ubuntu Linux.

Dmidecode tool read DMI (some say SMBIOS) table to fetch data and displays useful system informations like hardware details, serial numbers and BIOS version, Processor etc. in human readable format. You may require root priviledge to execute dmidecode command.

1. Basic Output of Demidecode

Below is the Demidecode command sample output.

# dmidecode 2.11
SMBIOS version fixup (2.31 -> 2.3).
SMBIOS 2.3 present.
45 structures occupying 1642 bytes.
Table at 0x000E0010.

Handle 0x0000, DMI type 0, 20 bytes
BIOS Information
        Vendor: Phoenix Technologies LTD
        Version: 6.00
        Release Date: 12/06/2006
        Address: 0xE78A0
        Runtime Size: 100192 bytes
        ROM Size: 64 kB
        Characteristics:
                ISA is supported
                PCI is supported
                PC Card (PCMCIA) is supported
                PNP is supported
                APM is supported
                BIOS is upgradeable
                BIOS shadowing is allowed
                ESCD support is available
               USB legacy is supported
                Smart battery is supported
                BIOS boot specification is supported

2. How to Get DMI Types

DMI Id give us particular hardware information of system. Dmidecode with options ‘-t ‘or ‘–type‘ and ‘Id‘ will provide us the exact infromation. Id 6 will give us Memory Module information.

[root@tecmint ~]# dmidecode -t 6
# dmidecode 2.11
SMBIOS version fixup (2.31 -> 2.3).
SMBIOS 2.3 present.

Handle 0x0009, DMI type 6, 12 bytes
Memory Module Information
        Socket Designation: RAM socket #0
        Bank Connections: 0 1
        Current Speed: Unknown
        Type: EDO DIMM
        Installed Size: 1024 MB (Single-bank Connection)
        Enabled Size: 1024 MB (Single-bank Connection)
        Error Status: OK

Handle 0x000A, DMI type 6, 12 bytes
Memory Module Information
        Socket Designation: RAM socket #1
        Bank Connections: 2 3
        Current Speed: Unknown
        Type: EDO DIMM
        Installed Size: Not Installed
        Enabled Size: Not Installed
        Error Status: OK

Handle 0x000B, DMI type 6, 12 bytes
Memory Module Information
        Socket Designation: RAM socket #2
        Bank Connections: 4 5
        Current Speed: Unknown
        Type: EDO DIMM
        Installed Size: Not Installed
        Enabled Size: Not Installed
        Error Status: OK

Handle 0x000C, DMI type 6, 12 bytes
Memory Module Information
        Socket Designation: RAM socket #3
        Bank Connections: 6 7
        Current Speed: Unknown
        Type: EDO DIMM
        Installed Size: Not Installed
        Enabled Size: Not Installed
        Error Status: OK

		Type   Information
		----------------------------------------
          0		BIOS
          1		System
          2		Base Board
          3		Chassis
          4		Processor
          5		Memory Controller
          6		Memory Module
          7		Cache
          8		Port Connector
          9		System Slots
         10		On Board Devices
         11		OEM Strings
         12		System Configuration Options
         13		BIOS Language
         14		Group Associations
         15		System Event Log
         16		Physical Memory Array
         17		Memory Device
         18		32-bit Memory Error
         19		Memory Array Mapped Address
         20		Memory Device Mapped Address
         21		Built-in Pointing Device
         22		Portable Battery
         23		System Reset
         24		Hardware Security
         25		System Power Controls
         26		Voltage Probe
         27		Cooling Device
         28		Temperature Probe
         29		Electrical Current Probe
         30		Out-of-band Remote Access
         31		Boot Integrity Services
         32		System Boot
         33		64-bit Memory Error
         34		Management Device
         35		Management Device Component
         36		Management Device Threshold Data
         37		Memory Channel
         38		IPMI Device
         39		Power Supply

Instead of going with ‘type_id‘ you can also use keyword with ‘-t‘ argument to the dmidecode command. Following are the list of available keywords.

	Keyword     Types
       ------------------------------
       bios        0, 13
       system      1, 12, 15, 23, 32
       baseboard   2, 10
       chassis     3
       processor   4
       memory      5, 6, 16, 17
       cache       7
       connector   8
       slot        9

For example, to get the Cache information on system, you can execute below command instead of Id 7.

[root@tecmint ~]# dmidecode -t cache
# dmidecode 2.11
SMBIOS version fixup (2.31 -> 2.3).
SMBIOS 2.3 present.

Handle 0x000D, DMI type 7, 19 bytes
Cache Information
        Socket Designation: L1 Cache
        Configuration: Enabled, Socketed, Level 1
        Operational Mode: Write Back
        Location: Internal
        Installed Size: 16 kB
        Maximum Size: 16 kB
        Supported SRAM Types:
                Burst
                Pipeline Burst
                Asynchronous
        Installed SRAM Type: Asynchronous
        Speed: Unknown
        Error Correction Type: Unknown
        System Type: Unknown
        Associativity: Unknown

Handle 0x000E, DMI type 7, 19 bytes
Cache Information
        Socket Designation: L2 Cache
        Configuration: Enabled, Socketed, Level 2
        Operational Mode: Write Back
        Location: External
        Installed Size: 0 kB
        Maximum Size: 512 kB
        Supported SRAM Types:
                Burst
                Pipeline Burst
                Asynchronous
        Installed SRAM Type: None
        Speed: Unknown
        Error Correction Type: Unknown
        System Type: Unknown
        Associativity: Unknown

3. How to Get Memory Information

How do i get Memory information on system and how much memory is supported by system? The following command shows that the system can support maximum 4GB of RAM.

[root@tecmint ~]# dmidecode -t 16
# dmidecode 2.11
SMBIOS version fixup (2.31 -> 2.3).
SMBIOS 2.3 present.

Handle 0x001D, DMI type 16, 15 bytes
Physical Memory Array
        Location: System Board Or Motherboard
        Use: System Memory
        Error Correction Type: None
        Maximum Capacity: 4 GB
        Error Information Handle: Not Provided
        Number Of Devices: 4

Note: From the keyword list the memory related information IDs are 5, 6, 16 and 17.

4. How Do I Get BIOS information?

To get the BIOS information of the system, run the following command with ‘-t’ option.

[root@tecmint ~]# dmidecode -t bios
# dmidecode 2.11
SMBIOS version fixup (2.31 -> 2.3).
SMBIOS 2.3 present.

Handle 0x0000, DMI type 0, 20 bytes
BIOS Information
        Vendor: Phoenix Technologies LTD
        Version: 6.00
        Release Date: 12/06/2006
        Address: 0xE78A0
        Runtime Size: 100192 bytes
        ROM Size: 64 kB
        Characteristics:
                ISA is supported
                PCI is supported
                PC Card (PCMCIA) is supported
                PNP is supported
                APM is supported
                BIOS is upgradeable
                BIOS shadowing is allowed
                ESCD support is available
                USB legacy is supported
                Smart battery is supported
                BIOS boot specification is supported

5. How Do I Get the Manufacturer, Model and Serial Number?

To get the information about Manufacturer, Model and Serial Number of system, use the following command as shown below.

[root@tecmint ~]# dmidecode -t system
# dmidecode 2.11
SMBIOS 2.4 present.

Handle 0x0001, DMI type 1, 27 bytes
System Information
        Manufacturer: LENOVO
        Product Name: 9637C76
        Version: ThinkCentre M55e
        Serial Number: L9BT188
        UUID: 8015D37A-2F82-DC11-A3FB-8C6E4EBAD5CE
        Wake-up Type: AC Power Restored
        SKU Number: Not Specified
        Family: Not Specified

Handle 0x000F, DMI type 12, 5 bytes
System Configuration Options
        Option 1: Jumper settings can be described here.

Handle 0x0010, DMI type 15, 29 bytes
System Event Log
        Area Length: 432 bytes
        Header Start Offset: 0x0000
        Header Length: 16 bytes
        Data Start Offset: 0x0010
        Access Method: General-purpose non-volatile data functions
        Access Address: 0x0000
        Status: Valid, Not Full
        Change Token: 0x0000001A
        Header Format: Type 1
        Supported Log Type Descriptors: 3
        Descriptor 1: POST error
        Data Format 1: POST results bitmap
        Descriptor 2: Single-bit ECC memory error
        Data Format 2: Multiple-event
        Descriptor 3: Multi-bit ECC memory error
        Data Format 3: Multiple-event

Handle 0x0017, DMI type 23, 13 bytes
System Reset
        Status: Enabled
        Watchdog Timer: Present
        Boot Option: Do Not Reboot
        Boot Option On Limit: Do Not Reboot
        Reset Count: Unknown
        Reset Limit: Unknown
        Timer Interval: Unknown
        Timeout: Unknown

Handle 0x001F, DMI type 32, 20 bytes
System Boot Information
        Status:

Please run ‘man dmidecode‘ from terminal or command prompt to know more about dmidecode.

Read Also: 10 Command Line Tools to Get Linux Hardware Information

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In this post, we are going to review how we can assign Static IP Address, Static Route, Default Gateway etc.  Assigning IP Address on demand using IP command. IFCONFIG command is deprecated and replaced by IPcommand in Linux. However, IFCONFIG command is still works and available for most of the Linux distributions.

Don’t Miss: ifconfig vs ip: What’s Difference and Comparing Commands

Note: Please take configuration file backup before doing any changes.

How do i Configure Static IP Address Internet Protocol (IPv4)

To configure static IP Address, you need to update or edit network configuration file to assign an Static IP Address to a system. You must be superuser with su (switch user) command from terminal or command prompt.

For RHEL/CentOS/Fedora

Open and edit network configuration file for (eth0 or eth1) using your favorite editor. For example, to assigning IP Address to eth0 interface as follows.

[root@tecmint ~]# vi /etc/sysconfig/network-scripts/ifcfg-eth0

Simple output:

DEVICE="eth0"
BOOTPROTO=static
ONBOOT=yes
TYPE="Ethernet"
IPADDR=192.168.50.2
NAME="System eth0"
HWADDR=00:0C:29:28:FD:4C
GATEWAY=192.168.50.1

For Ubuntu/Debian/Linux Mint

Assign Static IP Address to eth0 interface editing configuration file /etc/network/interfaces to make permanent changes as shown below.

auto eth0
iface eth0 inet static
address 192.168.50.2
netmask 255.255.255.0
gateway 192.168.50.1

Next, restart network services after entering all the details using the following command.

# /etc/init.d/networking restart

$ sudo /etc/init.d/networking restart

1. How to Assign a IP Address to Specific Interface

The following command used to assign IP Address to a specific interface (eth1) on the fly.

# ip addr add 192.168.50.5 dev eth1

$ sudo ip addr add 192.168.50.5 dev eth1

Note: Unfortunately all these settings will be lost after a system restart.

2. How to Check an IP Address

To get the depth information of your network interfaces like IP Address, MAC Address information, use the following command as shown below.

# ip addr show

$ sudo ip addr show

Sample Output

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 00:0c:29:28:fd:4c brd ff:ff:ff:ff:ff:ff
    inet 192.168.50.2/24 brd 192.168.50.255 scope global eth0
    inet6 fe80::20c:29ff:fe28:fd4c/64 scope link
       valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 00:0c:29:28:fd:56 brd ff:ff:ff:ff:ff:ff
    inet 192.168.50.5/24 scope global eth1
    inet6 fe80::20c:29ff:fe28:fd56/64 scope link
       valid_lft forever preferred_lft forever

3. How to Remove an IP Address

The following command will remove an assigned IP address from the given interface (eth1).

# ip addr del 192.168.50.5/24 dev eth1

$ sudo ip addr del 192.168.50.5/24 dev eth1

4. How to Enable Network Interface

The “up” flag with interface name (eth1) enables a network interface. For example, the following command will activates the eth1 network interface.

# ip link set eth1 up

$ sudo ip link set eth1 up

5. How to Disable Network Interface

The “down” flag with interface name (eth1) disables a network interface. For example, the following command will De-activates the eth1 network interface.

# ip link set eth1 down

$ sudo ip link set eth1 down

6. How do I Check Route Table?

Type the following command to check the routing table information of system.

# ip route show

$ sudo ip route show

Sample Output

10.10.20.0/24 via 192.168.50.100 dev eth0
192.168.160.0/24 dev eth1  proto kernel  scope link  src 192.168.160.130  metric 1
192.168.50.0/24 dev eth0  proto kernel  scope link  src 192.168.50.2
169.254.0.0/16 dev eth0  scope link  metric 1002
default via 192.168.50.1 dev eth0  proto static

7. How do I Add Static Route

Why you need to add Static routes or Manual routes, because that the traffic must not pass through the default gateway. We need to add Static routes to pass traffic from best way to reach the destination.

# ip route add 10.10.20.0/24 via 192.168.50.100 dev eth0

$ sudo ip route add 10.10.20.0/24 via 192.168.50.100 dev eth0

8. How to Remove Static Route

To remove assigned static route, simply type the following command.

# ip route del 10.10.20.0/24

$ sudo ip route del 10.10.20.0/24

9. How do I Add Persistence Static Routes

All the above route will be lost after a system restart. To add permanent Static route, edit file /etc/sysconfig/network-scripts/route-eth0 (We are storing static route for (eth0) and add the following lines and save and exist. By default route-eth0 file will not be there, need to be created.

For RHEL/CentOS/Fedora

# vi /etc/sysconfig/network-scripts/route-eth0
10.10.20.0/24 via 192.168.50.100 dev eth0

For Ubuntu/Debian/Linux Mint

Open the file /etc/network/interfaces and at the end add the persistence Static routes. IP Addresses may differ in your environment.

$ sudo vi /etc/network/interfaces

auto eth0
iface eth0 inet static
address 192.168.50.2
netmask 255.255.255.0
gateway 192.168.50.100
#########{Static Route}###########
up ip route add 10.10.20.0/24 via 192.168.50.100 dev eth0

Next, restart network services after entering all the details using the following command.

# /etc/init.d/network restart

$ sudo /etc/init.d/network restart

10. How do I Add Default Gateway

Default gateway can be specified globally or for in interface-specific config file. Advantage of default gateway is If we have more than one NIC is present in the system. You can add default gateway on the fly as shown below command.

# ip route add default via 192.168.50.100

$ sudo ip route add default via 192.168.50.100

Kindly correct me if i missed out. Please refer manual page doing man ip from terminal/command prompt to know more about IP Command.

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