Get ip on linux machine

How can I get the IP address of a (Linux) machine?

I need to find the external IP address to bind my application to it. Obviously I can also bind to INADDR_ANY (and actually that’s what I do at the moment). I would prefer to detect the public address, though.

Why mark down the popen of ifconfig? It’s really the right thing to do. Libraries change, but ifconfig and popen will always be there.

ifconfig still, today, works on more architectures than any other approach. So change it to the ip command.when/if appropriate. popen is still the better solution.

12 Answers 12

I found the ioctl solution problematic on os x (which is POSIX compliant so should be similiar to linux). However getifaddress() will let you do the same thing easily, it works fine for me on os x 10.5 and should be the same below.

I’ve done a quick example below which will print all of the machine’s IPv4 address, (you should also check the getifaddrs was successful ie returns 0).

I’ve updated it show IPv6 addresses too.

#include #include #include #include #include #include int main (int argc, const char * argv[]) < struct ifaddrs * ifAddrStruct=NULL; struct ifaddrs * ifa=NULL; void * tmpAddrPtr=NULL; getifaddrs(&ifAddrStruct); for (ifa = ifAddrStruct; ifa != NULL; ifa = ifa->ifa_next) < if (!ifa->ifa_addr) < continue; >if (ifa->ifa_addr->sa_family == AF_INET) < // check it is IP4 // is a valid IP4 Address tmpAddrPtr=&((struct sockaddr_in *)ifa->ifa_addr)->sin_addr; char addressBuffer[INET_ADDRSTRLEN]; inet_ntop(AF_INET, tmpAddrPtr, addressBuffer, INET_ADDRSTRLEN); printf("%s IP Address %s\n", ifa->ifa_name, addressBuffer); > else if (ifa->ifa_addr->sa_family == AF_INET6) < // check it is IP6 // is a valid IP6 Address tmpAddrPtr=&((struct sockaddr_in6 *)ifa->ifa_addr)->sin6_addr; char addressBuffer[INET6_ADDRSTRLEN]; inet_ntop(AF_INET6, tmpAddrPtr, addressBuffer, INET6_ADDRSTRLEN); printf("%s IP Address %s\n", ifa->ifa_name, addressBuffer); > > if (ifAddrStruct!=NULL) freeifaddrs(ifAddrStruct); return 0; > 

+1 and thanks for bringing this nice approach instead of those boring ioctl’s! However, your handling of IP6 is still incorrect — you should cast to sockaddr_in6, i.e. something like tmpAddrPtr=&((struct sockaddr_in6 *)ifa->ifa_addr)->sin6_addr;

gives lo and wlan0 interfaces in my case. What I require is wlan0 or eth0 which has internet connection.So, Should I use strcmp or thre’s a better way?

Read /usr/include/linux/if.h for information on the ifconf and ifreq structures. This should give you the IP address of each interface on the system. Also read /usr/include/linux/sockios.h for additional ioctls.

@MattJoiner No, take a look at the man page, SIOCGIFCONF returns info on all interfaces. Part of the man page quoted here: «Return a list of interface (transport layer) addresses. This currently means only addresses of the AF_INET (IPv4) family for compatibility. The user passes a ifconf structure as argument to the ioctl. It contains a pointer to an array of ifreq structures in ifc_req and its length in bytes in ifc_len. The kernel fills the ifreqs with all current L3 interface addresses that are running»

I like jjvainio’s answer. As Zan Lnyx says, it uses the local routing table to find the IP address of the ethernet interface that would be used for a connection to a specific external host. By using a connected UDP socket, you can get the information without actually sending any packets. The approach requires that you choose a specific external host. Most of the time, any well-known public IP should do the trick. I like Google’s public DNS server address 8.8.8.8 for this purpose, but there may be times you’d want to choose a different external host IP. Here is some code that illustrates the full approach.

void GetPrimaryIp(char* buffer, size_t buflen) < assert(buflen >= 16); int sock = socket(AF_INET, SOCK_DGRAM, 0); assert(sock != -1); const char* kGoogleDnsIp = "8.8.8.8"; uint16_t kDnsPort = 53; struct sockaddr_in serv; memset(&serv, 0, sizeof(serv)); serv.sin_family = AF_INET; serv.sin_addr.s_addr = inet_addr(kGoogleDnsIp); serv.sin_port = htons(kDnsPort); int err = connect(sock, (const sockaddr*) &serv, sizeof(serv)); assert(err != -1); sockaddr_in name; socklen_t namelen = sizeof(name); err = getsockname(sock, (sockaddr*) &name, &namelen); assert(err != -1); const char* p = inet_ntop(AF_INET, &name.sin_addr, buffer, buflen); assert(p); close(sock); > 

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Get an IP Address on Linux : Discover the Many Ways

Your IP address is like your home address, and it’s how the internet knows where to send the data you’ve requested. Knowing your IP address is handy in many ways, like remotely managing your server. But how do you get an IP address on Linux?

In this tutorial, you’ll learn many ways to find your IP address on Linux, whether using the command line or checking through system settings.

Read on and pick off how you’d like to get your IP address!

Prerequisites

This tutorial will be a hands-on demonstration. If you’d like to follow along, be sure you have the following:

• A Linux machine – You can use a virtual machine, a dedicated server, or even your local Windows 10 computer with Windows Subsystem for Linux (WSL) – This tutorial uses Ubuntu 20.04 LTS, but other Linux distros will work.

• NET-3 networking toolkit installed.

• This tutorial assumes you’ve already logged/SSH into the system as a user with sudo privileges – This tutorial uses the root user to execute all the commands.

If you’re not logged in as a root user, prepend sudo to this tutorial’s commands.

Get an IP Address on Linux with the curl Command

A popular tool called cURL lets you transfer data specified with URL syntax. This tool supports protocols like DICT, FILE, FTP, FTPS, Gopher, HTTP, HTTPS, IMAP, etc.

But the important question is, can you get your public IP address with the curl command? Yes! Getting your public IP address is just one of the cURL’s powerful features.

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Run the below command to perform the following in finding your public IP address:

• curl – Uses the Google Search API to fetch the first result of the query “ what is my ip address .”
• The -s option tells curl to perform a silent request. The output is then piped to grep , which extracts only the IP address from the response using a regular expression.
• The -oE portion of the grep command stands for “only match,” which outputs only the matching IP address and not the whole response.
• The -m1 option tells grep to stop after the first match. Why? Google Search API returns a bunch of HTML code along with the IP address; you don’t need that.

curl -s | grep -oE "\\b(2.)5\\b" -m1 

Below, you can see your public IP address printed out.

Get an IP Address on Linux with the wget Command

Like cURL, Wget is a free utility that lets you retrieve files using the most widely-used Internet protocols (HTTP, HTTPS, and FTP).

Wget lets you download single files, whole websites, or even mirror an entire website, and of course, find your IP address.

Run the below wget command to find, and display your public IP address to the terminal with the following:

• The wget command sends an HTTP request to https://ipecho.net/plain and retrieves the content of that page.
• The -qO option tells wget to be quiet and print as little output as possible to the terminal.
• The output of the wget command is piped to the xargs echo command to display the output in a single line.

Now, you can share the IP address with your users so that they can connect to the server via SSH.

Digging Your Public IP Address with the dig Command

The Domain Information Groper ( dig ) command is used for querying DNS servers, but you can also use this command to find your public IP address.

Suppose you sent a ping request to your web server’s public IP address. If you received the ping response, you know that your web server is running and accessible from the outside world. If not, you may have to troubleshoot the issue to identify the problem, and your first step is to find your public IP address.

Run the below dig command to query your web server’s public IP address.

• The below command uses OpenDNS nameservers ( resolver1.opendns.com ) to find your public IP address. OpenDNS servers are a good idea as they are reliable and offer better security features, such as phishing protection and content filtering.
• The +short option instructs dig to print the output in a short format, while myip.opendns.com is the hostname that returns your public IP address.

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

Now, run the ping command below to send a ping request every 10 seconds. Replace IP_address with your web server’s actual public IP address.

Finding Your Private IP Address Using the ifconfig Command

At this point, you already know how to find your public IP address. But in some cases, you may need to know the private IP address of your Linux server to connect to it from another device on the same network.

How to get your private IP address? The ifconfig command will do the trick.

Run the ifconfig command below to display all ( -a ) network adapters on your system and their configuration, including your private IP address.

As you can see below, one system can have more than one network adapter. Each adapter can have a different IP address.

Look for the inet entry under the ethh0 or wlan0 adapter to find your private IPv4 address, as shown below.

Writing a Bash Script to Find Your IP Address

Perhaps you need a way to find your IP address automatically. If so, writing a Bash script is an excellent choice to find your public and private IP addresses.

Why use a script? You can use the same script on multiple systems, saving yourself the hassle of running the commands on each system.

1. Open a new find_ip.sh file in your preferred text editor.

2. Add the following code to the find_ip.sh file, save the file and close the editor.

The code below finds and stores your private and public IP addresses on the lanIp and wanIp variables and prints them on the terminal.

#!/bin/bash # Find your private IP address and store the value to the lanIp variable lanIp="$(ip -4 -o -br addr|awk '$0 ~ /^[we]\w+\s+UP\s+/ ')"; # Find your public IP address and store the value to the wanIp variable wanIp="$(curl https://ipinfo.io/ip 2>/dev/null)"; # Print the values of the lanIp and wanIp variables echo "Your private ip is: $"; echo "Your public ip is: $";

Storing your server’s public IP address in an environment variable is handy for a CD/CI tool, such as Jenkins or TravisCI.

3. Finally, run the below sh command to execute the find_ip.sh script to find your IP addresses.

You will see an output similar to the following, showing your public and private IP addresses.

Conclusion

In this tutorial, you’ve learned how to find/get your IP address on Linux using a few different commands, like the curl and ifconfig . You also wrote a script to automate finding IP addresses on multiple systems.

Now that you know how to find your IP address on Linux, you can use this information for different tasks. Perhaps to configure a Cloudflare dynamic DNS for your home network?

Hate ads? Want to support the writer? Get many of our tutorials packaged as an ATA Guidebook.

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How to get the IP address of a Unix machine?

I need to know the IP address of a UNIX machine. I can login to it with ssh but don’t know the IP address. Can anyone please tell me a command to get the IP address of the Unix machine I logged in to?

5 Answers 5

try this code to see the IP address of unix machine

You can use ifconfig to get the IP address of any of the interfaces on the system (note that there may well be more than one interface and more than one IP address).

Some UNIX systems do not label their interfaces en0 — a more general answer is to use ifconfig -a . Also, the ifconfig binary is not always on the PATH for ordinary users so they may need to try various incantations such as /sbin/ifconfig -a , /etc/ifconfig -a or login as root and try ifconfig -a .

Use this command

nslookup `hostname` | grep -i address | awk -F" " '' | awk -F# '' | tail -n 1 

Explanation

nslookup `hostname` | grep -i address 

This will return something like

Address: 192.168.1.1#53 Address: 192.168.1.167 

Now let’s retrieve only the addresses by selecting the second column of text. We pass » » as the field separator

nslookup `hostname` | grep -i address | awk -F" " '' 

We’ll get rid of the «#53» part by selecting the first column. We pass «#» as the field separator

nslookup `hostname` | grep -i address | awk -F" " '' | awk -F# '' 

The last address is the local address. Tail will help us get it.

nslookup `hostname` | grep -i address | awk -F" " '' | awk -F# '' | tail -n 1 

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