Linux show active connections


  • 6 commands to check and list active SSH connections in Linux
  • Finding Open Files and Network Connections
  • How to Find All Clients Connected to HTTP or HTTPS Ports
  • 12 ss Command Examples to Monitor Network Connections
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  • Postgres Check Connections are Active
  • 6 commands to check and list active SSH connections in Linux

    Share Tweet Email If you suspect a network issue on your Linux system, here's how to trace and troubleshoot it with the ss command. Linux utilities are a lifesaver for server administrators when it comes to troubleshooting and fixing network issues. Before, administrators used the netstat command to view network statistics and other socket-related information on Linux. But this command has now been deprecated for a better tool. The ss command replaced netstat as it provides more detailed information than its predecessor.

    This article will demonstrate how you can use ss to extract socket-related information from your system. What Is the ss Command? The ss command, short for socket statistics, is a Linux utility that displays information related to network connections in a detailed and human-readable format.

    You can use ss to troubleshoot and find issues with your network as it provides complete details on the connections. As mentioned before, ss replaced netstat, which was the original utility for listing socket statistics on Linux.

    The ss command is easy to use, provides more information, and delivers quick and accurate results. How to Use ss on Linux Using ss, you can list all the socket connections on your system. Furthermore, filtering the connections based on the type, destination address, and port number is also possible. Basic Syntax The basic syntax of the ss command is: ss options The most simple ss command displays a list of all the established connections, irrespective of the connection type.

    ESTAB, which denotes an established connection. You will find the following column headings in the output: Netid: This denotes the type of socket used for the connection. State: The State column displays the status of the connection.

    Recv-Q: The number of received packets present in the queue. Send-Q: The number of sent packets in the queue. Local address and port: The local address of the user's machine and the port number. Peer address and port: The address of the destination machine and the port number. Get a List of All Sockets Use the -a flag to display all the sockets present in the network, listening or non-listening.

    The -l stands for Listening. Note that almost every socket in the output has an unconnected state. As soon as a listening socket gets an incoming connection, it creates a child socket and uses it to establish the connection. You can then use the Linux tcpdump utility to monitor and filter packets on your network. You can list all the connections belonging to a specific socket type with ss. To list every TCP socket on your computer: ss -t The -u flag will display a list of all the UDP sockets: ss -u To retrieve a list of Unix sockets using ss, use the -x flag: ss -x Output: By default, ss only displays the connected sockets.

    To get a list of all the sockets, irrespective of the connection state, use the -a flag with the command: ss -ta ss -xa Filter TCP Connections Using State TCP sockets have multiple states that you can use to filter the results.

    You can use the following socket states to filter the connections with ss: established, closed, listening, closing, all, connected, synchronized, bucket, big, time-wait, etc.

    Finding Open Files and Network Connections

    It gives an overview of network activities and displays which ports are open or have established connections. The netstat tool is essential for discovering network problems. This article shows 28 netstat commands for displaying port and internet statistics data on Linux. Prerequisites Access to the terminal Installed net-tools software package Note: Though still widely used, netstat command is considered obsolete. Instead, the ss command is recommended as a faster and simpler tool.

    Learn more about the Linux ss command. How to Use netstat Command in Linux The primary usage of netstat is without any parameters: netstat The first list in the output displays active established internet connections on the computer. Recv-Q — Receive queue of bytes received or ready to be received.

    Send-Q — Send queue of bytes ready to be sent. Local address — Address details and port of the local connection. Foreign address— Address details and port of the remote end of the connection. The second list shows all the active "Unix Domain" open sockets with the following details: Proto — Protocol used by the socket always unix.

    RefCnt — Reference count of the number of attached processes to this socket. Flags — Usually ACC or blank. Type — The socket type. I-Node — File system inode index node associated with this socket. Path — System path to the socket. For advanced usage, expand the netstat command with options: netstat [options] Or list the options one by one: netstat [option 1] [option 2] [option 3] The netstat options enable filtering of network information.

    Note: If the network is slow, test the network speed. List All Ports and Connections To list all ports and connections regardless of their state or protocol, use: netstat -a The output lists established connections along with servers which are open or listening.

    How to Find All Clients Connected to HTTP or HTTPS Ports

    In this tutorial, we will show how to find active SSH connections using various methods in Linux. Prerequisites A server runs Linux operating system. You have root access on that server. Find active SSH connection with the who command which is the Linux command line utility used to display a list of users currently logged into server. Find active SSH connection with the w command w is another command line utility that displays information about currently logging in users on your server.

    This command provides more information than who commands as active sessions and run process on those sessions.

    12 ss Command Examples to Monitor Network Connections

    You can run the w command shown below: w You should get the following output: up 1 day,2 users, load average: 0. Find active SSH connection with ps command ps command also gives you information about active SSH sessions on your server.

    For example the Apache httpd server opens port So if you want to check whether any http server is running or not, or which http server is running, apache or nginx, then track down the process name. The process details are made available by the 'p' option. Use the e option along with the p option to get the username too.

    The extended information contains the username and inode of the process. This is a useful command for network administrators. Note - If you use the n option with the e option, the uid would be listed and not the username.

    Print statistics The netstat command can also print out network statistics like total number of packets received and transmitted by protocol type and so on. To print out statistics of only select protocols like TCP or UDP use the corresponding options like t and u along with the s option.

    Display kernel routing information The kernel routing information can be printed with the r option.

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    It is the same output as given by the route command. We also use the n option to disable the hostname lookup. Print network interfaces The netstat command can also print out the information about the network interfaces. The "-i" option does the task. To get a more human friendly version of the output use the e option along with i.

    Get netstat output continuously Netstat can output connection information continuously with the c option. Display multicast group information The g option will display the multicast group information for IPv4 and IPv6 protocols.

    Postgres Check Connections are Active

    Now its time to do some geek stuff with style. Grep for http or smtp or whatever you are looking for. Conclusion Well, that was most of what netstat is used for. If you are looking for more advanced information or want to dig deeper, read up the netstat manual man netstat.


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