How do i list all available system sockets on a linux os?

  • Note: This is for newer versions of linux. Linux meaning popular Linux Operating Systems.

    What is the difference between --list-unit-files and --list-units?

           list-unit-files [PATTERN...]
               List unit files installed on the system, in combination with their enablement state
               (as reported by is-enabled). If one or more PATTERNs are specified, only unit files
               whose name matches one of them are shown (patterns matching unit file system paths
               are not supported).
           list-units [PATTERN...]
               List units that systemd currently has in memory. This includes units that are
               either referenced directly or through a dependency, units that are pinned by
               applications programmatically, or units that were active in the past and have
               failed. By default only units which are active, have pending jobs, or have failed
               are shown; this can be changed with option --all. If one or more PATTERNs are
               specified, only units matching one of them are shown. The units that are shown are
               additionally filtered by --type= and --state= if those options are specified.
    $ systemctl list-unit-files --type=socket
    UNIT FILE                       STATE   
    acpid.socket                    enabled 
    apport-forward.socket           enabled 
    avahi-daemon.socket             enabled 
    cups.socket                     enabled 
    dbus.socket                     static  
    docker.socket                   enabled 
    saned.socket                    disabled
    snapd.socket                    enabled 
    ssh.socket                      disabled
    syslog.socket                   static  
    systemd-fsckd.socket            static  
    systemd-initctl.socket          static  
    systemd-journald-audit.socket   static  
    systemd-journald-dev-log.socket static  
    systemd-journald.socket         static  
    systemd-networkd.socket         disabled
    systemd-rfkill.socket           static  
    systemd-udevd-control.socket    static  
    systemd-udevd-kernel.socket     static  
    uuidd.socket                    enabled 
    20 unit files listed.
    $ systemctl list-units --type=socket
    UNIT                            LOAD   ACTIVE SUB       DESCRIPTION                             
    acpid.socket                    loaded active running   ACPID Listen Socket                     
    avahi-daemon.socket             loaded active running   Avahi mDNS/DNS-SD Stack Activation Socket
    cups.socket                     loaded active running   CUPS Scheduler                          
    dbus.socket                     loaded active running   D-Bus System Message Bus Socket         
    docker.socket                   loaded active running   Docker Socket for the API               
    snapd.socket                    loaded active running   Socket activation for snappy daemon     
    syslog.socket                   loaded active running   Syslog Socket                           
    systemd-fsckd.socket            loaded active listening fsck to fsckd communication Socket      
    systemd-initctl.socket          loaded active listening /dev/initctl Compatibility Named Pipe   
    systemd-journald-audit.socket   loaded active running   Journal Audit Socket                    
    systemd-journald-dev-log.socket loaded active running   Journal Socket (/dev/log)               
    systemd-journald.socket         loaded active running   Journal Socket                          
    systemd-rfkill.socket           loaded active listening Load/Save RF Kill Switch Status /dev/rfki
    systemd-udevd-control.socket    loaded active running   udev Control Socket                     
    systemd-udevd-kernel.socket     loaded active running   udev Kernel Socket                      
    uuidd.socket                    loaded active listening UUID daemon activation socket           
    LOAD   = Reflects whether the unit definition was properly loaded.
    ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
    SUB    = The low-level unit activation state, values depend on unit type.
    16 loaded units listed. Pass --all to see loaded but inactive units, too.

    As we are on the topic of sockets. The --list-sockets option:

          list-sockets [PATTERN...]
               List socket units currently in memory, ordered by listening address. If one or more
               PATTERNs are specified, only socket units matching one of them are shown.

    Here you can see the listening address and what service uses it.

    $ systemctl list-sockets -all
    LISTEN                          UNIT                            ACTIVATES
    /dev/rfkill                     systemd-rfkill.socket           systemd-rfkill.service
    /run/acpid.socket               acpid.socket                    acpid.service
    /run/apport.socket              apport-forward.socket          
    /run/avahi-daemon/socket        avahi-daemon.socket             avahi-daemon.service
    /run/cups/cups.sock             cups.socket                     cups.service
    /run/snapd-snap.socket          snapd.socket                    snapd.service
    /run/snapd.socket               snapd.socket                    snapd.service
    /run/systemd/fsck.progress      systemd-fsckd.socket            systemd-fsckd.service
    /run/systemd/initctl/fifo       systemd-initctl.socket          systemd-initctl.service
    /run/systemd/journal/dev-log    systemd-journald-dev-log.socket systemd-journald.service
    /run/systemd/journal/socket     systemd-journald.socket         systemd-journald.service
    /run/systemd/journal/stdout     systemd-journald.socket         systemd-journald.service
    /run/systemd/journal/syslog     syslog.socket                   rsyslog.service
    /run/udev/control               systemd-udevd-control.socket    systemd-udevd.service
    /run/uuidd/request              uuidd.socket                    uuidd.service
    /var/run/dbus/system_bus_socket dbus.socket                     dbus.service
    /var/run/docker.sock            docker.socket                   docker.service
    audit 1                         systemd-journald-audit.socket   systemd-journald.service
    kobject-uevent 1                systemd-udevd-kernel.socket     systemd-udevd.service
    19 sockets listed.

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