Unix domain (UD) sockets are an inter-process communication (IPC) mechanism that allows bidirectional data exchange between processes running on the same platform. They are sometimes called local sockets. Communication occurs entirely within the operating system kernel. The closest IPC mechanism to a UD socket is probably a Unix pipe or a Linux Netlink socket. Note that the term domain in UD has nothing to do with DNS, NIS, LDAP, or Active Directory, and instead refers to the file system.
A UD socket is uniquely identified by a filesystem pathname. Obviously, both processes have to agree on the pathname for them to communicate with each other. Technically, UD sockets use the filesystem as their address name space and they are referenced by processes as inodes in the filesystem. Processes using UD sockets do not need to share a common ancestry.
UD sockets are a completely separate mechanism from network sockets which can use IP sockets to communicate between processes running on the same platform via an IPv4 or IPv6 loopback interface. UD sockets can avoid some checks and operations that IP sockets have to perform. This makes them faster and lighter-weight compared with IP sockets. Thus a UD socket does not require any network support to work. UD sockets are not limited to just two processes, many processes can use the same UD socket. For this reason, a popular use case for UD sockets is client-server applications.
A UD socket may be created as connection‑mode (SOCK_STREAM or SOCK_SEQPACKET) sockets or as connectionless (SOCK_DGRAM) sockets, while pipes are standard streams only. Communication is bidirectional with stream sockets and unidirectional with datagram sockets.
File and directory permissions can be used to restrict which processes on a platform can open or access a UD socket, and thus communicate with another process. Thus UD socket security is superior to IP sockets to which anyone can connect, unless extra authentication logic is in place. Remote hosts cannot connect to a UD socket without some sort of a forwarding mechanism. Neither can UD sockets be eavesdropped on by an IP socket without some sort of forwarding mechanism.
Linux supports a type of UD socket called an abstract named socket which is identical to regular UD socket except that a proper pathname does not exist in the filesystem. File permissions do not apply to abstract named sockets, and they can be accessed from inside chroot jails. The trick used is to make the first byte of the bind address name a null.
A UD socket is represented in the following structure:
#define UNIX_PATH_MAX 108
struct sockaddr_un {
sa_family_t sun_family; /* AF_UNIX */
char sun_path[UNIX_PATH_MAX]; /* pathname */
};
Three types of address are distinguished in this structure:
- pathname: a UNIX domain socket can be bound to a null-terminated
filesystem pathname using bind(2). When the address of the socket
is returned by getsockname(2), getpeername(2), and accept(2), its
length is
offsetof(struct sockaddr_un, sun_path) + strlen(sun_path) + 1
and sun_path contains the null-terminated pathname.
- unnamed: A stream socket that has not been bound to a pathname
using bind(2) has no name. Likewise, the two sockets created by
socketpair(2) are unnamed. When the address of an unnamed socket
is returned by getsockname(2), getpeername(2), and accept(2), its
length is sizeof(sa_family_t), and sun_path should not be
inspected.
- abstract: an abstract socket address is distinguished by the fact
that sun_path[0] is a null byte (' '). The socket's address in
this namespace is given by the additional bytes in sun_path that
are covered by the specified length of the address structure.
(Null bytes in the name have no special significance.) The name
has no connection with filesystem pathnames. When the address of
an abstract socket is returned by getsockname(2), getpeername(2),
and accept(2), the returned addrlen is greater than
sizeof(sa_family_t) (i.e., greater than 2), and the name of the
socket is contained in the first (addrlen - sizeof(sa_family_t))
bytes of sun_path. The abstract socket namespace is a nonportable
Linux extension.
To list UD sockets:
# netstat -ap --unix Active UNIX domain sockets (servers and established) Proto RefCnt Flags Type State I-Node PID/Program name Path unix 2 [ ] DGRAM 5374 1/init /run/systemd/shutdownd unix 2 [ ACC ] STREAM LISTENING 11542 299/mcelog /var/run/mcelog-client unix 2 [ ACC ] SEQPACKET LISTENING 5398 1/init /run/udev/control unix 2 [ ACC ] STREAM LISTENING 5409 1/init /run/systemd/journal/stdout unix 4 [ ] DGRAM 5413 1/init /run/systemd/journal/socket unix 26 [ ] DGRAM 5417 1/init /dev/log unix 2 [ ACC ] STREAM LISTENING 8754 1/init /var/run/rpcbind.sock unix 2 [ ACC ] STREAM LISTENING 16462 655/gnome-session @/tmp/.ICE-unix/655 unix 2 [ ACC ] STREAM LISTENING 8765 1/init /var/run/pcscd/pcscd.comm unix 2 [ ACC ] STREAM LISTENING 10050 263/acpid /var/run/acpid.socket unix 2 [ ACC ] STREAM LISTENING 16712 653/gnome-keyring-d /run/user/fpm/keyring-YTwafF/pkcs11 unix 2 [ ACC ] STREAM LISTENING 16714 653/gnome-keyring-d /run/user/fpm/keyring-YTwafF/gpg unix 2 [ ACC ] STREAM LISTENING 16716 653/gnome-keyring-d /run/user/fpm/keyring-YTwafF/ssh unix 2 [ ACC ] STREAM LISTENING 8777 1/init /var/run/avahi-daemon/socket unix 2 [ ACC ] STREAM LISTENING 8789 1/init /var/run/cups/cups.sock unix 2 [ ACC ] STREAM LISTENING 12029 368/Xorg @/tmp/.X11-unix/X0 unix 2 [ ACC ] STREAM LISTENING 8798 1/init /var/run/dbus/system_bus_socket unix 2 [ ACC ] STREAM LISTENING 12690 372/bluetoothd /var/run/sdp unix 2 [ ACC ] STREAM LISTENING 16033 653/gnome-keyring-d /run/user/fpm/keyring-YTwafF/control unix 2 [ ACC ] STREAM LISTENING 12459 376/rpcbind /var/run/rpcbind.sock unix 2 [ ACC ] STREAM LISTENING 12030 368/Xorg /tmp/.X11-unix/X0 unix 2 [ ACC ] STREAM LISTENING 16770 864/pulseaudio /tmp/.esd-1000/socket unix 2 [ ACC ] STREAM LISTENING 16772 864/pulseaudio /home/fpm/.pulse/484969ea1695f6488ba1176f00000009-runtime/native unix 2 [ ACC ] STREAM LISTENING 14396 360/gdm-simple-slav @/tmp/gdm-session-WaQGMhfp unix 2 [ ACC ] STREAM LISTENING 15815 513/python /var/run/setroubleshoot/setroubleshoot_server unix 2 [ ACC ] STREAM LISTENING 16103 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 2 [ ACC ] STREAM LISTENING 16773 864/pulseaudio /home/fpm/.pulse/484969ea1695f6488ba1176f00000009-runtime/dbus-socket unix 2 [ ACC ] STREAM LISTENING 16463 655/gnome-session /tmp/.ICE-unix/655 unix 2 [ ] DGRAM 5334 1/init /run/systemd/notify unix 2 [ ACC ] STREAM LISTENING 5336 1/init /run/systemd/private unix 2 [ ACC ] STREAM LISTENING 11758 229/abrtd /var/run/abrt/abrt.socket unix 2 [ ] DGRAM 5360 1/init /run/systemd/journal/syslog unix 3 [ ] STREAM CONNECTED 15171 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 11655 313/avahi-daemon: c unix 3 [ ] STREAM CONNECTED 16747 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16410 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18160 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17885 984/evolution-alarm unix 2 [ ] DGRAM 12481 371/modem-manager unix 3 [ ] STREAM CONNECTED 17995 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17771 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16598 653/gnome-keyring-d unix 3 [ ] STREAM CONNECTED 18187 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18437 875/cupsd unix 3 [ ] STREAM CONNECTED 16753 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16473 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17977 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17777 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18166 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17910 984/evolution-alarm unix 3 [ ] STREAM CONNECTED 18172 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17918 953/seapplet unix 3 [ ] STREAM CONNECTED 11811 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 18143 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 17986 1027/gconfd-2 unix 2 [ ] DGRAM 12449 372/bluetoothd unix 3 [ ] STREAM CONNECTED 16466 655/gnome-session unix 3 [ ] STREAM CONNECTED 15464 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 18301 1079/gnome-terminal unix 3 [ ] STREAM CONNECTED 16768 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17940 923/abrt-applet unix 3 [ ] STREAM CONNECTED 11654 259/avahi-daemon: r unix 3 [ ] STREAM CONNECTED 17943 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 11002 274/sedispatch unix 3 [ ] STREAM CONNECTED 62649 1250/su unix 3 [ ] STREAM CONNECTED 18295 1079/gnome-terminal unix 3 [ ] STREAM CONNECTED 18198 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17792 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18297 1079/gnome-terminal unix 3 [ ] STREAM CONNECTED 16751 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16743 864/pulseaudio unix 3 [ ] STREAM CONNECTED 15377 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 17589 923/abrt-applet unix 3 [ ] STREAM CONNECTED 9809 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 17243 896/colord unix 3 [ ] STREAM CONNECTED 17099 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17002 877/gsd-printer unix 3 [ ] STREAM CONNECTED 9883 259/avahi-daemon: r unix 2 [ ] DGRAM 27522 1477/sendmail: Queu unix 3 [ ] STREAM CONNECTED 16746 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 14031 360/gdm-simple-slav unix 3 [ ] STREAM CONNECTED 10204 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 18108 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16225 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 11814 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17406 902/gnome-shell unix 3 [ ] STREAM CONNECTED 11860 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17404 864/pulseaudio /home/fpm/.pulse/484969ea1695f6488ba1176f00000009-runtime/native unix 3 [ ] STREAM CONNECTED 17261 902/gnome-shell unix 3 [ ] STREAM CONNECTED 17114 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16813 655/gnome-session unix 2 [ ] DGRAM 15884 359/polkitd unix 3 [ ] STREAM CONNECTED 18215 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 15846 622/gdm-session-wor unix 3 [ ] STREAM CONNECTED 12667 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 11973 360/gdm-simple-slav unix 3 [ ] STREAM CONNECTED 11264 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 18064 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17120 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 15670 304/dbus-daemon /var/run/dbus/system_bus_socket unix 2 [ ] DGRAM 11752 229/abrtd unix 3 [ ] STREAM CONNECTED 17754 915/tracker-store unix 3 [ ] STREAM CONNECTED 18293 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 16170 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 13944 449/VBoxService unix 3 [ ] STREAM CONNECTED 18061 917/deja-dup-monito unix 3 [ ] STREAM CONNECTED 17396 902/gnome-shell unix 3 [ ] STREAM CONNECTED 16811 864/pulseaudio unix 3 [ ] STREAM CONNECTED 10130 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 16163 729/imsettings-daem unix 3 [ ] STREAM CONNECTED 17739 923/abrt-applet unix 3 [ ] STREAM CONNECTED 16823 653/gnome-keyring-d /run/user/fpm/keyring-YTwafF/pkcs11 unix 3 [ ] STREAM CONNECTED 11804 304/dbus-daemon unix 3 [ ] STREAM CONNECTED 17886 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 17770 915/tracker-store unix 3 [ ] STREAM CONNECTED 16573 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 15170 544/upowerd unix 2 [ ] DGRAM 11642 265/systemd-logind unix 3 [ ] STREAM CONNECTED 16754 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 18195 902/gnome-shell unix 3 [ ] STREAM CONNECTED 18159 1052/mission-contro unix 3 [ ] STREAM CONNECTED 17994 990/gnome-screensav unix 3 [ ] STREAM CONNECTED 17776 934/nm-applet unix 3 [ ] STREAM CONNECTED 17911 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16724 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16472 655/gnome-session unix 3 [ ] STREAM CONNECTED 11545 1/init unix 3 [ ] STREAM CONNECTED 17976 934/nm-applet unix 3 [ ] STREAM CONNECTED 16405 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18184 1056/goa-daemon unix 3 [ ] STREAM CONNECTED 18165 1052/mission-contro unix 3 [ ] STREAM CONNECTED 18304 1085/gnome-pty-help unix 3 [ ] STREAM CONNECTED 16458 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 16467 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 18200 916/tracker-miner-f unix 3 [ ] STREAM CONNECTED 17791 983/dconf-service unix 3 [ ] STREAM CONNECTED 16572 653/gnome-keyring-d unix 3 [ ] STREAM CONNECTED 15463 594/rtkit-daemon unix 3 [ ] STREAM CONNECTED 12608 372/bluetoothd unix 3 [ ] STREAM CONNECTED 18300 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 2 [ ] DGRAM 62683 1250/su unix 3 [ ] STREAM CONNECTED 18142 1050/gnome-shell-ca unix 3 [ ] STREAM CONNECTED 17919 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17987 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16392 827/VBoxClient unix 3 [ ] STREAM CONNECTED 16752 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 15375 594/rtkit-daemon unix 3 [ ] STREAM CONNECTED 18296 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 2 [ ] DGRAM 16735 864/pulseaudio unix 3 [ ] STREAM CONNECTED 11663 265/systemd-logind unix 3 [ ] STREAM CONNECTED 17942 923/abrt-applet unix 2 [ ] DGRAM 10537 246/audispd unix 3 [ ] STREAM CONNECTED 17941 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17244 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17107 884/gvfs-udisks2-vo unix 3 [ ] STREAM CONNECTED 17003 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 15849 360/gdm-simple-slav @/tmp/gdm-session-WaQGMhfp unix 2 [ ] DGRAM 9814 263/acpid unix 3 [ ] STREAM CONNECTED 17590 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 14474 498/accounts-daemon unix 3 [ ] STREAM CONNECTED 9579 246/audispd unix 3 [ ] STREAM CONNECTED 10276 266/system-setup-ke unix 3 [ ] STREAM CONNECTED 16814 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16164 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 14032 368/Xorg @/tmp/.X11-unix/X0 unix 2 [ ] DGRAM 11871 304/dbus-daemon unix 3 [ ] STREAM CONNECTED 18107 902/gnome-shell unix 3 [ ] STREAM CONNECTED 17262 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17199 896/colord unix 3 [ ] STREAM CONNECTED 17019 884/gvfs-udisks2-vo unix 3 [ ] STREAM CONNECTED 14475 304/dbus-daemon /var/run/dbus/system_bus_socket unix 2 [ ] DGRAM 9581 226/auditd unix 3 [ ] STREAM CONNECTED 17407 655/gnome-session @/tmp/.ICE-unix/655 unix 3 [ ] STREAM CONNECTED 11475 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 18214 902/gnome-shell unix 3 [ ] STREAM CONNECTED 12886 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 16169 732/gvfsd unix 3 [ ] STREAM CONNECTED 11803 304/dbus-daemon unix 3 [ ] STREAM CONNECTED 18063 917/deja-dup-monito unix 3 [ ] STREAM CONNECTED 17020 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16788 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 11974 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17755 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18292 1079/gnome-terminal unix 3 [ ] STREAM CONNECTED 16113 667/dbus-daemon unix 3 [ ] STREAM CONNECTED 16160 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18062 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16821 864/pulseaudio /home/fpm/.pulse/484969ea1695f6488ba1176f00000009-runtime/native unix 3 [ ] STREAM CONNECTED 17740 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17128 895/gvfs-gphoto2-vo unix 3 [ ] STREAM CONNECTED 15162 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 17397 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 11213 292/crond unix 3 [ ] STREAM CONNECTED 18185 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16822 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 15177 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 11883 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17989 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17888 990/gnome-screensav unix 3 [ ] STREAM CONNECTED 17768 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16159 729/imsettings-daem unix 3 [ ] STREAM CONNECTED 16723 864/pulseaudio unix 2 [ ] DGRAM 18170 1056/goa-daemon unix 3 [ ] STREAM CONNECTED 16755 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16494 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16416 827/VBoxClient unix 3 [ ] STREAM CONNECTED 11805 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 18203 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 18016 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 12490 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17912 990/gnome-screensav unix 3 [ ] STREAM CONNECTED 62650 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 18201 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18148 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17975 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17787 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 2 [ ] DGRAM 15462 594/rtkit-daemon unix 3 [ ] STREAM CONNECTED 18303 1079/gnome-terminal unix 3 [ ] STREAM CONNECTED 18004 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 17965 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17853 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16406 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18196 864/pulseaudio /home/fpm/.pulse/484969ea1695f6488ba1176f00000009-runtime/native unix 3 [ ] STREAM CONNECTED 18154 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18299 1079/gnome-terminal unix 3 [ ] STREAM CONNECTED 16719 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 16460 655/gnome-session unix 3 [ ] STREAM CONNECTED 11808 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 14473 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 18141 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 2 [ ] DGRAM 6303 1/init unix 3 [ ] DGRAM 6451 66/udevd unix 3 [ ] STREAM CONNECTED 17671 923/abrt-applet unix 3 [ ] STREAM CONNECTED 16362 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 9580 226/auditd unix 3 [ ] STREAM CONNECTED 17251 902/gnome-shell unix 2 [ ] DGRAM 17091 886/udisksd unix 3 [ ] STREAM CONNECTED 17012 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 15848 622/gdm-session-wor unix 3 [ ] STREAM CONNECTED 15840 622/gdm-session-wor unix 3 [ ] STREAM CONNECTED 11859 264/NetworkManager unix 3 [ ] STREAM CONNECTED 18241 902/gnome-shell unix 3 [ ] STREAM CONNECTED 12881 400/sshd unix 3 [ ] STREAM CONNECTED 9810 56/systemd-journald /run/systemd/journal/stdout unix 2 [ ] DGRAM 6539 66/udevd unix 3 [ ] STREAM CONNECTED 18068 653/gnome-keyring-d /run/user/fpm/keyring-YTwafF/pkcs11 unix 3 [ ] STREAM CONNECTED 10277 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 16227 734/gvfs-fuse-daemo unix 3 [ ] STREAM CONNECTED 11537 304/dbus-daemon unix 3 [ ] STREAM CONNECTED 17864 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 9884 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 17331 906/colord-sane unix 3 [ ] STREAM CONNECTED 17108 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16891 875/cupsd unix 3 [ ] STREAM CONNECTED 16787 864/pulseaudio unix 3 [ ] STREAM CONNECTED 14617 274/sedispatch unix 3 [ ] STREAM CONNECTED 16892 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 16086 368/Xorg @/tmp/.X11-unix/X0 unix 2 [ ] DGRAM 12970 405/rpc.statd unix 3 [ ] STREAM CONNECTED 18058 917/deja-dup-monito unix 3 [ ] STREAM CONNECTED 17395 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17200 56/systemd-journald /run/systemd/journal/stdout unix 2 [ ] DGRAM 15662 513/python unix 2 [ ] DGRAM 16051 360/gdm-simple-slav unix 3 [ ] STREAM CONNECTED 11931 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16229 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 11474 299/mcelog unix 2 [ ] DGRAM 16015 622/gdm-session-wor unix 3 [ ] STREAM CONNECTED 11799 264/NetworkManager unix 3 [ ] STREAM CONNECTED 14472 498/accounts-daemon unix 3 [ ] STREAM CONNECTED 18019 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17129 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16820 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 15161 544/upowerd unix 3 [ ] STREAM CONNECTED 16380 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18009 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 18186 1050/gnome-shell-ca unix 3 [ ] STREAM CONNECTED 16393 829/VBoxClient unix 3 [ ] STREAM CONNECTED 16461 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17889 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 17767 916/tracker-miner-f unix 3 [ ] STREAM CONNECTED 15175 544/upowerd unix 3 [ ] STREAM CONNECTED 11882 295/gdm-binary unix 3 [ ] STREAM CONNECTED 16750 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 16599 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 17988 984/evolution-alarm unix 2 [ ] DGRAM 13794 292/crond unix 3 [ ] STREAM CONNECTED 18171 1056/goa-daemon unix 3 [ ] STREAM CONNECTED 18438 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16457 655/gnome-session unix 3 [ ] STREAM CONNECTED 18007 934/nm-applet unix 3 [ ] STREAM CONNECTED 17913 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16767 864/pulseaudio unix 3 [ ] STREAM CONNECTED 16493 655/gnome-session unix 2 [ ] DGRAM 11651 259/avahi-daemon: r unix 3 [ ] STREAM CONNECTED 16744 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 16417 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18302 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 11666 259/avahi-daemon: r unix 3 [ ] STREAM CONNECTED 18147 1050/gnome-shell-ca unix 3 [ ] STREAM CONNECTED 17974 1027/gconfd-2 unix 3 [ ] STREAM CONNECTED 11003 246/audispd unix 3 [ ] STREAM CONNECTED 18202 916/tracker-miner-f unix 3 [ ] STREAM CONNECTED 17786 916/tracker-miner-f unix 3 [ ] STREAM CONNECTED 18298 655/gnome-session @/tmp/.ICE-unix/655 unix 2 [ ] DGRAM 27095 1451/sendmail: acce unix 3 [ ] STREAM CONNECTED 16720 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18003 990/gnome-screensav unix 3 [ ] STREAM CONNECTED 17964 984/evolution-alarm unix 3 [ ] STREAM CONNECTED 12489 371/modem-manager unix 3 [ ] STREAM CONNECTED 18153 1052/mission-contro unix 3 [ ] STREAM CONNECTED 17852 934/nm-applet unix 3 [ ] STREAM CONNECTED 18197 902/gnome-shell unix 3 [ ] STREAM CONNECTED 15841 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 10203 265/systemd-logind unix 3 [ ] DGRAM 6452 66/udevd unix 2 [ ] DGRAM 26795 1430/dhclient unix 3 [ ] STREAM CONNECTED 16361 810/VBoxClient unix 3 [ ] STREAM CONNECTED 18140 902/gnome-shell unix 3 [ ] STREAM CONNECTED 17252 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 17098 886/udisksd unix 3 [ ] STREAM CONNECTED 17011 877/gsd-printer unix 3 [ ] STREAM CONNECTED 15847 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16114 666/dbus-launch unix 3 [ ] STREAM CONNECTED 17672 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 9805 254/abrt-watch-log unix 3 [ ] STREAM CONNECTED 9733 253/abrt-watch-log unix 3 [ ] STREAM CONNECTED 18242 864/pulseaudio /home/fpm/.pulse/484969ea1695f6488ba1176f00000009-runtime/native unix 3 [ ] STREAM CONNECTED 16224 734/gvfs-fuse-daemo unix 3 [ ] STREAM CONNECTED 13945 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16115 368/Xorg @/tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 18067 902/gnome-shell unix 3 [ ] STREAM CONNECTED 17338 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 17113 884/gvfs-udisks2-vo unix 3 [ ] STREAM CONNECTED 14618 304/dbus-daemon /var/run/dbus/system_bus_socket unix 3 [ ] STREAM CONNECTED 16085 666/dbus-launch unix 3 [ ] STREAM CONNECTED 17863 953/seapplet unix 3 [ ] STREAM CONNECTED 18008 990/gnome-screensav unix 3 [ ] STREAM CONNECTED 17119 892/gvfs-afc-volume unix 3 [ ] STREAM CONNECTED 17013 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 11930 359/polkitd unix 3 [ ] STREAM CONNECTED 16379 820/VBoxClient unix 3 [ ] STREAM CONNECTED 11539 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 18059 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 2 [ ] STREAM CONNECTED 16905 861/gnome-settings- unix 3 [ ] STREAM CONNECTED 15669 513/python unix 3 [ ] STREAM CONNECTED 12179 56/systemd-journald /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 17394 902/gnome-shell unix 3 [ ] STREAM CONNECTED 12178 372/bluetoothd unix 3 [ ] STREAM CONNECTED 17403 902/gnome-shell unix 3 [ ] STREAM CONNECTED 17014 667/dbus-daemon @/tmp/dbus-ZVFyq1nvzA unix 3 [ ] STREAM CONNECTED 10129 264/NetworkManager unix 3 [ ] STREAM CONNECTED 16383 820/VBoxClient unix 2 [ ] DGRAM 11792 264/NetworkManager unix 3 [ ] STREAM CONNECTED 16112 667/dbus-daemon unix 3 [ ] STREAM CONNECTED 18018 934/nm-applet unix 3 [ ] STREAM CONNECTED 16812 655/gnome-session @/tmp/.ICE-unix/655
The above listing is from a Fedora 17 system. As you can see, UD sockets are used extensively on modern systems.
