Socket units

Socket units are used to manage:

• IPC sockets;
• network sockets;
• filesystem FIFO;

A socket unit is paired with a matching service.

Systemd socket addresses

If the address starts with /, a file system AF_UNIX socket is used. If the address starts with @ an abstract namespace AF_UNIX socket is used. If the address string is v.w.x.y:z it is interpreted as IPv4 address. If the address string is [x]:y it is interpreted as IPv6 address.

• Accept= :
  • yes : the service is started at each connection, and the connection socket is passet to it.
  • no : the service is started once, and the listen socket is passed to it.

Socket types

• ListenStream=: specifies the adress to listen on for a SOCK_STREAM; can be defined multiple times;
• ListenDatagram=: specifies the address to listen on for a SOCK_DGRAM; can be defined multiple times;
• ListenSequentialPacket=: specifies the address to listen on for a SOCK_SEQPACKET; can be defined multiple times;
• ListenFIFO=: an absolute path pointing to a file system FIFO;
• ListenSpecial=: similar to ListenFIFO= but used for listening to character devices and special files like those in /sys and /proc;
• ListenNetlink=: ??
• ListenMessageQueue=: ??
• ListenUSBFunction=: ??

Network socket options

For AF_INET and AF_INET6 sockets;

• SocketProtocol:

  • udplite;
  • sctp;
  • mptcp;

• BindIPv6Only=: controls the IPV6_V6ONLY option:

  • default: uses the system wide default setting (default both);
  • both;
  • ipv6-only:

• Backlog=

• BindToDevice=: specifies a network interface for the socket and controls the SO_BINDTODEVICE socket option.

File system socket options

For AF_UNIX sockets and FIFOs.

• SocketUser=: user owner of the created unix sockets and fifo nodes;

• SocketGroup=: group owner of the created unix socket and fifo nodes;

• SocketMode=: access mode of the created unix socket and fifo nodes; defaults to 0666

• DirectoryMode: access mode of the created directories, defaults to 0755

• MaxConnections=

• MaxConnectionsPerSource=

• KeepAlive=: controls the SO_KEEPALIVE option;

• KeepAliveTimeSec=: controls the TCP_KEEPIDLE option;

• KeepAliveIntervalSec=: controls the TCP_KEEPINTVL option;

• KeepAliveProbes=: controls the TCP_KEEPCNT option;

• NoDelay=: controls the TCP_NODELAY option;

• Priority=: controls the SO_PRIORIY option;

• DeferAcceptSec=: ??

• ReceiveBuffer=: controls the SO_RCVBUF option;

• SendBuffer=: controls the SO_SNDBUF option;

• IPTOS=: controls the IP_TOS option;

• Mark=: controls the SO_MARK option;

• ReusePort=: controls the SO_REUSEPORT option;

• PipeSize=: controls the pipe buffer size of FIFOs;

• Broadcast=: controls the SO_BROADCAST socket (default to false);

• PassCredentials=

• PassSecurity=

• PassPacketInfo=

• Timestamping=: controls the SO_TIMESTAMP or SO_TIMESTAMPNS

  • off:
  • us:
  • ns: