57.3. Datagram Sockets in the UNIX Domain

In the generic description of datagram sockets that we provided in Section 56.6, we stated that communication using datagram sockets is unreliable. This is the case for datagrams transferred over a network. However, for UNIX domain sockets, datagram transmission is carried out within the kernel, and is reliable. All messages are delivered in order and unduplicated.

57.3.1.

57.3.1.1. Maximum datagram size for UNIX domain datagram sockets

SUSv3 doesn’t specify a maximum size for datagrams sent via a UNIX domain socket. On Linux, we can send quite large datagrams. The limits are controlled via the SO_SNDBUF socket option and various /proc files, as described in the socket(7) manual page. However, some other UNIX implementations impose lower limits, such as 2048 bytes. Portable applications employing UNIX domain datagram sockets should consider imposing a low upper limit on the size of datagrams used.