How to read netstat output
tcp 0 0 192.168.22.6:55017 www.oreillynet.com:www ESTABLISHED
^ ^ ^ ^ ^ ^ ^ ^ | | | | | | | | | | | | port remote port Connection | | | your machine server State | | bytes in send queue | Bytes in recive queue | type of connection
Connection State can be
StateDescription
| LISTEN | accepting connections |
| ESTABLISHED | connection up and passing data |
| SYN_SENT | TCP; session has been requested by us; waiting for reply from remote endpoint |
| SYN_RECV | TCP; session has been requested by a remote endpoint for a socket on which we were listening |
| LAST_ACK | TCP; our socket is closed; remote endpoint has also shut down; we are waiting for a final acknowledgement |
| CLOSE_WAIT | TCP; remote endpoint has shut down; the kernel is waiting for the application to close the socket |
| TIME_WAIT | TCP; socket is waiting after closing for any packets left on the network |
| CLOSED | socket is not being used (FIXME. What does mean?) |
| CLOSING | TCP; our socket is shut down; remote endpoint is shut down; not all data has been sent |
| FIN_WAIT1 | TCP; our socket has closed; we are in the process of tearing down the connection |
| FIN_WAIT2 | TCP; the connection has been closed; our socket is waiting for the remote endpoint to shut down |
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ACC ] STREAM LISTENING 21775 /tmp/.X11-unix/X0
unix 2 [ ACC ] STREAM LISTENING 22279 /var/run/sock.sock
| | | | | | |
| | | Stream State Inode disk file
| | Flags
| Reference Count
Protocol
A Unix domain socket (UDS) or IPC socket (inter-process communication socket) is a virtual socket, similar to an internet socket that is used in POSIX operating systems for inter-process communication. The correct standard POSIX term is POSIX Local IPC Sockets.
These connections appear as byte streams, much like network connections, but all data remains within the local computer.
In addition to sending data, processes can send file descriptors across a Unix domain socket connection using the sendmsg() and recvmsg() system calls.
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