1. 什麼是unix domain socket

2. 有兩種方法，第一種是通過猜測，第二種是debug linux核心

第一種方法的示例：

[[email protected] ipc]$  /usr/sbin/lsof -p 31854
COMMAND   PID     USER   FD   TYPE             DEVICE SIZE/OFF      NODE NAME
server  31854 test  cwd    DIR               0,26     4096  15746636 /home/test/workspace_ipc/ipc
server  31854 test  rtd    DIR                8,2     4096         2 /
server  31854 test  txt    REG               0,26     8702  15746641 /home/test/workspace_ipc/ipc/server
server  31854 test  mem    REG                8,2   144776  52035586 /lib64/ld-2.5.so
server  31854 test  mem    REG                8,2  1722328  52035588 /lib64/libc-2.5.so
server  31854 test    0u   CHR              136,2      0t0         4 /dev/pts/2
server  31854 test    1u   CHR              136,2      0t0         4 /dev/pts/2
server  31854 test    2u   CHR              136,2      0t0         4 /dev/pts/2
server  31854 test    3u  unix 0xffff8101c8d39180      0t0 650000043 ./socket
[
 
[email protected] ipc]$  /usr/sbin/lsof -p 32028
COMMAND   PID     USER   FD   TYPE             DEVICE SIZE/OFF      NODE NAME
client  32028 test  cwd    DIR               0,26     4096  15746636 /home/test/workspace_ipc/ipc
client  32028 test  rtd    DIR                8,2     4096         2 /
client  32028 test  txt    REG               0,26     8199  15746715 /home/test/workspace_ipc/ipc/client
client  32028 test  mem    REG                8,2   144776  52035586 /lib64/ld-2.5.so
client  32028 test  mem    REG                8,2  1722328  52035588 /lib64/libc-2.5.so
client  32028 test    0u   CHR              136,2      0t0         4 /dev/pts/2
client  32028 test    1u   CHR              136,2      0t0         4 /dev/pts/2
client  32028 test    2u   CHR              136,2      0t0         4 /dev/pts/2
client  32028 test    3u  unix 0xffff810010eaa080      0t0 650002435 socket
[
 
[email protected] ipc]$ netstat -na | grep 65000
unix  2      [ ACC ]     STREAM     LISTENING     650000043 ./socket
unix  3      [ ]         STREAM     CONNECTED     650002215 ./socket
unix  3      [ ]         STREAM     CONNECTED     650002435

第二種方法：

不能直接獲得對端的資訊的原因是，因linux核心對user space是不可見的。

The number shown in /proc/$pid/fd/$fd is the socket's inode number in the virtual socket filesystem. When you create a pipe or socket pair, each end successively receives an inode number. The numbers are attributed sequentially, so there is a high probability that the numbers differ by 1, but this is not guaranteed (either because the first socket was N and N+1 was already in use due to wrapping, or because some other thread was scheduled between the two inode allocations and that thread created some inodes too).