求解 Linux 对本地主机名的解析方式

• 資深大佬 : D0n9

  先走 /etc/hosts

• 主 資深大佬 : enlightment

  /etc/hosts 并里没有单独对 xxxa 做任何解析

• 資深大佬 : 3dwelcome

  主机名解析底层就是调用 gethostbyname，你说为什么不对应第二个 ip，理论上应该对应 0.0.0.0，绑定所有的本机 ip，但 linux 程序员就是写了获取回来的第一个 ip，你也没办法。

• 主 資深大佬 : enlightment

  @3dwelcome 这个是内核里写的逻辑吗？

• 資深大佬 : 3dwelcome

  严格来说不算内核，就算是个提供给程序的调用库。

• 資深大佬 : julyclyde

  strace 一下 ping 看看？

• 資深大佬 : lenqu

  traceroute 一下，看看那走的节点

• 資深大佬 : huangmingyou

  man 5 nsswitch.conf

• 資深大佬 : huangmingyou

  # /etc/nsswitch.conf
  #
  # Example configuration of GNU Name Service Switch functionality.
  # If you have the `glibc-doc-reference’ and `info’ packages installed, try:
  # `info libc “Name Service Switch”‘ for information about this file.

  passwd: compat
  group: compat
  shadow: compat
  gshadow: files

  hosts: files mdns4_minimal [NOTFOUND=return] dns
  networks: files

  protocols: db files
  services: db files
  ethers: db files
  rpc: db files

  netgroup: nis

• 資深大佬 : targetFree

  @3dwelcome 好像 gethostbyname 已被 getaddrinfo 替代

• 資深大佬 : baobao1270

  systemd resolved?

• 主 資深大佬 : enlightment

  @julyclyde
  [[email protected] ~]# strace -f -e open ping cent7.550gtmp
  open(“/etc/ld.so.cache”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libcap.so.2”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libidn.so.11”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libcrypto.so.10”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libresolv.so.2”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libm.so.6”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libc.so.6”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libattr.so.1”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libdl.so.2”, O_RDONLY|O_CLOEXEC) = 3
  open(“/lib64/libz.so.1”, O_RDONLY|O_CLOEXEC) = 3
  open(“/etc/pki/tls/legacy-settings”, O_RDONLY) = -1 ENOENT (No such file or directory)
  open(“/usr/lib/locale/locale-archive”, O_RDONLY|O_CLOEXEC) = 3
  open(“/etc/resolv.conf”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/nsswitch.conf”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/ld.so.cache”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/libnss_files.so.2”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/host.conf”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/hosts”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/ld.so.cache”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/libnss_dns.so.2”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/ld.so.cache”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/libnss_myhostname.so.2”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/librt.so.1”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/libdw.so.1”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/libgcc_s.so.1”, O_RDONLY|O_CLOEXEC) = 4
  open(“/lib64/libpthread.so.0”, O_RDONLY|O_CLOEXEC) = 4
  open(“/usr/lib64/elfutils/tls/x86_64/libelf.so.1”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  open(“/usr/lib64/elfutils/tls/libelf.so.1”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  open(“/usr/lib64/elfutils/x86_64/libelf.so.1”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  open(“/usr/lib64/elfutils/libelf.so.1”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  open(“/lib64/libelf.so.1”, O_RDONLY|O_CLOEXEC) = 4
  open(“/usr/lib64/elfutils/liblzma.so.5”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  open(“/lib64/liblzma.so.5”, O_RDONLY|O_CLOEXEC) = 4
  open(“/usr/lib64/elfutils/libbz2.so.1”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  open(“/lib64/libbz2.so.1”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/hosts”, O_RDONLY|O_CLOEXEC) = 4
  open(“/etc/gai.conf”, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
  PING cent7.550gtmp (10.0.182.120) 56(84) bytes of data.
  open(“/etc/hosts”, O_RDONLY|O_CLOEXEC) = 4
  64 bytes from cent7.550gtmp (10.0.112.1): icmp_seq=1 ttl=64 time=0.050 ms
  64 bytes from cent7.550gtmp (10.0.112.1): icmp_seq=2 ttl=64 time=0.104 ms
  64 bytes from cent7.550gtmp (10.0.112.1): icmp_seq=3 ttl=64 time=0.049 ms
  64 bytes from cent7.550gtmp (10.0.112.1): icmp_seq=4 ttl=64 time=0.047 ms
  ^C
  strace: Process 56574 detached