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enlightment
V2EX  ›  Linux

求解 Linux 对本地主机名的解析方式

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  •   enlightment · 122 天前 · 1156 次点击
    这是一个创建于 122 天前的主题,其中的信息可能已经有所发展或是发生改变。
    centos7 本机的 hostname 为 xxxa
    吃时 ping xxxa 解析到了 eth1 对应的 ip,这个解析走的是哪里的 dns ?为什么会解析到 eth1 的 ip 而不是 eth2 eth3 的?
    12 条回复    2020-11-03 14:22:53 +08:00
    D0n9
        1
    D0n9   122 天前
    先走 /etc/hosts
    enlightment
        2
    enlightment   122 天前
    /etc/hosts 并里没有单独对 xxxa 做任何解析
    3dwelcome
        3
    3dwelcome   122 天前 via Android   ❤️ 1
    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。
    enlightment
        4
    enlightment   122 天前
    @3dwelcome 这个是内核里写的逻辑吗?
    3dwelcome
        5
    3dwelcome   122 天前 via Android
    严格来说不算内核,就算是个提供给程序的调用库。
    julyclyde
        6
    julyclyde   122 天前
    strace 一下 ping 看看?
    lenqu
        7
    lenqu   122 天前
    traceroute 一下,看看那走的节点
    huangmingyou
        8
    huangmingyou   122 天前
    man 5 nsswitch.conf
    huangmingyou
        9
    huangmingyou   122 天前
    # /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
    targetFree
        10
    targetFree   122 天前
    @3dwelcome 好像 gethostbyname 已被 getaddrinfo 替代
    baobao1270
        11
    baobao1270   121 天前 via Android
    systemd resolved?
    enlightment
        12
    enlightment   121 天前
    @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
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