resolv.conf(5) File Formats Manual resolv.conf(5) resolv.conf - /etc/resolv.conf resolver C (DNS) . . . DNS trust-ad . . : nameserver IP IPv4 ( ) IPv6 ( ) RFC 2373. MAXNS ( 3 ) . . nameserver . ( .) search . . gethostname(2) '.'. '.' . search . ndots ( 1) . options ndots:n DNS . . search . glibc 2.25 256 . glibc 2.26 . domain search . sortlist gethostbyname(3). IP . . IP . 10 . : sortlist 130.155.160.0/255.255.240.0 130.155.0.0 options . options ... option : debug RES_DEBUG _res.options ( glibc resolver(3)). ndots:n res_query(3) ( resolver(3)) . n 1 . 15. timeout:n . API API . RES_TIMEOUT ( 5 ). 30. attempts:n . RES_DFLRETRY ( 2 ). 5. rotate RES_ROTATE _res.options . . no-aaaa ( glibc 2.36) RES_NOAAAA _res.options AAAA AAAA NSS getaddrinfo(3). DNS: IPv6 hosts(5) getaddrinfo(3) AI_PASSIVE IPv6 IPv6 . (NXDOMAIN) AAAA A. DNS AAAA . EDNS0 DNSSEC . no-check-names RES_NOCHECKNAME _res.options BIND (_) ASCII . inet6 RES_USE_INET6 _res.options. AAAA A gethostbyname(3) IPv4 " " IPv6 AAAA A. glibc 2.25 getaddrinfo(3) gethostbyname(3). ip6-bytestring ( glibc 2.3.4 glibc 2.24) RES_USEBSTRING _res.options. IPv6 RFC 2673 ( ) nibble. glibc 2.25 DNS . ip6-dotint/no-ip6-dotint (glibc 2.3.4 glibc 2.24) / RES_NOIP6DOTINT _res.options. (ip6-dotint) IPv6 ip6.int () (no-ip6-dotint) IPv6 ip6.arpa . glibc 2.24 no-ip6-dotint . ip6-dotint glibc 2.25. edns0 ( glibc 2.6) RES_USE_EDNS0 _res.options. DNS RFC 2671. single-request ( glibc 2.10) RES_SNGLKUP _res.options. glibc IPv4 IPv6 glibc 2.9. DNS . glibc IPv6 IPv4 ( ). single-request-reopen ( glibc 2.9) RES_SNGLKUPREOP _res.options. A AAAA. . . . no-tld-query ( glibc 2.14) RES_NOTLDQUERY _res.options. res_nsearch() (TLD). "localhost" TLD localhost . RES_DEFNAMES RES_DNSRCH. use-vc ( glibc 2.14) RES_USEVC _res.options. TCP DNS. no-reload ( glibc 2.26) RES_NORELOAD _res.options. . trust-ad ( glibc 2.31) RES_TRUSTAD _res.options. AD . AD DNSSEC. AD DNSSEC . trust-ad AD DNS ( AD) AD . AD . AD trust-ad . glibc 2.30 AD . search resolv.conf LOCALDOMAIN . options resolv.conf RES_OPTIONS options. ( nameserver) . . (;) (#) . /etc/resolv.conf gethostbyname(3) resolver(3) host.conf(5) hosts(5) nsswitch.conf(5) hostname(7) named(8) BIND 3 . . : . 4th Berkeley Distribution 21 2025 resolv.conf(5)