Файл hosts: сопоставление имен хостов и IP-адресов

Computer configuration file to map hostnames to IP addresses

The computer file hosts is an operating system file that maps hostnames to IP addresses. It is a plain text file. Originally a file named HOSTS. TXT was manually maintained and made available via file sharing by Stanford Research Institute for the ARPANET membership, containing the hostnames and address of hosts as contributed for inclusion by member organizations. The Domain Name System, first described in 1983 and implemented in 1984, automated the publication process and provided instantaneous and dynamic hostname resolution in the rapidly growing network. In modern operating systems, the hosts file remains an alternative name resolution mechanism, configurable often as part of facilities such as the Name Service Switch as either the primary method or as a fallback method.

The hosts file is one of several system facilities that assists in addressing network nodes in a computer network. It is a common part of an operating system's Internet Protocol (IP) implementation, and serves the function of translating human friendly hostnames into numeric protocol addresses, called IP addresses, that identify and locate a host in an IP network. In some operating systems, the contents of the hosts file is used preferentially to other name resolution methods, such as the Domain Name System (DNS), but many systems implement name service switches, e. g., nsswitch. conf for Linux and Unix, to provide customization. Unlike remote DNS resolvers, the hosts file is under the direct control of the local computer's administrator.

The location of the hosts file in the file system hierarchy varies by operating system. It is usually named hosts, without an extension. Operating System Version(s) Location Unix, Unix like, POSIX /etc/hostsMicrosoft Windows 3.1 %WinDir%\HOSTS 95, 98, ME %WinDir%\hosts NT, 2000, XP, 2003, Vista,2008, 7, 2012, 8, 10, 11 %SystemRoot%\System32\drivers\etc\hosts Windows Mobile, Windows Phone Registry key under HKEY LOCAL MACHINE\Comm\Tcpip\Hosts Apple Macintosh 9 and earlier Preferences or System folder Mac OS X 10.0–10.1.5 (Added through NetInfo or niload) Mac OS X 10.2 and newer /etc/hosts (a symbolic link to /private/etc/hosts) Haiku /system/settings/network/hosts OpenVMS UCX UCX$HOST TCPware TCPIP$HOST RISC OS 3.7, 5 !Boot. Resources.!Internet. files. Hosts later boot sequence !Boot. Choices. Hardware. Disabled. Internet. Files. Hosts

The ARPANET, the predecessor of the Internet, had no distributed host name database. Each network node maintained its own map of the network nodes as needed and assigned them names that were memorable to the users of the system. There was no method for ensuring that all references to a given node in a network were using the same name, nor was there a way to read the hosts file of another computer to automatically obtain a copy. The small size of the ARPANET kept the administrative overhead small to maintain an accurate hosts file. Network nodes typically had one address and could have many names. As local area TCP/IP computer networks gained popularity, however, the maintenance of hosts files became a larger burden on system administrators as networks and network nodes were being added to the system with increasing frequency. Standardization efforts, such as the format specification of the file HOSTS. TXT in RFC 952, and distribution protocols, e. g., the hostname server described in RFC 953, helped with these problems, but the centralized and monolithic nature of hosts files eventually necessitated the creation of the distributed Domain Name System (DNS). On some old systems a file named networks is present that is similar to a hosts file, containing names of networks.

In its function of resolving host names, the hosts file may be used to define any hostname or domain name for use in the local system. Redirecting local domains Some web service and intranet developers and administrators define locally defined domains in a LAN for various purposes, such as accessing the company's internal resources or to test local websites in development. Internet resource blocking Entries in the hosts file may be used to block online advertising, or the domains of known malicious resources and servers that contain spyware, adware, and other malware. This may be achieved by adding entries for those sites to redirect requests to another address that does not exist or to a harmless destination such as the local machine. Commercial software applications may be used to populate the hosts file with entries of known undesirable Internet resources automatically. In addition, user created hosts files which block nuisance servers are publicly available. Fravia described these files variously as "scrolls", "precious", and "powerful" in his anti advertisement pages, where this usage of hosts was first published.

The hosts file may present an attack vector for malicious software. The file may be modified, for example, by adware, computer viruses, or trojan horse software to redirect traffic from the intended destination to sites hosting malicious or unwanted content. The widespread computer worm Mydoom. B blocked users from visiting sites about computer security and antivirus software and also affected access from the compromised computer to the Microsoft Windows Update website. In some cases, malware has modified the library responsible for loading the hosts file in order to redirect it to a file it is able to control freely.