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man pages section 5: File Formats

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Updated: Wednesday, February 9, 2022



ethers - Ethernet address to hostname database


The ethers file is a local source of information about the (48–bit) Ethernet addresses of hosts on the network. The ethers file can be used in conjunction with or instead of other ethers sources, including the NIS maps ethers.byname and ethers.byaddr, or Ethernet address data stored on an LDAP server. Programs use the ethers(3C) routines to access this information.

The ethers file has one line for each host on an Ethernet. The line has the following format:

Ethernet-address official-host-name

Items are separated by any number of SPACE and/or TAB characters. A ‘#’ indicates the beginning of a comment extending to the end of line.

The standard form for Ethernet addresses is “x:x:x:x:x: x” where x is a hexadecimal number between 0 and ff, representing one byte. The address bytes are always in network order. Host names may contain any printable character other than SPACE, TAB, NEWLINE, or comment character.


Few systems other than boot servers have an ethers file. Most systems instead rely on arp(4P) to map between Ethernet addresses and IP addresses on their local network.



file listing Ethernet hosts

See Also

ethers(3C), arp(4P), hosts(5), nsswitch.conf(5)