Defining the Linux hostname in/etc/hosts

The problem today is that a program is always 0x7f000001 when it gets an IP address on a newly installed Linux server. At first no attention, then carefully think, 0x7f000001 not just is 127.0.0.1 well. A colleague looked up the/etc/hosts and found a line in the file:

127.0.0.1 mylinuxsvr localhost.localhost.localdomain localhost

Among them, Mylinuxsvr is the name of this server. No wonder you can only get 127.0.0.1 every time. Of course, this server's IP address is actually good, but somehow, there is a different server communication between the program to get the IP address through/etc/hosts ...

Found some articles on Linux server network configuration, recorded here: Quick HOWTO:Ch03:Linux networking adding Red Hat Enterprise Linux Hosts

The following abstracts are from Quick HOWTO:Ch03:Linux networking.

Configuring Your/etc/hosts File

The/etc/hosts file is just a list of IP addresses and their corresponding server names. Your server would typically check this file before referencing DNS. If the name is found with a corresponding IP address then DNS won ' t being queried at all. Unfortunately, if the IP address is for this host changes, you are also have to also update the file. This May is a concern for a single server and but can become laborious if it has to being done companywide. For ease of management, it's often easiest to limit entries in this file to just the loopback interface and also the Serv Er ' s own hostname, and use a centralized DNS server to handle most of the rest. Sometimes you might is the one managing the DNS server, and in such cases it may is easier to add a quick/etc/hosts f Ile entry till the centralized change can be made.

192.168.1.101  Smallfry

In the example above server Smallfry has a IP address of 192.168.1.101. You can access 192.168.1.101 using the ping, Telnet or no other network aware is referring to it as Smallfry. This is a example using the ping command to-whether Smallfry is alive and the network:

[Root@bigboy tmp]# ping smallfry
Ping Zero (192.168.1.101) bytes of data.
Bytes from Smallfry (192.168.1.101): icmp_seq=0 ttl=64 time=0.197 ms-bytes from
smallfry (192.168.1.101): icmp_s  Eq=1 ttl=64 time=0.047 ms


---smallfry ping statistics---
2 packets transmitted, 2 received, 0% packet loss, time 2017ms
RTT Min/avg/max/mdev = 0.034/0.092/0.197/0.074 ms, pipe 2
[Root@bigboy tmp]#

You can also add aliases to the "end of the" which enable you to refer to the server using other names. Here we are have set it up so this smallfry can also be accessed using the names Tiny and Littleguy.

192.168.1.101  smallfry  Tiny  Littleguy

You should never have a IP address more than once in this file because Linux would use only the values in the It finds.

192.168.1.101  Smallfry    # (wrong)
192.168.1.101  Tiny        # (wrong)
192.168.1.101  Littleguy   # (wrong)

The loopback Interface ' s localhost Entry

Usually the entry in/etc/hosts defines the IP address of the server ' s virtual Loopback interface. This is usually mapped to the name Localhost.localdomain (the universal name used when a server refers to itself) and Loca Lhost (the shortened alias name). By default, Fedora inserts the hostname of the server between the 127.0.0.1 and the localhost as this:

127.0.0.1     bigboy    localhost.localdomain    localhost

When the ' server is ' connected to the ' Internet this ' entry ' 127.0.0.1 needs to be the fully qualified domain n Ame (FQDN) of the server. For example, bigboy.mysite.com, like this:

127.0.0.1     bigboy.my-site.com    localhost.localdomain    localhost

Some programs such as Sendmail are very sensitive to-this and if they detect what they feel are an incorrect FQDN they would Default to using the ' name Localhost.localdomain when communicating with another server ' on the network. This can cause confusion, as the other server also feels it is localhost.localdomain.

Note:you must always have a localhost and localhost.localdomain entry mapping to 127.0.0.1 for Linux to work properly and Securely.