How to take effect after/etc/hosts file modification

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After modifying the/etc/hosts, the normal situation should be effective immediately after the save, but sometimes not. use uname-a to see how hostname is, and you can see if the changes are in effect. if not
the policy at this time is:
1) Restart the Machine
2) Restart service
     Ubuntu:  $sudo /etc/init.d/ Networking Restart       gentoo: /etc/init.d/net.eth0restart 3) using hostname command        hostname defined host name
hostname relationship to/etc/hosts

Many people mention change hostname first of all think about modifying/etc /hosts file, think the hostname configuration file is/etc/hosts. Actually, it's not. The

Hosts file functions as DNS, providing a corresponding IP address to hostname. Early Internet computers were few, and the stand-alone hosts file was sufficient to store all networked computers. But with the development of the Internet, this is far from enough. The distributed DNS system is then present. By the DNS server to provide a similar IP address to the domain name of the corresponding. Concrete can be manhosts. The

Linux system queries the/etc/hosts file before it sends a domain resolution request to the DNS server, and if it has a corresponding record, it uses the records in the hosts. /etc/hosts files typically contain this record

127.0.0.1   localhost.localdomain  localhost The
Hosts file format is one line of records, the IP address hostname aliases, the three separated by white space characters, and the aliases optional .

127.0.0.1 to localhost this recommendation is not to be modified because many applications use this, such as SendMail, which may not function properly after modification.