


What to do if modifying the hosts file in Linux is invalid
#What should I do if modifying the hosts file in Linux fails?
1. Linux often fails to take effect after modifying the hostName of the local alias /etc/hosts. Solution
Linux modifies the hostName of the local alias /etc/hosts It often does not take effect.
For example, the content of our /etc/hosts is as follows:
#192.68.1.10 message.xxx.com 192.68.1.11 message.xxx.com
But ping message.xxx.com still points to 192.68.1.10.
Related recommendations: "linux tutorial"
## Generally there are 2 solutions:
1). Restart, this is the most direct, reliable and stable method. If it is sometimes inconvenient to restart, you can use the second method. 2). Modify the /etc/sysconfig/network file and change HOSTNAME to the corresponding alias, as follows:NETWORKING=yes HOSTNAME=host1Restart the network service after modification
service network restart (本质是/etc/init.d/network)3). If it still doesn't work after restarting the server, it may be caused by the local DNS cache. Check whether nscd is enabled: ps -ef|grep nscd Directly turn off the Linux nscd cache service:
/etc/init.d/nscd stop
2. Linux DNS
Linux itself does not have dns cache. If you want to use dns cache, you need to install a service program NSCD (name service cache daemon). nscd caches three services passwd group hosts, so it will record Three libraries correspond to the sources /etc/passwd, /etc/hosts and /etc/resolv.conf. Each library saves two caches, one for records found and one for records not found. Each cache saves a time to live (TTL). Installation:yum install nscdModify the configuration file /etc/nscd.conf, enable dns caching, and modify this line
enable-cache hosts yesIf the nscd service is enabled, there will be dns cache, otherwise there will be no dns cache. Start, stop, and restart the service
service nscd start | stop | restartnscd configuration: You can enable the local DNS cache by editing the /etc/nscd.conf file and adding the following line: enable-cache hosts yesThe configuration on the Alibaba Cloud host is as follows:
[root@iZ2571ykq ~]# cat /etc/nscd.conf #logfile /var/log/nscd.log threads 6 max-threads 128 server-user nscd debug-level 5 paranoia no enable-cache passwd no enable-cache group no enable-cache hosts yes positive-time-to-live hosts 5 negative-time-to-live hosts 20 suggested-size hosts 211 check-files hosts yes persistent hosts yes shared hosts yes max-db-size hosts 33554432The explanation of relevant parameters is as follows: logfile debug-file-name : Specify the file name to which debugging information is written. debug-level value: Set the desired debugging level. threads number: This is the number of threads started waiting for requests. A minimum of 5 threads will be created. server-user user: If this option is set, nscd will run as this user, not as root. If each user uses a separate cache (-S parameter), this option will be ignored enable-cache service
nscd -g 查看统计信息Clear the nscd cache:
nscd -i passwd nscd -i group nscd -i hostsOf course, delete the cache library or stop the nscd service first:
rm -f /var/db/nscd/hosts service nscd restartOr directly stop the nscd service service nscd stop.
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