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Working with scen

Existing server An and server B synchronize these changes to the target directory of server B in real time if the content in the specified directory of server A (for example, / home/paul/rsync/) changes (add, delete and attribute changes).

Data mirroring backup tool Rsync

Rsync is a very fast and flexible file copy tool. It supports file replication either locally or between remote servers. Rsync uses the delta-transfer algorithm, which only needs to transmit the file differences between the source side and the destination side, which greatly reduces the network bandwidth consumption and replication time. Rsync is mostly used for data backup and mirroring.

Rsync uses a quick check algorithm to determine whether a file needs to be synchronized by comparing changes in file size or last modification time.

There are two ways for Rsync to connect to remote hosts: using ssh or rsync daemon. Here, Rsync is used to back up remote files.

Installation and operation of Rsync

Install Rsync

Execute on the terminal of server An and server B, respectively:

Sudo yum install rsync

After installation, you will find that the configuration file for rsync is located in etc/rsyncd.conf. This file needs to be used when synchronizing with daemon, which is not described here.

Configure secret-free login between servers An and B

Server An executes:

IP address of ssh-keygenssh-copy-id server B

Create source-side and destination-side directories

In Server A:

Mkdir / home/paul/rsync

In Server B:

Mkdir / home/paul/rsync

Create a test file on server A

Echo "Hello from Server A" > > / home/paul/rsync/demo.txt

Execute file transfer command

Run on server A:

# (1) rsync-avPz-progress / home/paul/rsync 192.168.100.130:/home.paul/rsync# (2) rsync-avPz-delete-progress / home/paul/rsync 192.168.100.130:/home.paul/rsync

You will find that demo.txt also appears in the / home/paul/rsync directory on server B.

Command parsing:

(1) copy the files in the / home/paul/rsync directory in server A to the / home.paul/rsync in server B (192.168.100.130).

(2) compare the files on the destination side and the source side, and delete the file on the destination side if the file on the destination side does not exist on the source side.

Problems in Rsync

Rsync is only a file copy tool, and it cannot monitor the addition, deletion and modification of files on the source side. After making changes on the source side, you need to execute the rsync command to synchronize the changes to the target side.

Rsync needs to scan the entire directory before each synchronization. If there are a large number of files in the source directory, the scan may take more time.

In order to meet the requirements of real-time monitoring, we need to introduce another tool: inotify.

File system event listener inotify

Inotify-tools provides a simple interface for inotify. It is a library written in c language and also contains command-line tools.

For a detailed introduction of inotify-tools, please click: https://github.com/rvoicilas/inotify-tools/wiki

Installation of inotify-tools

For centos7 systems, execute the following sequence:

Yum install-y epel-releaseyum-- enablerepo=epel install inotify-tools

Use the inotifywait command to listen for events

The listening script is as follows (inotifywait-rsync.sh):

Inotifywait-mrq-- timefmt'% d/%m/%y% HGV% M'-- format'% T% w% f'-e modify,delete,create,attrib / home/paul/rsync/ | while read filedorsync-avPz-- progress / home/paul/rsync/ 192.168.100.130:/home/paul/rsync/rsync-avPz-- delete / home/paul/rsync/ 192.168.100.130:/home/paul/rsync/echo "${file} was synchronized" done

Parameter analysis

-m remains in a continuous listening state. If this parameter is not written, inotifywait will exit after listening to an event. -r listens to directories recursively. -Q quiet mode, print out less content. -timefmt specifies the output format of the time. -- format specifies the format of the event output. -e sets the type of event to listen for. Here we listen for additions, deletions and metadata changes.

For each listening time triggered, inotifywait executes the code between do and done. Here, we invoke the rsync command mentioned earlier for file synchronization.

Listen to the script and join crontab

Crontab-e * sh / home/paul/inotifywait-rsync.sh

references

Https://rsync.samba.org

Https://github.com/rvoicilas/inotify-tools/wiki

The above is the whole content of this article, I hope it will be helpful to your study, and I also hope that you will support it.

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