Foreword¶

From rsync Brief Description we know that rsync is an incremental synchronization tool. Every time the rsync command is executed, data can be synchronized once, but data cannot be synchronized in real time. How to do it?

With inotify-tools, this program tool can realize one-way real-time synchronization. Since it is real-time data synchronization, the prerequisite is to log in without password authentication.

Regardless of whether it is rsync protocol or SSH protocol, both can achieve password-free authentication login.

First, generate a public key and private key pair on the client, and keep pressing Enter after typing the command. The key pair is saved in the /root/.ssh/ directory.

[root@fedora ~]# ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa
Your public key has been saved in /root/.ssh/id_rsa.pub
The key fingerprint is:
SHA256: TDA3tWeRhQIqzTORLaqy18nKnQOFNDhoAsNqRLo1TMg root@fedora
The key's randomart image is:
+---[RSA 2048]----+
|O+. +o+o. .+. |
|BEo oo*....o. |
|*o+o..*.. ..o |
|.+..o. = o |
|o o S |
|. o |
| o +. |
|....=. |
| .o.o. |
+----[SHA256]-----+

Then, use the scp command to upload the public key file to the server. For example, I upload this public key to the user testrsync

[root@fedora ~]# scp -P 22 /root/.ssh/id_rsa.pub root@192.168.100.4:/home/testrsync/

[root@Rocky ~]# cat /home/testrsync/id_rsa.pub >> /home/testrsync/.ssh/authorized_keys

Try to log in without secret authentication, success!

[root@fedora ~]# ssh -p 22 testrsync@192.168.100.4
Last login: Tue Nov 2 21:42:44 2021 from 192.168.100.5
[testrsync@Rocky ~]$

tip

The server configuration file /etc/ssh/sshd_config should be opened PubkeyAuthentication yes

On the client side, the rsync service prepares an environment variable for the system-RSYNC_PASSWORD, which is empty by default, as shown below:

[root@fedora ~]# echo "$RSYNC_PASSWORD"

[root@fedora ~]#

If you want to achieve password-free authentication login, you only need to assign a value to this variable. The value assigned is the password previously set for the virtual user li. At the same time, declare this variable as a global variable.

[root@Rocky ~]# cat /etc/rsyncd_users.db
li:13579

[root@fedora ~]# export RSYNC_PASSWORD=13579

Try it, success! No new files appear here, so the list of transferred files is not displayed.

[root@fedora ~]# rsync -avz li@192.168.100.4::share /root/
receiving incremental file list
./

sent 30 bytes received 193 bytes 148.67 bytes/sec
total size is 883 speedup is 3.96

tip

You can write this variable into /etc/profile to make it take effect permanently. The content is: export RSYNC_PASSWORD=13579

Author: tianci li

Contributors: Steven Spencer, Ganna Zhyrnova

Foreword¶

SSH protocol password-free authentication login¶

rsync protocol password-free authentication login¶