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This article is to share with you about how to use Unison to achieve two-way file synchronization in Linux, the editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.

A brief introduction to Unison

Unison is a file synchronization tool that can be used on Windows, Linux, and other Unix platforms. It keeps the contents of two folders (local or online) consistent. Unison has the same features as some other synchronization tools or file systems, but also has its own characteristics:

1. Cross-platform use

two。 There are no special requirements for kernel and user permissions

3.Unison is bi-directional, it can automatically handle the parts of the two copies that are updated without conflicts, and the parts with conflicts will be displayed for the user to choose the update policy.

4. As long as the two hosts can be connected, you can run unison, you can directly use socket connection or secure ssh connection, do not require high bandwidth, and use a compressed transmission protocol similar to rsync.

The environment is as follows:

Vm1:10.13.114.19

Vm2:10.13.114.32

II. Compile and install Unison

Objective Caml compiler is required when installing Unison through source package compilation under Linux.

Install in the following ways

[root@vm1 ~] # wget http://caml.inria.fr/pub/distrib/ocaml-3.12/ocaml-3.12.1.tar.gz

[root@vm1 ~] # tar-xzvf ocaml-3.12.1.tar.gz

[root@vm1 ~] # cd ocaml-3.12.1

[root@vm1 ocaml-3.12.1] #. / configure

[root@vm1 ocaml-3.12.1] # make world opt

[root@vm1 ocaml-3.12.1] # make install

Compile and install Unison

[root@vm1 ~] # wget http://www.seas.upenn.edu/~bcpierce/unison//download/releases/stable/unison-2.40.63.tar.gz

[root@vm1 ~] # tar-xzvf unison-2.40.63.tar.gz

[root@vm1 ~] # cd unison-2.40.63

[root@vm1 unison-2.40.63] # make UISTYLE=text

[root@vm1 unison-2.40.63] # make install

During the execution of make install, the following error message may appear:

Mv: cannot stat'/ root/bin//unison': No such file or directory

Make: [doinstall] Error 1 (ignored)

Cp unison / root/bin/

Cp: cannot create regular file'/ root/bin/': Is a directory

Make: * * [doinstall] Error 1

The reason for the error is that Unison defaults to Copy files to the / root/bin directory, but Linux does not have this directory by default, so we need to copy the generated executable unison to the system's PATH directory.

[root@vm1 unison-2.40.63] # cp unison / usr/local/bin

Upload the executable file unison to the remote host 10.13.114.32

[root@vm1 unison-2.40.63] # scp unison root@10.13.114.32:/root/

Log in to the remote host through SSH, and copy the unison to the PATH directory of vm2

[root@vm2 ~] # cp unison / usr/local/bin

3. Configure ssh key trust

It is recommended to operate through ordinary users, on the grounds that the operation through root itself is dangerous, and the password-free login root is even more dangerous.

Create an admin user on both servers

[root@vm1] # useradd-m admin

[root@vm1 ~] # passwd 12345

[root@vm2] # useradd-m admin

[root@vm2 ~] # passwd 123456

Create key on vm1 and configure trust for vm2

[root@vm1 ~] # su-unison

[admin@vm1] $ssh-keygen-t rsa

Use default values when prompted to save the location of the private key (key) and the public key (public key)

When prompted whether a private key password (passphrase) is required, hit enter directly, that is, do not use the private key password.

After that, a pair of keys, id_rsa (private key file) and id_rsa.pub (public key file), are generated and saved in the / home/unison/.ssh/ directory.

Add the public key to the authorized_keys file of vm2

Upload files to vm2

[admin@vm1] $scp ~ / .ssh/id_rsa.pub unison@10.13.114.32:/home/unison/

Use the rsync user SSH to log in to the remote host and add the public key to the authorized_keys file

[admin@vm2 ~] $mkdir .ssh

[admin@vm2 ~] $chmod 700.ssh

[admin@vm2] $mv ~ / id_rsa.pub ~ / .ssh/authorized_keys

[admin@vm2] $chmod 600 ~ / .ssh/authorized_keys

Similarly, perform the following steps to create a key on vm2 and configure trust for vm1

[root@vm2 ~] # su-admin

[admin@vm2] $ssh-keygen-t rsa

Upload files to vm1

[admin@vm2] $scp ~ / .ssh/id_rsa.pub unison@10.13.114.19:/home/unison/

Use the rsync user SSH to log in to vm1 and add the public key to the authorized_keys file

[admin@vm1] $mv ~ / id_rsa.pub ~ / .ssh/authorized_keys

Restart the SSH service

[root@vm1 ~] # / etc/init.d/sshd restart

[root@vm2 ~] # / etc/init.d/sshd restart

IV. Configuration and use of Unison

Create a test directory on both servers for testing

[root@vm1 ~] # su-admin

[unison@vm1 ~] $mkdir test

[root@vm2 ~] # su-unison

[unison@vm2 ~] $mkdir test

Execute unison once on both servers, and if prompted for confirmation, hit enter directly to select the default value.

[unison@vm1 ~] $unison / home/admin/test/ ssh://admin@10.13.114.32//home/admin/test/

[unison@vm2 ~] $unison / home/admin/test/ ssh://admin@10.13.114.19//home/admin/test/

Modify the unison configuration files for both servers and enter the following

[unison@vm1 ~] $vim / home/unison/.unison/default.prf

# Unison preferences file root = / home/admin/test root = ssh://admin@10.13.114.32//home/admin/test/ # force = # ignore = batch = true # repeat = 1 # retry = 3 owner = true group = true perms =-1 fastcheck = false rsync = false sshargs =-C xferbycopying = true log = true logfile = / home/unison/.unison/unison.log

[unison@vm2 ~] $vim / home/unison/.unison/default.prf

# Unison preferences file root = / home/admin/test root = ssh://admin@10.13.114.19//home/admin/test/ # force = # ignore = batch = true # repeat = 1 # retry = 3 owner = true group = true perms =-1 fastcheck = false rsync = false sshargs =-C xferbycopying = true log = true logfile = / home/unison/.unison/unison.log

The relevant notes are as follows:

Force indicates that the directory will be synchronized to the remote end based on the folder specified locally. Note here that if the force parameter is specified, the Unison becomes a single synchronization, that is, it will be synchronized based on the folder specified by force, similar to rsync.

The basic principle of Unison two-way synchronization is: if there are two AB folders, A folder synchronizes its own changes to the BUnison B folder and synchronizes its own changes to A. finally, the contents of the two AB folders are the same, which is a collection of AB folders.

One disadvantage of Unison two-way synchronization is that unison does not synchronize when a file is modified in both synchronized folders, because unison cannot determine which one shall prevail.

Ignore = Path means that the specified directory is ignored, that is, it is not synchronized when synchronizing.

Batch = true, which indicates full automatic mode, accepts the default action, and executes it.

-fastcheck true means that the synchronization is compared only by the creation time of the file. If the option is false,Unison, the contents of the files in the two places will be compared.

Log = true indicates that the operation information is output at the terminal.

Logfile specifies the output log file.

In addition, Unison has many parameters, here are only a few commonly used, please refer to the Unison manual for details.

-auto / / accepts the default action and waits for the user to confirm whether to execute it.

-batch / / batch mode, fully automatic mode, accepts default actions and executes.

-ignore xxx / / add xxx to the ignore list

-ignorecase [true | false | default] / / whether to ignore file name case

-follow xxx / / whether synchronization of symbolic links pointing to content is supported

Owner = true / / keep the owner of the synchronized file

Group = true / / keep synchronized filegroup information

Perms =-1 / / keep the read and write permissions of synchronized files

Repeat = 1 / / start a new synchronization check after an interval of 1 second

Retry = 3 / / failed retry

Sshargs =-C / / compressed transmission using ssh

Xferbycopying = true "

-immutable xxx / / unchanged directory, which can be ignored when scanning

-silent / / quiet mode

-times / / synchronous modification time

The-path xxx parameter / / synchronizes only the subdirectories and files specified by the-path parameter, not the entire directory.-path can occur multiple times.

The unison configuration file under PS:Windows is located in the C:\ Documents and Settings\ currentuser\ .unison directory by default, and the default configuration file name is default.prf.

5. Testing

First create a file or directory under the / home/unison/test directory of server1 and server2, then execute unison on server1, and then if you can see the created files on both server1 and server2, the synchronization is successful.

Create files on server1 and server2, respectively

[unison@server1 ~] $cd test

[unison@server1 test] $touch 1.txt touch 3.txt

[unison@server2 ~] $cd test

[unison@server2 test] $touch 2.txt touch 4.txt

Execute unison on server1

[unison@server1 ~] $unison

Check whether files are synchronized on server1 and server2

[unison@server1 ~] $cd test

[unison@server1 test] $ls

1.txt 2.txt 3.txt 4.txt

[unison@server2 ~] $cd test

[unison@server2 test] $ls

1.txt 2.txt 3.txt 4.txt

All the "1.txt 2.txt 3.txt 4.txt" files have been seen, indicating that the file synchronization has been successful!

Note: you may need to enter a password the first time you connect to SSH, but then you don't need to enter it.

VI. Perform synchronization regularly or in real time

If you want to execute on a regular basis, do so through crontab scheduled tasks, for example, by setting up execution every 5 minutes in the following ways

[root@server1 ~] # su-unison

[unison@server1] $crontab-e

1 * / 5 * / usr/local/bin/unison

The above is how to use Unison to achieve two-way file synchronization in Linux. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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