Wednesday, March 11, 2009

rsync - synchronizing two file trees

rsync - synchronizing two file trees 15 December 2000
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This article originally appeared quite some time ago. But for some unknown reason, it was lost from the indexes. I've just come back to upgrade it with some new error observations.
We now return you to your regularly scheduled read...

rsync is an amazing and powerful tool for moving files around. I know of people that use it for file transfers, keeping dns server records up-to-date, and along with sshd to remote restart the services when rsync reports a file change (how they do that, I don't know, I'm just told they do it).

This article describes how you can use rsync to synchronize file trees. In this case, I'm using two websites to make sure one is a backup of the other. As an example, I'll be making sure that one box contains the same files as the other box in case I need to put the backup box into production, should a failure occur.

rsync can be used in six different ways, as documented in man rsync:

for copying local files. This is invoked when neither source nor destination path contains a : separator
for copying from the local machine to a remote machine using a remote shell program as the transport (such as rsh or ssh). This is invoked when the destination path contains a single : separator.
for copying from a remote machine to the local machine using a remote shell program. This is invoked when the source contains a : separator.
for copying from a remote rsync server to the local machine. This is invoked when the source path contains a :: separator or a rsync:// URL.
for copying from the local machine to a remote rsync server. This is invoked when the destination path contains a :: separator.
for listing files on a remote machine. This is done the same way as rsync transfers except that you leave off the local destination.
I'll only be looking at copying from a remote rsync server (4) to a local machine and when using a remote shell program (2).

This was an easy port to install (aren't they all, for the most part?). Remember, I have the entire ports tree, so I did this:
# cd /usr/ports/net/rsync
# make install

If you don't have the ports tree installed, you have a bit more work to do.... As far as I know, you need rsync installed on both client and server, although you do not need to be running rsyncd unless you are connecting via method 4.

Setting up the server
In this example, we're going to be using a remote rsync server (4). On the production web server, I created the /usr/local/etc/rsyncd.conf file. The contents is based on man rsyncd.conf.
uid = rsync
gid = rsync
use chroot = no
max connections = 4
syslog facility = local5
pid file = /var/run/

path = /usr/local/websites/
comment = all of the websites
You'll note that I'm running rsync as rsync:rsync. I added lines to vipw and /etc/group to reflect the new user. Something like this:

rsync:*:4002:4002::0:0:rsync daemon:/nonexistent:/sbin/nologin

Then I started the rsync daemon and verified it was running by doing this:

# rsync --daemon
# ps auwx | grep rsync
root 30114 0.0 3.7 936 500 ?? Ss 7:10PM 0:00.04 rsync --daemon
And I found this in /var/log/messages:

rsyncd[30114]: rsyncd version 2.3.2 starting
Then I verified that I could connect to the daemon by doing this:

# telnet localhost 873
Connected to localhost.
Escape character is '^]'.
I determined the port 873 by looking at man rsyncd.conf.

See the security section for more information.

You can also specify a login and user id. But if you do that, I suggest you make /usr/local/etc/rsyncd.conf non-world readable:

chmod 640 /usr/local/etc/rsyncd.conf
This example is straight from the man page. Add this to the configuration file:

auth users = tridge, susan
secrets file = /usr/local/etc/rsyncd.secrets
The /usr/local/etc/rsyncd.secrets file would look something like this:

And don't forget to hide that file from the world as well:

chmod 640 /usr/local/etc/rsyncd.secrets

Setting up the client
You may have to install rsync on the client as well.. There wasn't much to set up on the client. I merely issued the following command. The rsync server in question is ducky.
rsync -avz ducky::www /home/dan/test
In the above example, I'm connecting to ducky, getting the www collection, and putting it all in /home/dan/test.

And rsync took off! Note that I have not implemented any security here at all. See the security section for that.

I checked the output of my first rsync and decided I didn't want everything transferred. So I modified the command to this:

rsync -avz --exclude* --exclude wusage/* ducky::www /home/dan/test
See the man pages for more exclusion options.

I also wanted deleted server files to be deleted on the client. So I did this:

rsync -avz --delete ducky::www /home/dan/test
Of course, you can combine all of these arguments to suit your needs.

I found the --stats option interesting:

Number of files: 2707
Number of files transferred: 0
Total file size: 16022403 bytes
Total transferred file size: 0 bytes
Literal data: 0 bytes
Matched data: 0 bytes
File list size: 44388
Total bytes written: 132
Total bytes read: 44465

My transfers are occur on a trusted network and I'm not worried about the contents of the transfer being observed. However, you can use ssh as the transfer medium by using the following command:
rsync -e ssh -avz ducky:www test
Note that this differs from the previous example in that you have only one : (colon) not two as in the previous example. See man rsync for details. In this example, we will be grabbing the contents of ~/www from host ducky using our existing user login. The contents of the remote directory will be synchronized with the local directory test.

Now if you try an rsync, you'll see this:

$ rsync -e ssh -avz --delete ducky:www /home/dan/test
@ERROR: auth failed on module www
Here I supplied the wrong password and I didn't specify the user ID. I suspect it used my login. A check of the man page confirmed this. This was my next attempt. You can see that I added the user name before the host, ducky..

$ rsync -e ssh -avz --delete susan@ducky:www /home/dan/test
receiving file list ... done
wrote 132 bytes read 44465 bytes 1982.09 bytes/sec
total size is 16022403 speedup is 359.27
In this case, nothing was transferred as I'd already done several successful rsyncs.

The next section deals with how to use a password in batch mode.

Do it on a regular basis
There's no sense in having an rsync set up if you aren't going to use it on a regular basis. In order to use rsync from a cron job, you should supply the password in a non-world readable file. I put my password in /home/dan/test/rsync.password. Remember to chmod 640 that password file!
I put the command into a script file (, which looks like this:

/usr/local/bin/rsync -e ssh -avz --stats --delete susan@ducky::www /home/dan/test --password-file /home/dan/test/rsync.password
Remember to chmod 740 the script file!

Then I put this into /etc/crontab in order to run this command every hour (this should be all on one line):

7 * * * * root /usr/home/dan/ 2>&1 | mail -s "rsync script" root
The above will mail you a copy of the output.

If you want to use ssh as your transport medium, I suggest using using the authorized_keys feature.

My comments
I think rsync is one of the most powerful tools I've seen for transferring files around a network and the Internet. It is just so powerful! Although I actually use cvsup to publish the Diary, I am still impressed with rsync.

Some recent errors I encountered
I was recently adding some new files to my rsync tree. I found these errors:
receiving file list ... opendir(log): Permission denied
opendir(fptest): Permission denied
opendir( Permission denied
opendir( Permission denied
readlink dan: Permission denied
opendir(default): Permission denied
It took me a while to understand the problem. It's a read issue. rsyncd didn't have permission to read the files in question. You can either make rsynd run as a different user, or change the permissions on the files.

If you get the user id for rsync wrong, you'll see this error:

$ rsync -avz xeon::www /home/dan/rsynctest
@ERROR: invalid uid
I had the rsync user misspelt as rysnc.

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