Using Netcat for Backup

From RSWiki
Revision as of 14:04, 8 December 2009 by Robert (talk | contribs)
Jump to navigation Jump to search


Please considering making a donation to keep this site running In the three years that I have been running this site costs have increased significantly. Unfortunately advertising does not come anywhere near covering the costs to keep this site running. Any donations, however small will help enormously in keeping this site running. If you found the information on this page helpful in any way why not make a donation now? <donationform></donationform>

Getting started

Providing you have netcat installed, on the destination machine execute the following command:

nc -l -p 6666 > filename.tar.bz2

This creates a listening socket on port 6666 with the filename specified above.

We now need to setup the source machine to dump whatever directories or filesystems you want to send to the destination machine.

So on the source you can issue the following command:

tar jlcvPpf - / > /dev/tcp/

In the example above is the address of the destination address and the forward slash indicates that it is the entire filesystem to be backed up. You can easily change this for example to tar jlcvPpf - /var/www > /dev/tcp/ to backup the /var/www directory.

If there is no /dev/tcp it is possible to use netcat on both ends

tar jlcPpf - / | nc 6666

The options for the tar command are as follows:

  • j - do bzip2 compression on the archive
  • l - one file system
  • c - create archive
  • v - be verbose about it
  • P - don't strip leading / from pathnames
  • p - preserve permissions
  • f - the file name to write, which in this case is - which means standard output.

Sending back the compressed archive

There is no need to send the whole archive back to the client, and then decompress it. This can all be done at once

  • On host machine
nc -l -p 6666 < foo.tar.bz2

  • On client machine
nc 6666 | tar -xj

If the client is a very slow machine it might be faster to decompress on the host


bzip2 -d --stdout foo.tar.bz2 | nc -l -p 6666


nc 6666 | tar -x

Some Updates

Below is some information added by Colm Buckley on the Irish Linux Users Group mailing list.

If you have more than one directory to be transferred, you can list several on the "tar" command line above, or even use a wildcard - although if there are very many, the wildcard might expand to more than the capacity of the command line. Experimentation will reveal the best thing to do.

On the server, do:

nc -l -p 6666 | tar xvf -

That tells it to listen on the socket and pipe the results directly into the tar expand command.