Monthly Archives: March 2013

Moving large files? Try split first.

I often need to move large files between servers, usually between different data centers. If I have a 100 gig file that I need to move (SQL backups for example) it can take a VERY long time to try and transfer the data via FTP (RSYNC is not an option in this example).

I find that moving a file via FTP might transfer at 250k per second. But it is possible to transfer multiple files via FTP at the same time, all at 250k per second (seems strange right?).

To increase the speed of the transfer use the split command on unix to split the 100 gig file into pieces, transfer the pieces to the destination and then rebuild the pieces into the original file. Here is an example:

split -–bytes=500m database.sql.gz database_

This will split a large file into 500 meg pieces. The file being processed is database.sql.gz and it will result in pieces like database_aa, database_ab … etc.

Then using FTP, transfer the collection of files and have the process completed much faster vs. transferring a single large file.

Once you have all the files moved to the destination, you need to take all the pieces and put them back together. To do this, use cat.

cat database_* > database.sql.gz

If you are looking to combine the files back into one under Windows, from the command prompt try something like this:

copy /b database_* database.sql.gz

That’s it, I now have my original file restored and ready for processing.

DirectAdmin – Root Email Messages

When you setup DirectAdmin, notification messages are by default sent to  For most people this would not be practical.

To easily modify where all messages to root are sent, the easiest is to create a .forward file for the root user.

Execute the following command and messages to will automatically be forwarded to your actual email address and hey, you might actually get them that way.

echo "" > /root/.forward

In addition to that, you need to ensure the permissions are correct on the .forward file. If you are running Exim, it is really picky about the security level on the files by default.

I found this works:

chmod 0600 .forward

Compiling DNSDB into Exim on Debian/Directadmin

Directadmin by default uses Exim, however the DNSDB lookup module is not available. DNSDB allows Exim to perform DNS lookups as part of mail processing. I am using it to lookup SPF records of incoming mail.

Currently there is no way to add it, or enable it – not even using custombuild.  If you want it you must compile Exim from source.  Here is the procedure I used on a Debian box to get it activated.

First, ensure you have the dependencies for exim.

apt-get install libdb4.8-dev libperl-dev libsasl2-dev

Change all occurrences of 4.80.1 to the version you want to use.

tar xvzf exim-4.80.1.tar.gz
cd exim-4.80.1/Local
perl -pi -e 's/^EXTRALIBS/#EXTRALIBS/' Makefile
perl -pi -e 's/HAVE_ICONV=yes/HAVE_ICONV=no/' Makefile
perl -pi -e 's/^#LOOKUP_DNSDB=yes/LOOKUP_DNSDB=yes/' Makefile
cd ..
make install

The above commands will download the unmodified source for exim, extract it, download a makefile from the directadmin servers, use a perl command to adjust the makefile, compile and install the fresh exim build.

The file that is created is /usr/sbin/exim-4.80.1-1, so we must change the name and overwrite the existing exim file.

/etc/init.d/exim stop
cp -f /usr/sbin/exim-4.80.1-1 /usr/sbin/exim
chmod 4755 /usr/sbin/exim
/etc/init.d/exim start

To verify you have a working Exim with DNSDB compiled in do the following:

exim -bV

You should get an output from Exim, look for the line that lists the built-in lookups and confirm that dnsdb is listed (as seen in the image below).