Any programmer who’s ever been burned by data loss can tell you—you’ve got to have backups of your work. If it’s code, perhaps they use a version control system such as Subversion. If it’s something a little less-readily available, such as a weekly database text file dump, it might take a bit more work.
Here’s the scenario: I am using an external (and reliable) Subversion host for my code, and so I breathe easy for the most part knowing that it’s not under the umbrella of my shaky hosting provider. The MySQL databases involved in the project, however, live on the unstable system in question. Since switching providers is not presently feasible (which I will explain later), I decided I would take advantage of Linux’s powerful command-line scripting options and create a cronjob that would e-mail me a compressed tarball of the weekly mysqldump output. Simple enough, yeah?
Well… almost. I’ll get to that in a minute. Let’s start with the first piece of the finished product: the mysqldump command.
mysqldump -u<username> -p<password> --ignore-table=first_db.some_table --databases first_db second_db > backup.sql
Now, let’s break that command down piece by piece:
- mysqldump – This command is used to dump the structure and/or contents of one or more MySQL databases to the console (or, as we will be doing, through a command pipeline to a text file).
- -u<username> – This option designates the username to connect to the MySQL server with. In this case, I am using a meaningless placeholder. Replace it with your desired username.
- -p<password> – This option designates the password to connect to the MySQL server with. Keep in mind that this parameter will show up in proc for a short time, and other users on your system will be able to view it. You might consider an alternative method (or leverage a MySQL account with restricted privileges).
- –ignore-table=first_db.some_table – This option specifies a table that I would not like to include in the mysqldump results. Maybe it’s full of cruft, maybe it’s expendable—the point is, we don’t want it in there. To specify multiple tables to ignore, simply reuse the directive. “first_db” and “some_table” are just used as an example, but note that table names must be prefixed with their database name.
- –databases first_db second_db – This option specifies which database(s) we will be dumping the structure and/or contents of. The option flag is unnecessary if there is only one database and it is the last token in the command line. In this case, “first_db” and “second_db” are used as example database names.
The last bit of the command line uses the shell’s output redirection token (the greater-than symbol) to write the results of the mysqldump command to a file (“backup.sql” in the example).
Now that we’ve got our database dump in a text file, let’s compress it and e-mail it to ourselves, right?
Well… almost. Here’s where I ran into a tad bit of a snag. You see, compressed files—at least the one we’re about to create—are full of binary data (rather than textual data), and as such, tend to be mercilessly flogged during transfer through SMTP and the like. How can we represent the binary file as textual data in order to send it via email, you ask? The answer, my friends, is uuencode! First, though, let’s look at the snippet for compressing the mysqldump output.
tar cjf backup.tar.bz2 backup.sql otherfile.txt
So, what are we doing there?
- tar cjf – The tar command, or tape archive, is used to gather a list of files into one “tarball”—basically, an uncompressed archive. The “cjf” options we’re passing to the tar command signify three things:
- c – Create a new tarball with the file(s) specified.
- j – Compress the tarball using the bzip2 program.
- f – Specify which file(s) to roll together in the tarball.
- backup.tar.bz2 – This is our desired created archive name. This is what we will be emailing to ourselves in a moment.
- backup.sql otherfile.txt – These are the files used in our example which will be added to the “backup.tar.bz2” archive. I have included more than just the mysqldump output in order to illustrate the usefulness of tar in archiving multiple files for bzip2 to compress.
Now that we’ve created a (binary) compressed archive of the files we want to email, we’ll need to encode them as textual data by using the uuencode command. In this next snippet, we’ll be encoding the archive we just made and routing it through the mail command to email it to ourselves.
uuencode backup.tar.bz2 backup.tar.bz2 | mail [email protected] -s "weekly backup"
The reason for duplicating the archive name when invoking the uuencode command is that the first represents the local file name and the second represents the destination filename (for when the data is decoded on the receiving end). When we pipe the output of our uuencode operation through mail, most email clients will immediately recognize the encoded text as a file attachment and handle it appropriately.
We pass the mail command our destination address first, and then, using the -s flag, we provide the subject for the email message. If you like, you can even use a bit of fancy footwork to send through a message body separate from the attachment—but that’s for another post entirely.
So, we’ve stepped through each of the necessary processes in dumping, collecting, compressing, encoding, and emailing our database backup. When we string them all together into one text file like so, we have a quaint little package that can be tied into crontab for scheduling:
rm backup.tar.bz2 mysqldump -u<username> -p<password> \ --ignore-table=first_db.some_table \ --databases first_db second_db > backup.sql tar cfj backup.tar.bz2 backup.sql otherfile.txt rm backup.sql uuencode backup.tar.bz2 backup.tar.bz2 | mail [email protected] -s "weekly backup"
I’ve set up a very similar script to send me the database dump of my project (and its accompanying wiki) every Monday morning, and it’s working like a dream. Hopefully, you will be able to leverage this collection of simple command-line utilities to similarly-beneficial ends! (Note: The “rm” commands were added to clean up copies of the files from previous script runs. By default, bzip2 will not create the archive if the filename specified already exists.)