Stupid afio Tricks

I've already covered tar and all the wonderful ways to use it, but it's not the only tool at your disposal. Another popular backup tool is afio. Depending on your distribution, it already may be installed. On Ubuntu, for example, run the following to install it:

sudo apt-get install afio

Now you have a fairly powerful tool at your disposal for archiving files and making backups.

By default, afio reads and writes the files being archived on standard input and standard output. This means you can create a list of files to archive with another program, like find, and pipe it to afio to do the actual archive. Once you have your list of files, you can apply five basic commands to those files:

• -o — create an archive.
• -i — install (or unpack) an archive.
• -t — test (or list) the files stored in an archive.
• -r — verify the files stored in an archive against the filesystem.
• -p — copy the files to a given directory location.

If you want to create a simple archive of all of your C source code files, execute:

find . -name *.c -print | afio -o -Z source_code

When you want to extract these files again, execute:

afio -i -Z source_code

When you run afio as a regular user, all file paths are stored with no leading /. This means when you unpack an archive, it unpacks in the current directory. The idea is to avoid overwriting system files accidentally. To keep the leading /, use the command-line option -x. Running afio as the superuser reverses this behavior—any leading / is maintained, and you need to use the command-line option -X to get the usual behavior of stripping the leading /.

If space is at a premium, afio also can compress your archive, just like tar, with the -Z command-line option. There is one very big difference, however. When you compress a tar archive, the entire archive file is compressed. This means if one part of the file is corrupted, you potentially could lose all the files in the archive. When you compress an afio archive, the archived files actually are compressed individually. So if one file becomes corrupted, by whatever means, you won't lose any of the other files in the archive.

When you compress an archive, afio uses gzip by default. You can tell gzip what compression factor to use with the -G num command-line option, where num is the amount of compression gzip will apply to the archived files. This is a number between 0 (for no compression) and 9 (for maximum compression), with a default of 6.

You may need to balance how much CPU and how much IO time is being used during the compression phase. If so, you can limit when compression is to be used. The command-line option -T threshold tells afio not to try compressing a file unless it is at least threshold bytes in size. The default setting is -T 0k, so afio tries to compress all files, no matter how small. At the other end of the spectrum, you may want to limit how large a file can be before afio tries to compress it. You can do that with the command-line option -2 max, where max is the maximum file size. The default in this case is -2 200m, so afio won't try to compress files larger than 200MB.

What if you don't want to use gzip as your compression method? You can change this by using the command-line option -P progname, where progname is the name of the executable to use to do the compression.

If you need to hand options in to this alternate program, use the -Q opt option. You need to use separate -Q options for each option you want to hand in to the alternate program. Because afio simply executes this alternate program, you can run anything at this stage, such as an encryption program, allowing you to encrypt your archive. To encrypt your archive using PGP, execute:

export PGPPASSFD=3
find . -name *.c -print | afio -ovz -Z -U -P 
 ↪pgp -Q -fc -Q +verbose=0 -3 3 archive 3

This runs PGP on all files in the archive as they are added.
The last afio trick is having the ability to interact with archives on external systems in a similar manner as you would with tar. The format looks like this:
[user@]host[%rsh][=afio]:file

The option user@ is the user name you would use to access the external system. The default communications mechanism is rsh, but you can change that to ssh with the option %ssh. You can define the command to use on the external system with the option =afio. You can use this if the executable is named something else or in an odd location. So, if you want to archive all your source code files onto an external server over ssh, you could execute:
find . -name *.c -print | afio -o -Z user@server%ssh:archive

Using afio, go forth and ensure that you have proper backups of all of your important information.