How easy is it, to write a program that removes a file or a folder? Okay, assume you have all the power a modern operating system provides you, including rm shell convenience command, and unlink system call. Do you really think the answer is still "very"?.. Then take a look at these examples.

### Permission trap

Today one of my peers, Denis, was writing a program that somehow analyzed packages in Mandriva Linux distribution. Since trying to analyze the contents of a package without unpacking it looks more like gynecologist's work than that of a programmer, the software Denis wrote unpacked it first. Then it analyzed the package, and erased it with rm -rf in order to avoid disk pollution.

But sometimes it failed to erase it, which led to strange failures of the whole program.

The reason was the permission trap. Common sense tells us that if you can create a file, then you can remove it. This is wrong when it comes to uncommon permissions. Certain software that is very secure sets up specific attributes for certain files. In particular, it revoked writing permissions from certain catalogs, which prevented recursive removal of the unpacked files. You may try it yourself:

### ***

Usually, you think that creating is easy, and destroying is simple. In many cases, however, it's not true. In Russia, for instance, it's much easier to open a business than to shut it. And when it gets to removing files, it's also sometimes true. So, if your program really depends on successful file removing, it should be more careful with such a seemingly simple operation.

# Comments imported from the old website

Maxim Ivanov on 21 November 2011 commented:

In case of abusive logging, I found handy to run ">/path/to/logfile", which effectively frees up space.

Pavel Shved on 17 December 2011 commented:

@Maxim, this sometimes works, and sometimes does not. I'm yet to figure out the exact conditions one may rely on this under.