Category Archives: Uncategorized

/etc/mtab weirdness

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There are many ways to fetch the list of currently-mounted-devices: read the files /etc/mtab, /proc/mounts, or exec /bin/mount, /bin/df.

I've been arguing with a colleague (Yaniv), that relying on /etc/mtab is no much worse than relying on /proc/mounts. But after we inspected it on Linux & Solaris (/etc/mnttab), I figured out that I was pretty wrong, and learned some new surprising facts:

On Linux:

  • /proc/mounts is a read-only, kernel-generated file.
  • /etc/mtab (Linux) is a regular file. It's kept up-to-date because the mount/umount commands modify it. It can be modified by a root user, moved and even deleted!
  • df command is using /etc/mtab, thus after rm'ing /etc/mtab, df would stop functioning.
  • mount command doesn't care about /etc/mtab, probably uses /proc/mounts or some internal kernel structure.

On Solaris (prepare for some weird stuff now):

  • Solaris has got /etc/mnttab, but no /proc/mounts equivalent.
  • /etc/mnttab is a mounted filesystem, of the mntfs type. So it's somewhat similar to /proc/mounts on Linux. It cannot be modified.
  • /etc/mnttab is actually a directory! (a mount point has to be a directory..)
  • /etc/mnttab can be unmounted, renamed, rmdir'd (when unmounted) and mounted anywhere else.
  • both df and mount rely on /etc/mnttab, thus not functioning when it's absent

On HP-UX:

  • /etc/mnttab, which is a regular file, is similar to /etc/mtab on Linux.

And on another, non-related subject: looks like Debian Lenny has got only 80 bugs to go (as of 19/01/09)! Go Lenny!

Israeli-web critique project

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Hi,

I've been writing about it two months ago, and at last I did it: a new blog (hebrew only) aiming at making the big Israeli web sites better (from technical point of view), by posting positive critics about current websites.

I invite you to:

  • Subscribe by RSS, to get the updates (and write talkbacks! 🙂 )
  • Give ideas for new articles (webwatchisrael at gmail.com)
  • Write new articles yourselves and send us (according to the guidelines)

Check out the first posts there..

New Israeli anti-spam law

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[Disclaimer: I'm no lawyer, please correct me if the info here is wrong]

I was surprised to read about the "spam revolution" that's about to happen on November 2008.
In short, sending spam without recipient permissions would:

  • Be illegal, with a 60,000-200,000 NIS fine.
  • Each recipient will be able to sue the spammer and get up to 1000 NIS, without the need to proof that any damage was made.

More about it (Hebrew):

Sounds great, eh?