Today's Unix Trivia

[yesthattom]

If you write to a file that is SUID or SGID, the SUID / SGID bits on the file are removed as a security precaution against tampering (unless uid 0 is doing the writing).

(See FreeBSD 5.4 source code, sys/ufs/ffs/ffs_vnops.c:739)

Comments

[rainbear.livejournal.com]

Hmm. That explains why that kept happening at Lumeta with the SGID files we had...

[rowan-redbeard.livejournal.com]

And on Solaris, you can not set the SGID bit on a directory with absolute modes with standard chmod(1). You have to use symbolic modes or the GNU equivalent. I just learned that last week.

[yesthattom.livejournal.com]

I think all Unix systems require symbolic modes for SGID and SUID.

[rowan-redbeard.livejournal.com]

Actually, we poked around and found that Solaris is the only one that does. It's particular to directories and the SGID bit, and the result is that (e.g.) "chmod 2775 " doesn't do the expected -- the "2" is ignored. Apparently FreeBSD, HPUX, and Linux all do the expected thing, but Solaris (every version we found) doesn't. This is documented in the Solaris chmod(1) man page. If you use the GNU chmod program instead, it does pay attention to the SGID bit.

[yesthattom.livejournal.com]

Thanks for the followup.