While replacing sendmail on a system using GNU fileutils 4.something I encountered something that surprised me. I did a "make install" of our version of mmdf, which does a "cp blah /usr/sbin/sendmail ; chown mmdf /usr/sbin/sendmail ; chmod u+s /usr/sbin/sendmail" Now, /usr/sbin/sendmail was a symlink (which I knew), which eventually resolves to /usr/sbin/sendmail.sendmail. After the install I ended up with the following: lrwxrwxrwx 1 mmdf mail 21 Dec 13 22:50 /usr/sbin/sendmail -> /etc/alternatives/mta -rwsr-xr-x 1 root smmsp 522779 Mar 20 14:53 /usr/sbin/sendmail.sendmail Note that while the symlink was chowned it was the target of the symlink that was chmoded. This resulted in a suid root file that should have been suid mmdf! Solaris, AIX, and FreeBSD all seem to have less suprising behaviour for chown and chmod and provide a "-h" flag for chowning a symlink rather than its target. Fileutils also has a "-h" flag, but it is the default for chown, so you need to say "--dereference" to get it to operate on the target. (Though there seems to be a stat/lstat bug in coreutils 5.2.1. If you run this as root: ln -s b a ; touch b ; chown dwmalone a ; chown --dereference dwmalone a then b ends up owned by root rather than dwmalone). While this choice of default isn't clearly wrong, I found it surprising. I had a look to see if this had been discussed before. All I turned up was the fileutils FAQ entry, included below, which seems to be at odds with "-h" being the default for chown. This choice of behaviour still exists in coreutile 5.2.1 as far as I can see. David. --- How do I change the ownership or permissions of a symlink? The owner, group, and permissions of a symlink are not in any way significant. Only the value of the symlink is meaningful. Regardless of that some operating systems will allow you change the owner, group or mode of a symlink and other operating systems will not. Do not worry about it as it does not matter in any case. ---
