[SOLVED] Apparently, I don't understand mount

Question

Hey there!
I'm having some problems with automounting and other things, so I started working on fixing that, but first I at least want to get a few things sorted out.
For example, when I want to mount a CD-ROM, what I currently do is this:
1) start thunar in _root_ mode, if I don't do it in root it complains with a HAL error that it can't do it
2) click the CD icon in left pane
3) do my stuff (usually start smplayer )
To unmount, I just type "sudo umount /media/dvd"
Now, I was going to check on this HAL issue, but then a friend of mine alerted me to the fact that I shouldn't even be using sudo to mount.
I was curious as to why, it seems logical to need root privileges for something like that.
But then he told me about executable permissions, my mount had "-rwxr-xr-x", his had "-rwsr-xr-x". He told me about the "s" flag and how it makes the system think that you're root
when you execute it without sudo, even if you're not. So I changed the permissions on my /bin/mount. It still wouldn't work, it told me I needed to be root to mount. Then I changed the group of the
executable to "storage" instead of "root". Still no dice (even though my user is a member of storage).
I'd like to get this minor niggle fixed first before I try to even contemplate tackling the horrible mess that is udev/hal (I don't understand anything about it).
Thanks in advance!
Last edited by Aktau (2009-05-25 16:03:49)

Answer 1

Mr.Elendig wrote:
Aktau wrote:
Thanks for your replies!
Do you perhaps know why my mount just will not work without sudo? even though I have the "s" flag in user en the "x" flag in group and user? I'd really like to understand the fundamental issue here.
Once again, thanks for your swift and helpful replies, it's much appreciated.
You can only use mount and umount on a mount point, as a user, if it's in fstab with the 'user' or 'users' option. This is a security feature to prevent users from doing nasty things.
Hmmm, it makes sense from a security point of view.
I've also been digging around in the mount source code, some of the strange things I've encountered while using it that are in the source:
LINE: 918 in mount.c
switch (mnt_err) {
case EPERM:
if (geteuid() == 0) {
if (stat (node, &statbuf) || !S_ISDIR(statbuf.st_mode))
error (_("mount: mount point %s is not a directory"), node);
else
error (_("mount: permission denied"));
} else {
error (_("mount: must be superuser to use mount"));
break;
I've gotten the "mount: must be superuser to use mount" error at least once. This is really strange, as now it's checking on effective uid, which should be root for me
LINE: 1616 in mount.c
if (getuid () != geteuid ()) {
suid = 1;
if (types || options || readwrite || nomtab || mount_all ||
fake || mounttype || (argc + specseen) != 1)
die (EX_USAGE, _("mount: only root can do that"));
Look at those conditions, that's just damn weird. These are both single occurences btw, so I know I've made it that far in the code path
Last edited by Aktau (2009-05-25 15:22:31)