Description of problem: Use of the pam_namespace.so module can result in significant differences between the /etc/mtab file reports and the state of the name-space posessed by a user's session. If the administrator mounts or umounts a file system after a user has logged in then /etc/mtab will be immediately updated but the actual mount list that applies to the user will not change. This means that "df" will produce incorrect and misleading answers. If /etc/mtab is made a symlink to /proc/mounts then the "df" command (and other programs that use /etc/mtab) will get the correct data that refers to the session in question. Also please note that pam_namespace.so provides greater benefits to non-SE Linux users than it does to SE Linux users.
/etc/mtab and /proc/mounts don't contain identical data and different apps work with them, so I don't think we can just merge them. regards, Florian La Roche