After around 19 years, the behavior of pivot_root() has not been
changed, and will almost certainly not change in the future.
So, reword to remove the suggestion that the behavior may change.
Also, more clearly document the effect of pivot_root() on
the calling process's current working directory.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The reference of "Note that this also applies" was vague. So
combine this paragraph with an earlier one to make the linkage
clearer.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The idea that there might one day be a mechanism for kernel
threads to explicitly relinquish access to the filesystem never
came to pass (after 20 years), and the presence of text
describing this idea is, IMO, a distraction. So, remove it.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
One kernel printk() later, my suspicions seem confirmed: the text
describing the situation where the current root is not a mount
point (because of a chroot()) seems to be bogus. (Perhaps it was
true once upon a time.) In my testing, if the current root is not
a mount point, an EINVAL error results.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
In this text:
If the current root is not a mount point (e.g., after an
earlier chroot(2) or pivot_root())...
mention of pivot_root() makes no sense, since (as noted in an
earlier commit message for this page) 'new_root' in a previous
pivot_root() must (since Linux 2.4.5) have been a mount point.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
One of these "bugs" is a philosophical point already covered
elsewhere in the page, while the other is a somewhat obscure joke.
Both pieces are a bit of a distraction, really.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The note that EBUSY is given if a filesystem is already mounted
on 'Iput_old' was never really true. That restriction was in
Linux 2.3.14, but removed in Linux 2.3.99-pre6 so it never made
it to mainline.
The relevant diff in pivot_root() was:
error = -EBUSY;
- if (d_new_root->d_sb == root->d_sb || d_put_old->d_sb == root->d_sb)
+ if (new_nd.mnt == root_mnt || old_nd.mnt == root_mnt)
goto out2; /* loop */
- if (d_put_old != d_put_old->d_covers)
- goto out2; /* mount point is busy */
error = -EINVAL;
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Some of the text was written long ago, and hinted that things
might change in the future. However, 20 years have passed
and these details have not changed, so rework the text to
hint at that fact.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
As far as I can see from the source code, the statement that
"No other filesystem may be mounted on 'put_old'" is incorrect.
Even looking at the 2.4.0 source code, there I can't see such
a restriction. In addition, some testing on a 5.0 kernel
(mounting 'put_old' in the new mount namespace just before
pivot_root()) did not result in an error for this case when
calling pivot_root().
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
pivot_root() only affects the current working directory and root
directory of other processes in the same mount namespace as the
caller.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The restriction on what values may be specified in 'si_code'
apply only when sending a signal to a process other than the
caller itself.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Threads are allowed to switch mount namespaces if the filesystem
details aren't being shared. That's the purpose of the check in
the kernel quoted by the comment:
if (fs->users != 1)
return -EINVAL;
It's been this way since the code was originally merged in v3.8.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Since introduction of MAP_SHARED_VALIDATE, in case flags contain
both MAP_PRIVATE and MAP_SHARED, mmap() doesn't fail with EINVAL,
it succeeds.
The reason for that is that MAP_SHARED_VALIDATE is in fact equal
to MAP_PRIVATE | MAP_SHARED.
This is intended behavior, see:
https://lwn.net/Articles/758594/https://lwn.net/Articles/758598/
Signed-off-by: Nikola Forró <nforro@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Things changed in Linux v5.3-rc3 commit 315c69261dd3 from
splitting after template expansion to splitting beforehand.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This requirement on the first digit with the %e format comes from
the ISO C standard. It ensures that all the digits in the output are
significant and forbids output with a precision less than requested.
Signed-off-by: Vincent Lefevre <vincent@vinc17.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk