In the RETURN VALUE sections, a number of different wordings
are used in to describe the fact that 'errno' is set on error.
There's no reason for the difference in wordings, since the same
thing is being described in each case. Switch to a standard
wording that is the same as FreeBSD and similar to the wording
used in POSIX.1.
In this change, fix some instances stating that 'errno' is set
"appropriately" to instead say "to indicate the error".
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The majority of pages use .nf/.fi in SYNOPSIS, but there are
still many that don't and use .br to achieve newlines. Fix many
of those. This brings greater consistency to the pages, which
eases editing and may ease future scripted edits to the pages.
Many of these changes were script-assisted, with some additional
manual edits.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Use \(aq to get an unslanted single quote inside monospace code
blocks. Using a simple ' results in a slanted quote inside PDFs.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Remove superfluous paragraph macros.
Remove ".br" if it is before a line that starts with a space
character, as such lines automatically cause a break.
###
The output is unchanged, except two empty lines are added at the
bottom (before the footer line) in the output of "nroff" for the files
"alloc_hugepages.2" and "userfaultfd.2".
###
Examples of warnings from "mandoc -Tlint":
mandoc: access.2:283:2: WARNING: skipping paragraph macro: PP after SH
mandoc: adjtimex.2:185:2: WARNING: skipping paragraph macro: PP empty
mandoc: futex.2:728:2: WARNING: skipping paragraph macro: IP empty
mandoc: getsid.2:48:2: WARNING: skipping paragraph macro: br before text line with leading blank
mandoc: init_module.2:290:2: WARNING: skipping paragraph macro: PP after SS
mandoc: ioctl_fideduperange.2:27:2: WARNING: skipping paragraph macro: br after SH
Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
EXAMPLES appears to be the wider majority usage across various
projects' manual pages, and is also what is used in the POSIX
manual pages.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
After my rewriting, almost nothing of the original page remains,
so update the copyright. As the author, I'm relicensing to the
"verbatim" license most commonly used in man pages.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The text stating that "pivot_root() may or may not change the
current root and the current working directory of any processes
or threads which use the old root directory" was written 19 years
ago, before the system call itself was even finalized in the
kernel. The implementation has never changed, and it won't
change in the future, since that would cause user-space breakage.
The existence of that text in DESCRIPTION, followed by qualifying
text stating what the implementation actually does (and has always
done) makes for confusing reading. Therefore, relegate this text
to a historical note in NOTES (so that readers with long memories
can see why the manual page was changed) and rework the text in
DESCRIPTION accordingly.
Reported-by: Philipp Wendler <ml@philippwendler.de>
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Reported-by: Reid Priedhorsky <reidpr@lanl.gov>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Eric:
If we are going to be pedantic "filesystem" is really the
wrong concept here. The section about bind mount clarifies
it, but I wonder if there is a better term.
I think I would say: "new_root and put_old must not be on
the same mount as the current root."
I think using "mount" instead of "filesystem" keeps the
concepts less confusing.
As I am reading through this email and seeing text that is
trying to be precise and clear then hitting the term
"filesystem" is a bit jarring. pivot_root doesn't care a
thing for file systems. pivot_root only cares about mounts.
And by a "mount" I mean the thing that you get when you
create a bind mount or you call mount normally.
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Philipp Wendler noted that the text on the restrictions for
'new_root' was slightly contradictory, and things could be
clarified and simplified by describing the restrictions on
'new_root' in one place.
Reported-by: Philipp Wendler <ml@philippwendler.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Remove the text that suggests that pivot_root() changes the root
directory and CWD of process that have directory and CWD on the
old root *filesystem*. Change "filesystem" to "directory".
Reported-by: Philipp Wendler <ml@philippwendler.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Reid noted a confusion between 'old_root' (my attempt at a
shorthand for the old root point) and 'put_old. Eliminate the
confusion by replacing the shorthand with "old root mount point".
Reported-by: Reid Priedhorsky <reidpr@lanl.gov>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Eric Biederman notes that the change in commit f646ac88ef was
not strictly necessary for this example, since one of the already
documented requirements is that various mount points must not have
shared propagation, or else pivot_root() will fail. So, simplify
the example.
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Eric Biederman noted that my list of directories that could not
have shared propagation was incorrect. I had written that
new_root could not be shared; rather it should be: the parent of
the current root mount point.
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Eric Biederman:
The concern from our conversation at the container
mini-summit was that there is a pathology if in your initial
mount namespace all of the mounts are marked MS_SHARED like
systemd does (and is almost necessary if you are going to
use mount propagation), that if new_root itself is MS_SHARED
then unmounting the old_root could propagate.
So I believe the desired sequence is:
>>> chdir(new_root);
+++ mount("", ".", MS_SLAVE | MS_REC, NULL);
>>> pivot_root(".", ".");
>>> umount2(".", MNT_DETACH);
The change to new new_root could be either MS_SLAVE or
MS_PRIVATE. So long as it is not MS_SHARED the mount won't
propagate back to the parent mount namespace.
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
LXC uses this [1]. I tested, to double-check, and it works.
The fchdir() dance done by LXC is not needed though:
fchdir(old_root); umount(".", MNT_DETACH); fchdir(new_root);
As far as I can see, just the umount() is sufficient, since,
after pivot_root(), oldi_root is at the top of the stack
of mounts at "/" and thus (so long as CWD is at "/")
the umount will remove the mount at the top of the stack.
Eric Biederman confirmed my understanding by mail, and
Philipp Wendler verified my results by experiment.
[1] See the following commit in LXC:
commit 2d489f9e87fa0cccd8a1762680a43eeff2fe1b6e
Author: Serge Hallyn <serge.hallyn@ubuntu.com>
Date: Sat Sep 20 03:15:44 2014 +0000
pivot_root: switch to a new mechanism (v2)
Helped-by: Eric W. Biederman <ebiederm@xmission.com>
Helped-by: Philipp Wendler <ml@philippwendler.de>
Helped-by: Aleksa Sarai <asarai@suse.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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>
Alejandro Colomar