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From: Michael Kerrisk <mtk.manpages@gmail.com>
To: mtk.manpages@gmail.com, Karel Zak <kzak@redhat.com>
Cc: util-linux@vger.kernel.org
Subject: [PATCH 7/9] Manual pages: unshare.1: fix examples, part 1
Date: Sat, 23 May 2020 08:43:23 +0200
Message-ID: <20200523064325.78491-7-mtk.manpages@gmail.com> (raw)
In-Reply-To: <20200523064325.78491-1-mtk.manpages@gmail.com>

The examples section of this manual page is rather hard to grok.
First, the arrangement of the text as follows makes life harder
than needed for the reader:

    shell demo
        explanatory text

It helps the reader if an example *begins* with an explanation of
what is being demonstrated. Therefore, rearrange these examples as:

    explanatory text
        shell demo

In addition, let's provide a bit more explanation for the first three
examples and expand the second example (user namespaces) a little.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
---
 sys-utils/unshare.1 | 109 +++++++++++++++++++++++++++++---------------
 1 file changed, 72 insertions(+), 37 deletions(-)

diff --git a/sys-utils/unshare.1 b/sys-utils/unshare.1
index 14b107d37..b8ef371a0 100644
--- a/sys-utils/unshare.1
+++ b/sys-utils/unshare.1
@@ -244,61 +244,96 @@ restricted so that a less privileged user can not get more access to sensitive
 files that a more privileged user made unavailable. In short the rule for proc
 and sysfs is as close to a bind mount as possible.
 .SH EXAMPLE
-.TP
+.PP
+The following command creates a PID namespace, using
+.B \-\-fork
+to ensure that the executed command is performed in a child process
+that (being the first process in the namespace) has PID 1.
+The
+.B \-\-mount-proc
+option ensures that a new mount namespace is also simultaneously created
+and that a new
+.BR proc (5)
+filesystem is mounted that contains information corresponding to the new
+PID namespace.
+When the
+.BR readlink
+command terminates, the new namespaces are automatically torn down.
+.PP
+.in +4n
+.EX
 .B # unshare \-\-fork \-\-pid \-\-mount-proc readlink /proc/self
-.TQ
 1
-.br
-Establish a PID namespace, ensure we're PID 1 in it against a newly mounted
-procfs instance.
-.TP
-.B $ unshare \-\-map-root-user \-\-user sh \-c whoami
-.TQ
+.EE
+.in
+.PP
+As an unprivileged user, create a new user namespace where the user's
+credentials are mapped to the root IDs inside the namespace:
+.PP
+.in +4n
+.EX
+.B $ id \-u; id \-g
+1000
+1000
+.B $ unshare \-\-user \-\-map-root-user \e
+.B "        sh \-c \(aqwhoami; cat /proc/self/uid_map /proc/self/gid_map\(aq"
 root
-.br
-Establish a user namespace as an unprivileged user with a root user within it.
-.TP
+         0       1000          1
+         0       1000          1
+.EE
+.in
+.PP
+The first of the following commands creates a new persistent UTS namespace
+and modifies the hostname as seen in that namespace.
+The namespace is then entered with
+.BR nsenter (1)
+in order to display the modified hostname;
+this step demonstrates that the UTS namespace continues to exist
+even though the namespace had no member processes after the
+.B unshare
+command terminated.
+The namespace is then destroyed by removing the bind mount.
+.PP
+.in +4n
+.EX
 .B # touch /root/uts-ns
-.TQ
 .B # unshare \-\-uts=/root/uts-ns hostname FOO
-.TQ
 .B # nsenter \-\-uts=/root/uts-ns hostname
-.TQ
 FOO
-.TQ
 .B # umount /root/uts-ns
-.br
-Establish a persistent UTS namespace, and modify the hostname.  The namespace
-is then entered with \fBnsenter\fR.  The namespace is destroyed by unmounting
-the bind reference.
-.TP
+.EE
+.in
+.PP
+Establish a persistent mount namespace referenced by the bind mount
+/root/namespaces/mnt.  This example shows a portable solution, because it
+makes sure that the bind mount is created on a shared filesystem.
+.PP
+.in +4n
+.EX
 .B # mount \-\-bind /root/namespaces /root/namespaces
-.TQ
 .B # mount \-\-make-private /root/namespaces
-.TQ
 .B # touch /root/namespaces/mnt
-.TQ
 .B # unshare \-\-mount=/root/namespaces/mnt
-.br
-Establish a persistent mount namespace referenced by the bind mount
-/root/namespaces/mnt.  This example shows a portable solution, because it
-makes sure that the bind mount is created on a shared filesystem.
-.TP
-.B # unshare \-pf \-\-kill-child \-\- bash \-c "(sleep 999 &) && sleep 1000" &
-.TQ
-.B # pid=$!
-.TQ
-.B # kill $pid
-.br
+.EE
+.in
+.PP
 Reliable killing of subprocesses of the \fIprogram\fR.
 When \fBunshare\fR gets killed, everything below it gets killed as well.
 Without it, the children of \fIprogram\fR would have orphaned and
 been re-parented to PID 1.
-.TP
+.PP
+.in +4n
+.EX
+.B # unshare \-pf \-\-kill-child \-\- bash \-c "(sleep 999 &) && sleep 1000" &
+.B # pid=$!
+.B # kill $pid
+.EE
+.in
+.PP
+.in +4n
+.EX
 .B # unshare \-\-fork \-\-time \-\-boottime 100000000 uptime
-.TQ
  10:58:48 up 1158 days,  6:05,  1 user,  load average: 0.00, 0.00, 0.00
-
 .SH AUTHORS
 .UR dottedmag@dottedmag.net
 Mikhail Gusarov
-- 
2.26.2


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-23  6:43 [PATCH 1/9] Manual pages: nsenter.1, unshare.1: update references to *_namespaces(7) pages Michael Kerrisk
2020-05-23  6:43 ` [PATCH 2/9] Manual pages: nsenter.1, unshare.1: add a reference to time_namespaces(7) Michael Kerrisk
2020-05-23  6:43 ` [PATCH 3/9] Manual pages: nsenter.1, unshare.1: remove repeated references to clone(2) Michael Kerrisk
2020-05-23  6:43 ` [PATCH 4/9] Manual pages: unshare.1: improve intro paragraphs Michael Kerrisk
2020-05-23  6:43 ` [PATCH 5/9] Manual pages: nsenter.1: clarify the intro discussion Michael Kerrisk
2020-05-23  6:43 ` [PATCH 6/9] Manual pages: nsenter.1: note that 'file' can be a bind mount Michael Kerrisk
2020-05-23  6:43 ` Michael Kerrisk [this message]
2020-05-23  6:43 ` [PATCH 8/9] Manual pages: unshare.1: fix examples, part 2 Michael Kerrisk
2020-05-23  6:43 ` [PATCH 9/9] Manual pages: unshare.1: fix examples, part 3 Michael Kerrisk
2020-05-25 12:17 ` [PATCH 1/9] Manual pages: nsenter.1, unshare.1: update references to *_namespaces(7) pages Karel Zak
2020-05-25 13:13   ` Michael Kerrisk (man-pages)
2020-05-26  8:50     ` Karel Zak
2020-05-27 12:37       ` Michael Kerrisk (man-pages)

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