mirror of https://github.com/mkerrisk/man-pages
mount_namespaces.7: Minor tweaks
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk
parent
98c28960c3
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d9cdf357c9
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@ -89,12 +89,12 @@ as having one of the following
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.BR MS_SHARED
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This mount point shares events with members of a peer group.
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Mount and unmount events immediately under this mount point will propagate
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outward to the other mount points that are members of the peer group.
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to the other mount points that are members of the peer group.
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.I Propagation
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here means that the same mount or unmount will automatically occur
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under all of the other mount points in the peer group.
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Conversely, mount and unmount events that take place under
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peer mount points will propagate inward to this mount point.
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peer mount points will propagate to this mount point.
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.TP
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.BR MS_PRIVATE
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This mount point is private; it does not have a peer group.
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@ -176,10 +176,11 @@ for a record in that file:
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.I shared:X
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This mount point is shared in peer group
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.IR X .
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Each peer group has a unique ID (a small integer) that is automatically
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Each peer group has a unique ID that is automatically
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generated by the kernel,
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and all mount points in the same peer group will show the same ID.
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(These IDs may be recycled when a peer group ceases to have any members.)
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(These IDs are assigned starting from the value 1,
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and may be recycled when a peer group ceases to have any members.)
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.TP
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.I master:X
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This mount is a slave to shared peer group
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@ -217,27 +218,27 @@ and then view the mounts in
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.nf
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.in +4n
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sh1# \fBmount \-\-make\-private /mntB\fP
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sh1# \fBmount \-\-make\-shared /mntA\fP
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sh1# \fBmount \-\-make\-shared /mntS\fP
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sh1# \fBmount \-\-make\-private /mntP\fP
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sh1# \fBcat /proc/self/mountinfo | grep \(aq/mnt[AB]\(aq | sed \(aqs/ \- .*//\(aq\fP
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77 61 8:17 / /mntA rw,relatime shared:1
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83 61 8:15 / /mntB rw,relatime
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77 61 8:17 / /mntS rw,relatime shared:1
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83 61 8:15 / /mntP rw,relatime
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.in
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.fi
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From the
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.IR /proc/self/mountinfo
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output, we see that
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.IR /mntA
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.IR /mntS
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is a shared mount in peer group 1, and that
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.IR /mntB
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.IR /mntP
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has no optional tags, indicating that it is a private mount.
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The first two fields in each record in this file are the unique
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ID for this mount, and the mount ID of the parent mount.
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We can further inspect this file to see that the parent mount point of
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.IR /mntA
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.IR /mntS
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and
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.IR /mntB
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.IR /mntP
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is the root directory,
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.IR / ,
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which is mounted as private:
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@ -257,8 +258,8 @@ and inspect the mounts:
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.in +4n
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$ \fBPS1=\(aqsh2# \(aq sudo unshare \-m \-\-propagation unchanged sh\fP
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sh2# \fBcat /proc/self/mountinfo | grep \(aq/mnt[AB]\(aq | sed \(aqs/ \- .*//\(aq\fP
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222 145 8:17 / /mntA rw,relatime shared:1
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225 145 8:15 / /mntB rw,relatime
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222 145 8:17 / /mntS rw,relatime shared:1
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225 145 8:15 / /mntP rw,relatime
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.in
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.fi
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@ -275,52 +276,52 @@ from marking all mounts as private when creating a new mount namespace,
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which it does by default.)
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In the second terminal, we then create submounts under each of
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.IR /mntA
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.IR /mntS
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and
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.IR /mntB
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.IR /mntP
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and inspect the set-up:
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.nf
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.in +4n
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sh2# \fBmkdir /mntA/x\fP
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sh2# \fBmount /dev/sdb6 /mntA/x\fP
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sh2# \fBmkdir /mntB/y\fP
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sh2# \fBmount /dev/sdb7 /mntB/y\fP
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sh2# \fBmkdir /mntS/a\fP
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sh2# \fBmount /dev/sdb6 /mntS/a\fP
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sh2# \fBmkdir /mntP/b\fP
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sh2# \fBmount /dev/sdb7 /mntP/b\fP
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sh2# \fBcat /proc/self/mountinfo | grep \(aq/mnt[AB]\(aq | sed \(aqs/ \- .*//\(aq\fP
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222 145 8:17 / /mntA rw,relatime shared:1
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225 145 8:15 / /mntB rw,relatime
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178 222 8:22 / /mntA/x rw,relatime shared:2
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230 225 8:23 / /mntB/y rw,relatime
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222 145 8:17 / /mntS rw,relatime shared:1
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225 145 8:15 / /mntP rw,relatime
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178 222 8:22 / /mntS/a rw,relatime shared:2
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230 225 8:23 / /mntP/b rw,relatime
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.in
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.fi
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From the above, it can be seen that
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.IR /mntA/x
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.IR /mntS/a
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was created as shared (inheriting this setting from its parent mount) and
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.IR /mntB/y
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.IR /mntP/b
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was created as a private mount.
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Returning to the first terminal and inspecting the set-up,
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we see that the new mount created under the shared mount point
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.IR /mntA
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.IR /mntS
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propagated to its peer mount (in the initial mount namespace),
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but the new mount created under the private mount point
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.IR /mntB
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.IR /mntP
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did not propagate:
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.nf
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.in +4n
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sh1# \fBcat /proc/self/mountinfo | grep \(aq/mnt[AB]\(aq | sed \(aqs/ \- .*//\(aq\fP
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77 61 8:17 / /mntA rw,relatime shared:1
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83 61 8:15 / /mntB rw,relatime
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179 77 8:22 / /mntA/x rw,relatime shared:2
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77 61 8:17 / /mntS rw,relatime shared:1
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83 61 8:15 / /mntP rw,relatime
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179 77 8:22 / /mntS/a rw,relatime shared:2
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.in
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.fi
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.\"
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.SS MS_SLAVE example
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Making a mount point a slave allows it to receive propagated
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mount and unmount events from a master shared peer group,
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while preventing it from propagating events outward to that master.
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while preventing it from propagating events to that master.
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This is useful if we want to (say) receive a mount event when
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an optical disk is mounted in the master shared peer group
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(in another mount namespace),
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@ -375,19 +376,19 @@ and
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.nf
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.in +4n
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sh2# \fBmkdir /mntX/aaa\fP
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sh2# \fBmount /dev/sda3 /mntX/aaa\fP
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sh2# \fBmkdir /mntY/bbb\fP
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sh2# \fBmount /dev/sda5 /mntY/bbb\fP
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sh2# \fBmkdir /mntX/a\fP
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sh2# \fBmount /dev/sda3 /mntX/a\fP
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sh2# \fBmkdir /mntY/b\fP
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sh2# \fBmount /dev/sda5 /mntY/b\fP
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.in
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.fi
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When we inspect the state of the mount points in the new mount namespace,
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we see that
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.IR /mntX/aaa
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.IR /mntX/a
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was created as a new shared mount
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(inheriting the "shared" setting from its parent mount) and
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.IR /mntY/bbb
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.IR /mntY/b
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was created as a private mount:
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.nf
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@ -395,18 +396,18 @@ was created as a private mount:
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sh2# \fBcat /proc/self/mountinfo | grep \(aq/mnt\(aq | sed \(aqs/ \- .*//\(aq\fP
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168 167 8:23 / /mntX rw,relatime shared:1
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169 167 8:22 / /mntY rw,relatime master:2
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173 168 8:3 / /mntX/aaa rw,relatime shared:3
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175 169 8:5 / /mntY/bbb rw,relatime
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173 168 8:3 / /mntX/a rw,relatime shared:3
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175 169 8:5 / /mntY/b rw,relatime
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.in
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.fi
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Returning to the first terminal (in the initial mount namespace),
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we see that the mount
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.IR /mntX/aaa
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.IR /mntX/a
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propagated to the peer (the shared
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.IR /mntX ),
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but the mount
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.IR /mntY/bbb
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.IR /mntY/b
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was not propagated:
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.nf
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@ -414,7 +415,7 @@ was not propagated:
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sh1# \fBcat /proc/self/mountinfo | grep \(aq/mnt\(aq | sed \(aqs/ \- .*//\(aq\fP
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132 83 8:23 / /mntX rw,relatime shared:1
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133 83 8:22 / /mntY rw,relatime shared:2
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174 132 8:3 / /mntX/aaa rw,relatime shared:3
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174 132 8:3 / /mntX/a rw,relatime shared:3
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.in
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.fi
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@ -424,13 +425,13 @@ in the first shell:
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.nf
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.in +4n
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sh1# \fBmkdir /mntY/ccc\fP
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sh1# \fBmount /dev/sda1 /mntY/ccc\fP
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sh1# \fBmkdir /mntY/c\fP
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sh1# \fBmount /dev/sda1 /mntY/c\fP
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sh1# \fBcat /proc/self/mountinfo | grep '/mnt' | sed 's/ \- .*//'\fP
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132 83 8:23 / /mntX rw,relatime shared:1
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133 83 8:22 / /mntY rw,relatime shared:2
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174 132 8:3 / /mntX/aaa rw,relatime shared:3
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178 133 8:1 / /mntY/ccc rw,relatime shared:4
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174 132 8:3 / /mntX/a rw,relatime shared:3
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178 133 8:1 / /mntY/c rw,relatime shared:4
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.in
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.fi
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@ -444,9 +445,9 @@ and that the new mount is itself a slave mount (to peer group 4):
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sh2# \fBcat /proc/self/mountinfo | grep \(aq/mnt\(aq | sed \(aqs/ \- .*//\(aq\fP
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168 167 8:23 / /mntX rw,relatime shared:1
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169 167 8:22 / /mntY rw,relatime master:2
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173 168 8:3 / /mntX/aaa rw,relatime shared:3
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175 169 8:5 / /mntY/bbb rw,relatime
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179 169 8:1 / /mntY/ccc rw,relatime master:4
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173 168 8:3 / /mntX/a rw,relatime shared:3
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175 169 8:5 / /mntY/b rw,relatime
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179 169 8:1 / /mntY/c rw,relatime master:4
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.in
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.fi
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.\"
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