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namespaces.7: Document some disallowed cases for CLONE_NEWPID + CLONE_VM 

Based on text from Eric Biederman

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2013-01-14 09:28:37 +01:00
parent e7d2eab5d3
commit 857c57e70d
1 changed files with 22 additions and 0 deletions
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man7/namespaces.7
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@ -387,6 +387,28 @@ then it isn't necessary to change the root directory:
a new procfs instance can be mounted directly over
.IR /proc .)
Every thread in a process must be in the same PID namespace.
For this reason, the two following call sequences will fail:
.in +4n
.nf
unshare(CLONE_NEWPID);
clone(..., CLONE_VM, ...); /* Fails */
setns(fd, CLONE_NEWPID);
clone(..., CLONE_VM, ...); /* Fails */
.fi
.in
Because the above
.BR unshare (2)
and
.BR setns (2)
calls only change the PID namespace for created children, the
.BR clone (2)
calls necessarily put the new thread in a different PID namespace from
the calling thread.
Use of PID namespaces requires a kernel that is configured with the
.B CONFIG_PID_NS
option.