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user_namespaces.7: Explain uid_map and gid_map in the initial user namespace 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2013-03-01 16:31:19 +01:00
parent 3e2a37ec85
commit 20e4a14719
1 changed files with 21 additions and 0 deletions
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man7/user_namespaces.7
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@ -235,6 +235,27 @@ When a process retrieves file user and group IDs via
.BR stat (2)
the IDs are mapped in the opposite direction,
to produce values relative to the process user and group ID mappings.
The initial user namespace has no parent namespace,
but, for consistency, the kernel provides dummy user and group
ID mapping files for this namespace.
Looking at the
.I uid_map
file (the
.I gid_map
is the same) from a shell in the initial namespace shows:
.in +4n
.nf
$ \fBcat /proc/$$/uid_map\fP
0 0 4294967295
.fi
.in
This mapping tells us
that the range starting at user ID 0 in this namespace
maps to a range starting at 0 in the (nonexistent) parent namespace,
and the length of the range is the largest 32-bit unsigned integer.
.\"
.\" ============================================================
.\"