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user_namespaces.7: Document /proc/PID/projid_map 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk 2021-08-16 01:59:42 +02:00
parent 6486faa956
commit 213e259e97
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man7/user_namespaces.7
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@ -669,6 +669,48 @@ Writes that violate the above rules fail with the error
.\"
.\" ============================================================
.\"
.SS Project ID mappings: projid_map
Similarly to user and group ID mappings,
it is possible to create project ID mappings for a user namespace.
(Project IDs are used for disk quotas; see
.BR setquota (8)
and
.BR quotactl (2).)
.PP
Project ID mappings are defined by writing to the
.I /proc/[pid]/projid_map
file (present since
.\" commit f76d207a66c3a53defea67e7d36c3eb1b7d6d61d
Linux 3.7).
.PP
The validity rules for writing to the
.I /proc/[pid]/projid_map
file are as for writing to the
.I uid_map
file; violation of these rules causes
.BR write (2)
to fail with the error
.BR EINVAL .
.PP
The permission rules for writing to the
.I /proc/[pid]/projid_map
file are as follows:
.IP 1. 3
The writing process must either be in the user namespace of the process
.I pid
or be in the parent user namespace of the process
.IR pid .
.IP 2.
The mapped project IDs must in turn have a mapping
in the parent user namespace.
.PP
Violation of these rules causes
.BR write (2)
to fail with the error
.BR EPERM .
.\"
.\" ============================================================
.\"
.SS Interaction with system calls that change process UIDs or GIDs
In a user namespace where the
.I uid_map