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.\" Copyright (C) 1994, 1995, Daniel Quinlan <quinlan@yggdrasil.com>
.\" Copyright (C) 2002-2008, 2017, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright (C) 2023, Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: GPL-3.0-or-later
.\"
.TH proc_pid 5 (date) "Linux man-pages (unreleased)"
.SH NAME
/proc/pid/, /proc/self/ \- process information
.SH DESCRIPTION
.TP
.IR /proc/ pid /
There is a numerical subdirectory for each running process; the
subdirectory is named by the process ID.
Each
.IR /proc/ pid
subdirectory contains the pseudo-files and directories described below.
.IP
The files inside each
.IR /proc/ pid
directory are normally owned by the effective user and
effective group ID of the process.
However, as a security measure, the ownership is made
.I root:root
if the process's "dumpable" attribute is set to a value other than 1.
.IP
Before Linux 4.11,
.\" commit 68eb94f16227336a5773b83ecfa8290f1d6b78ce
.I root:root
meant the "global" root user ID and group ID
(i.e., UID 0 and GID 0 in the initial user namespace).
Since Linux 4.11,
if the process is in a noninitial user namespace that has a
valid mapping for user (group) ID 0 inside the namespace, then
the user (group) ownership of the files under
.IR /proc/ pid
is instead made the same as the root user (group) ID of the namespace.
This means that inside a container,
things work as expected for the container "root" user.
.IP
The process's "dumpable" attribute may change for the following reasons:
.RS
.IP \[bu] 3
The attribute was explicitly set via the
.BR prctl (2)
.B PR_SET_DUMPABLE
operation.
.IP \[bu]
The attribute was reset to the value in the file
.I /proc/sys/fs/suid_dumpable
(described below), for the reasons described in
.BR prctl (2).
.RE
.IP
Resetting the "dumpable" attribute to 1 reverts the ownership of the
.IR /proc/ pid /*
files to the process's effective UID and GID.
Note, however, that if the effective UID or GID is subsequently modified,
then the "dumpable" attribute may be reset, as described in
.BR prctl (2).
Therefore, it may be desirable to reset the "dumpable" attribute
.I after
making any desired changes to the process's effective UID or GID.
.TP
.I /proc/self/
This directory refers to the process accessing the
.I /proc
filesystem,
and is identical to the
.I /proc
directory named by the process ID of the same process.
.SH SEE ALSO
.BR proc (5)
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