proc_pid(5) File Formats Manual proc_pid(5)
NAME
/proc/pid/, /proc/self/ - process information
DESCRIPTION
/proc/pid/
There is a numerical subdirectory for each running process; the
subdirectory is named by the process ID. Each /proc/pid subdi-
rectory contains the pseudo-files and directories described be-
low.
The files inside each /proc/pid directory are normally owned by
the effective user and effective group ID of the process. How-
ever, as a security measure, the ownership is made root:root if
the process's "dumpable" attribute is set to a value other than
1.
Before Linux 4.11, 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 name-
space that has a valid mapping for user (group) ID 0 inside the
namespace, then the user (group) ownership of the files under
/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.
The process's "dumpable" attribute may change for the following
reasons:
• The attribute was explicitly set via the prctl(2)
PR_SET_DUMPABLE operation.
• The attribute was reset to the value in the file
/proc/sys/fs/suid_dumpable (described below), for the reasons
described in prctl(2).
Resetting the "dumpable" attribute to 1 reverts the ownership of
the /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 de-
scribed in prctl(2). Therefore, it may be desirable to reset
the "dumpable" attribute after making any desired changes to the
process's effective UID or GID.
/proc/self/
This directory refers to the process accessing the /proc
filesystem, and is identical to the /proc directory named by the
process ID of the same process.
SEE ALSO
proc(5)
Linux man-pages 6.7 2023-08-15 proc_pid(5)
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