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NAME | DESCRIPTION | SEE ALSO | COLOPHON |
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proc_pid_root(5) File Formats Manual proc_pid_root(5)
/proc/pid/root/ - symbolic link to root directory
/proc/pid/root/
UNIX and Linux support the idea of a per-process root of
the filesystem, set by the chroot(2) system call. This
file is a symbolic link that points to the process's root
directory, and behaves in the same way as exe, and fd/*.
Note however that this file is not merely a symbolic link.
It provides the same view of the filesystem (including
namespaces and the set of per-process mounts) as the
process itself. An example illustrates this point. In
one terminal, we start a shell in new user and mount
namespaces, and in that shell we create some new mounts:
$ PS1='sh1# ' unshare -Urnm
sh1# mount -t tmpfs tmpfs /etc # Mount empty tmpfs at /etc
sh1# mount --bind /usr /dev # Mount /usr at /dev
sh1# echo $$
27123
In a second terminal window, in the initial mount
namespace, we look at the contents of the corresponding
mounts in the initial and new namespaces:
$ PS1='sh2# ' sudo sh
sh2# ls /etc | wc -l # In initial NS
309
sh2# ls /proc/27123/root/etc | wc -l # /etc in other NS
0 # The empty tmpfs dir
sh2# ls /dev | wc -l # In initial NS
205
sh2# ls /proc/27123/root/dev | wc -l # /dev in other NS
11 # Actually bind
# mounted to /usr
sh2# ls /usr | wc -l # /usr in initial NS
11
In a multithreaded process, the contents of the
/proc/pid/root symbolic link are not available if the main
thread has already terminated (typically by calling
pthread_exit(3)).
Permission to dereference or read (readlink(2)) this
symbolic link is governed by a ptrace access mode
PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
proc(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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2024-06-26. If you discover any rendering problems in this HTML
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part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-05-02 proc_pid_root(5)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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