Man page - proc_pid_root(5)

Packages contains this manual

Package: manpages
apt-get install manpages

Manuals in package:

Documentations in package:

manpages

Available languages:

en fr pl ro de

Manual

proc_pid_root

NAME
DESCRIPTION
SEE ALSO

NAME

/proc/pid/root/ - symbolic link to root directory

DESCRIPTION

/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).