# proc_pid_root - symbolic link to root directory - man(5) - [phpMan]

[_proc_pid_root_(5)](https://www.chedong.com/phpMan.php/man/procpidroot/5/markdown)                         File Formats Manual                        [_proc_pid_root_(5)](https://www.chedong.com/phpMan.php/man/procpidroot/5/markdown)

## 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)](https://www.chedong.com/phpMan.php/man/chroot/2/markdown) 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)](https://www.chedong.com/phpMan.php/man/pthreadexit/3/markdown)).

              Permission  to  dereference  or read ([**readlink**(2)](https://www.chedong.com/phpMan.php/man/readlink/2/markdown)) this symbolic link is governed by a
              ptrace access mode **PTRACE_MODE_READ_FSCREDS **check; see [**ptrace**(2)](https://www.chedong.com/phpMan.php/man/ptrace/2/markdown).

## SEE ALSO
       [**proc**(5)](https://www.chedong.com/phpMan.php/man/proc/5/markdown)

Linux man-pages 6.7                          2023-08-15                             [_proc_pid_root_(5)](https://www.chedong.com/phpMan.php/man/procpidroot/5/markdown)