proc_pid_root - symbolic link to root directory
NAME DESCRIPTION SEE ALSONAME
/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).
SEE ALSO
proc(5)