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).