/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-ttmpfstmpfs/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#'sudosh 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/pid/root/ - symbolic link to root directory

proc(5) Linux man-pages 6.9.1 2024-05-02 proc_pid_root(5)