для чего/proc/1/mountinfo файл?

О proc файловой системе
https://en.wikipedia.org/wiki/Procfs
http://tldp.org/LDP/sag/html/proc-fs.html
Ниже извлечения http://man7.org/linux/man-pages/man5/proc.5.html

   /proc/[pid]/mountinfo (since Linux 2.6.26)
          This file contains information about mount points in the
          process's mount namespace (see mount_namespaces(7)).  It sup‐
          plies various information (e.g., propagation state, root of
          mount for bind mounts, identifier for each mount and its par‐
          ent) that is missing from the (older) /proc/[pid]/mounts file,
          and fixes various other problems with that file (e.g., nonex‐
          tensibility, failure to distinguish per-mount versus per-
          superblock options).

          The file contains lines of the form:

36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)

          The numbers in parentheses are labels for the descriptions
          below:

          (1)  mount ID: a unique ID for the mount (may be reused after
               umount(2)).

          (2)  parent ID: the ID of the parent mount (or of self for the
               root of this mount namespace's mount tree).

               If the parent mount point lies outside the process's root
               directory (see chroot(2)), the ID shown here won't have a
               corresponding record in mountinfo whose mount ID (field
               1) matches this parent mount ID (because mount points
               that lie outside the process's root directory are not
               shown in mountinfo).  As a special case of this point,
               the process's root mount point may have a parent mount
               (for the initramfs filesystem) that lies outside the
               process's root directory, and an entry for that mount
               point will not appear in mountinfo.

          (3)  major:minor: the value of st_dev for files on this
               filesystem (see stat(2)).

          (4)  root: the pathname of the directory in the filesystem
               which forms the root of this mount.

          (5)  mount point: the pathname of the mount point relative to
               the process's root directory.

          (6)  mount options: per-mount options.

          (7)  optional fields: zero or more fields of the form
               "tag[:value]"; see below.

          (8)  separator: the end of the optional fields is marked by a
               single hyphen.

          (9)  filesystem type: the filesystem type in the form
               "type[.subtype]".

          (10) mount source: filesystem-specific information or "none".

          (11) super options: per-superblock options.

          Currently, the possible optional fields are shared, master,
          propagate_from, and unbindable.  See mount_namespaces(7) for a
          description of these fields.  Parsers should ignore all unrec‐
          ognized optional fields.

          For more information on mount propagation see: Documenta‐
          tion/filesystems/sharedsubtree.txt in the Linux kernel source
          tree.