proc_pid_mountinfo - Man Page

/proc/pid/mountinfo (since Linux 2.6.26)

This file contains information about mounts in the process's mount namespace (see mount_namespaces(7)). It supplies various information (e.g., propagation state, root of mount for bind mounts, identifier for each mount and its parent) that is missing from the (older) /proc/pid/mounts file, and fixes various other problems with that file (e.g., nonextensibility, 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 a new mount is stacked on top of a previous existing mount (so that it hides the existing mount) at pathname P, then the parent of the new mount is the previous mount at that location. Thus, when looking at all the mounts stacked at a particular location, the top-most mount is the one that is not the parent of any other mount at the same location. (Note, however, that this top-most mount will be accessible only if the longest path subprefix of P that is a mount point is not itself hidden by a stacked mount.)

If the parent mount 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 mounts 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 may have a parent mount (for the initramfs filesystem) that lies outside the process's root directory, and an entry for that mount 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 (see mount(2)).

(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 (see mount(2)).

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 unrecognized optional fields.

For more information on mount propagation see Documentation/filesystems/sharedsubtree.rst (or Documentation/filesystems/sharedsubtree.txt before Linux 5.8) in the Linux kernel source tree.

proc(5)