proc_pid_mountinfo(5) File Formats Manual proc_pid_mountinfo(5)
NAME
/proc/pid/mountinfo - mount information
DESCRIPTION
/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 dis-
tinguish 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 direc-
tory (see chroot(2)), the ID shown here won't have a corre-
sponding record in mountinfo whose mount ID (field 1)
matches this parent mount ID (because mounts that lie out-
side 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 filesys-
tem (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[.sub-
type]".
(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, prop-
agate_from, and unbindable. See mount_namespaces(7) for a de-
scription of these fields. Parsers should ignore all unrecog-
nized optional fields.
For more information on mount propagation see Documenta-
tion/filesystems/sharedsubtree.rst (or Documentation/filesys-
tems/sharedsubtree.txt before Linux 5.8) in the Linux kernel
source tree.
SEE ALSO
proc(5)
Linux man-pages 6.9.1 2024-05-02 proc_pid_mountinfo(5)
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