How to check whether a particular directory is a mount point?

Question

How to check whether or not a particular directory is a mount point? For instance there is a folder named /test that exists, and I want to check if it is a mount point or not.

Answer 1

If you want to check it's the mount point of a file system, that's what the mountpoint command (on most Linux-based systems) is for:

if mountpoint -q -- "$dir"; then
  printf '%s\n' "$dir is a mount point"
fi

It does that by checking whether . and .. have the same device number (st_dev in stat() result). So if you don't have the mountpoint command, you could do:

perl -le '$dir = shift; exit(1) unless
  (@a = stat "$dir/." and @b = stat "$dir/.." and
  ($a[0] != $b[0] || $a[1] == $b[1]))' "$dir"

Like mountpoint, it will return true for / even if / is not a mount point (like when in a chroot jail), or false for a mount point of a bind mount of the same file system within itself.

Contrary to mountpoint, for symbolic links, it will check whether the target of the symlink is a mountpoint.

Answer 2

As HalosGhost mentions in the comments, directories aren't necessarily mounted per se. Rather they're present on a device which has been mounted. To check for this you can use the df command like so:

$ df -h /boot/
Filesystem            Size  Used Avail Use% Mounted on
/dev/hda1              99M   55M   40M  59% /boot

Here we can see that the directory /boot is part of the filesystem, /dev/hda1. This is a physical device, on the system, a HDD.

You can also come at this a little bit differently by using the mount command to query the system to see what devices are currently mounted:

$ mount | column -t
/dev/mapper/VolGroup00-LogVol00  on  /                         type  ext3         (rw)
proc                             on  /proc                     type  proc         (rw)
sysfs                            on  /sys                      type  sysfs        (rw)
devpts                           on  /dev/pts                  type  devpts       (rw,gid=5,mode=620)
/dev/hda1                        on  /boot                     type  ext3         (rw)
tmpfs                            on  /dev/shm                  type  tmpfs        (rw)
/dev/mapper/lvm--raid-lvm0       on  /export/raid1             type  ext3         (rw)
none                             on  /proc/sys/fs/binfmt_misc  type  binfmt_misc  (rw)
sunrpc                           on  /var/lib/nfs/rpc_pipefs   type  rpc_pipefs   (rw)
nfsd                             on  /proc/fs/nfsd             type  nfsd         (rw)

Here you can see the type of device and the type of filesystems are currently mounted on your system. The 3rd column shows where they're mounted on the system within its filesystem.

Answer 3

I was looking for the same question when I wanted to check mounting a new XFS filesystem.

I found the command findmnt: findmnt /directoryname

[root@CentOS7-Server /]# findmnt /mnt
TARGET SOURCE    FSTYPE OPTIONS
/mnt   /dev/sdb1 xfs    rw,relatime,seclabel,attr2,inode64,noquota
[root@CentOS7-Server /]# 

Answer 4

Well, as others said you should edit your question and make it clear on what you are trying to achieve. As far as I understood, you need to check if a directory is mounted to a particular device. You can try something like below as well.

df -P /test | tail -1 | cut -d' ' -f 1

So basically, the above command lets you know the mount point of the directory if at all the device is mounted to a directory.

Answer 5

Nice and short Python one-liner can be constructed based on Gilles' answer:

$ python -c 'import os,sys;print(os.path.ismount(sys.argv[1]))' /mnt/HDD
True

$ python -c 'import os,sys;print(os.path.ismount(sys.argv[1]))' /etc                
False

I've made custom implementation of mountpoint command in Python, which parses /proc/self/mounts file. Kind of the same behavior as mount in Stephane's answer, except that command parses /proc/self/mountinfo. Usage is very simple: is_mountpoint.py /path/to/dir.

#!/usr/bin/env python3
from os import path
import sys

def main():

    if not sys.argv[1]:
       print('Missing a path')
       sys.exit(1)

    full_path = path.realpath(sys.argv[1])
    with open('/proc/self/mounts') as mounts:
       print
       for line in mounts:
           if full_path in line:
              print(full_path,' is mountpoint')
              sys.exit(0)
    print(full_path,' is not a mountpoint')
    sys.exit(1)

if __name__ == '__main__':
    main()

Test run:

$ python3 ./is_mountpoint.py /mnt/HDD                                          
/mnt/HDD  is mountpoint
$ lsblk | grep HDD
└─sdb6   8:22   0 405.3G  0 part /mnt/HDD
$ python3 ./is_mountpoint.py $HOME                                             
/home/xieerqi  is not a mountpoint

Answer 6

Your question is little bit confusing, but I guess, one of the ways to check that: mount |awk '{print $3}'| grep -w <your_directory>. If output is empty then no device mounted to the directory . If not empty then some device mounted to the directory. Other way is to use df <your_directory>. If last field equals to your directory name - than some device is mounted to it.