Findmnt is a free and open source utility usually included in the core packages of all the major Linux distributions. It is able to list all mounted filesystems or retrieve data for only those we specify. In this tutorial, we learn how to use findmnt, and how to query filesystems by type, mount options and other parameters.
In this tutorial you will learn:
- How to use findmnt to retrieve information about mounted filesystems
- How to search filesystems by LABEL, UUID, name and mountpoint
- How to search filesystems by type and mount options
| Category | Requirements, Conventions or Software Version Used |
|---|---|
| System | Distribution-agnostic |
| Software | findmnt |
| Other | None |
| Conventions | # – requires given linux-commands to be executed with root privileges either directly as a root user or by use of sudo command$ – requires given linux-commands to be executed as a regular non-privileged user |
Findmnt basic usage
The simplest way to use findmnt consists into invoking it without any options or arguments; in such case, the utility displays information about all mounted filesystems, organized in four columns:
- TARGET
- SOURCE
- FSTYPE
- OPTIONS
The first column, “TARGET”, holds information about the filesystem mountpoint; the second, “SOURCE”, contains the path of the source device which hosts the filesystem. The third column, “FSTYPE”, reports information about the filesystem type (e.g. ext4 or XFS); finally, the fourth column displays the mount options used for the filesystem.
Those mentioned above are the default columns used in the findmnt output. To retrieve the list of all those available, together with their brief description, we can invoke the utility with the
-H option:
$ findmnt -H
ACTION <string> action detected by --poll
AVAIL <string|number> filesystem size available, use <number> if --bytes is given
FREQ <integer> dump(8) period in days [fstab only]
FSROOT <string> filesystem root
FSTYPE <string> filesystem type
FS-OPTIONS <string> FS specific mount options
ID <integer> mount ID
INO.AVAIL <string> number of available inodes
INO.TOTAL <string> total number of inodes
INO.USED <string> number of used inodes
INO.USE% <string> percentage of INO.USED divided by INO.TOTAL
LABEL <string> filesystem label
MAJ:MIN <string> major:minor device number
OLD-OPTIONS <string> old mount options saved by --poll
OLD-TARGET <string> old mountpoint saved by --poll
OPTIONS <string> all mount options
OPT-FIELDS <string> optional mount fields
PARENT <integer> mount parent ID
PARTLABEL <string> partition label
PARTUUID <string> partition UUID
PASSNO <integer> pass number on parallel fsck(8) [fstab only]
PROPAGATION <string> VFS propagation flags
SIZE <string|number> filesystem size, use <number> if --bytes is given
SOURCE <string> source device
SOURCES <string> all possible source devices
TARGET <string> mountpoint
TID <integer> task ID
USED <string|number> filesystem size used, use <number> if --bytes is given
USE% <string> filesystem use percentage
UUID <string> filesystem UUID
VFS-OPTIONS <string> VFS specific mount options
Retrieving information about a specific filesystem
As we have already discussed, when invoked without any options or arguments, findmnt displays information about all mounted filesystems. This is seldom useful: most of the time we are interested in gathering information about a specific filesystem, which we can reference by device name, label, UUID, or by major:minor number.
The most common way to look for a filesystem, is probably by its source device:
$ findmnt /dev/mapper/vg_system-lv_root
Another option consists into passing the directory on which we know the filesytem is mounted (its mountpoint):
$ findmnt /
Findmnt is able to match the argument against both the SOURCE and TARGET columns, unless we explicitly use the
--target, --mountpoint or --source options. In the example below, the utility returns no output, since it interprets the argument as a mountpoint:
$ findmnt --mountpoint /dev/mapper/vg_system-lv_root
To reference a specific filesystem, we can also use its UUID or LABEL if we know them beforehand. Suppose we want to retrieve information about the filesystem with UUID 331392ba-8966-4877-828c-99cc4bc418ec; we would run:
$ findmnt UUID=331392ba-8966-4877-828c-99cc4bc418ec
Similarly, to reference a filesystem by its LABEL, we would run:
$ findmnt LABEL=backups
Searching in a specific file
By default, findmnt searches for filesystems in the /etc/fstab, /etc/mtab, and /proc/self/mountinfo files. Some options allow us to change this behavior. The -s (or --fstab) option, for example, makes findmnt consider only filesystems in the fstab file; similarly, the -m ( --mtab) option, restricts the search to the content of the /etc/mtab file, and -k, (short for --kernel), narrows the search to the /proc/self/mountinfo file.
We can also provide the path of a custom, alternative file, by using the -F option (short for --tab-file). To search for filesystems in the /etc/fstab-backup file, for example, we would run:
$ findmnt -F /etc/fstab-backup
Filtering results by filesystem type
In certain cases, we don’t want to target a specific filesystem, and neither to obtain the list of all mounted ones. Instead, we may want to apply a filter based on some parameter. To make findmnt return only filesystems of a certain type, for example, we can use the -t option (--type), and pass the list of types we want to use as a filter. Supposing we want to gather information about all mounted vfat or XFS filesystems, we would run:
$ findmnt -t vfat,xfs
Filtering results by mount options
Another option is to apply a filter based on mount options. To use this feature, all we have to do, is to use the -O option (short for --options) and provide the comma-separated list of options we want to use as a filter. To retrieve the list of all filesytems mounted with the “relatime” and “ro” options, for example, we would run:
$ findmount -O relatime,ro
When multiple options are specified, only filesystems mounted with all the specified options will match the query (this works like a logical AND).
Another thing to notice is that, by default, when using an option with the “no” prefix (e.g. nosuid), the expression will not match literally; instead, it will be interepted as an “exclusion” filter, and it will match all filesystems mounted without the option. Tale a look at the content of this
/etc/fstab file:
/ UUID=331392ba-8966-4877-828c-99cc4bc418ec xfs defaults,x-systemd.device-timeout=0
/boot UUID=7e28e28a-fc1b-4652-8f86-4e2bdefdad85 xfs defaults,nosuid
/boot/efi UUID=ABBE-D50B vfat defaults,uid=0,gid=0,umask=077,shortname=winnt
/home UUID=244ed50a-4223-41a5-9edb-658488d02279 xfs defaults,x-systemd.device-timeout=0
As you can see, the second filesystem in the list, the one with the 7e28e28a-fc1b-4652-8f86-4e2bdefdad85 UUID, is the only one which has “nosuid” has a mount option. Let’s run findmnt with the -O nosuid option, and let’s see what it returns:
$ findmnt --fstab -O nosuid
The output of the command above is:
TARGET SOURCE FSTYPE OPTIONS
/ UUID=331392ba-8966-4877-828c-99cc4bc418ec xfs defaults,x-systemd.device-timeout=0
/boot UUID=7e28e28a-fc1b-4652-8f86-4e2bdefdad85 xfs defaults,nosuid
/boot/efi UUID=ABBE-D50B vfat defaults,uid=0,gid=0,umask=077,shortname=winnt
/home UUID=244ed50a-4223-41a5-9edb-658488d02279 xfs defaults,x-systemd.device-timeout=0
The “query” we used, somehow unexpectedly, instead of matching only the filesystem mounted with the “nosuid” option, returned all those without the “suid” option, so all of them. If we want the expression to match literally the filesystems with the “nosuid” option, we must prefix the option with a “+”:
$ findmnt --fstab -O +nosuid
With this syntax, the expression matches the “nosuid” option literally, and yields the expected result:
TARGET SOURCE FSTYPE OPTIONS
/boot UUID=7e28e28a-fc1b-4652-8f86-4e2bdefdad85 xfs defaults,nosuid
Formatting findmnt output
A series of options allow us to modify and format the output of the findmnt command. When using findmnt in shell scripts, for example, we probably want to suppress the header row, and change the behavior of the utility so it only returns a single piece of information.
The header row can be suppressed by using the -n option (short for --noheadings), while to make the utility just return specific information, we can use the -o option (--output) and pass the comma-separated list of column(s) we are interested in, as argument. In the example below, we store the fstype of the filesystem mounted on / in the “$root_fstype” variable:
$ root_fstype="$(findmnt --noheadings --output FSTYPE /)"
$ echo "${root_fstype}"
xfs
Findmnt, by default, organizes its output in a tree-like format, which shows also the relationships between filesystems. We can change this and format the output as JSON, using the -J (--json) option. Supposing we want to reorganize the filesystem contained in the /etc/fstab file in JSON, for example, we would run:
$ findmnt -J --fstab
We would obtain a result similar to the following:
{
"filesystems": [
{
"target": "/",
"source": "UUID=331392ba-8966-4877-828c-99cc4bc418ec",
"fstype": "xfs",
"options": "defaults,x-systemd.device-timeout=0"
},{
"target": "/boot",
"source": "UUID=7e28e28a-fc1b-4652-8f86-4e2bdefdad85",
"fstype": "xfs",
"options": "defaults,nosuid"
},{
"target": "/boot/efi",
"source": "UUID=ABBE-D50B",
"fstype": "vfat",
"options": "defaults,uid=0,gid=0,umask=077,shortname=winnt"
},{
"target": "/home",
"source": "UUID=244ed50a-4223-41a5-9edb-658488d02279",
"fstype": "xfs",
"options": "defaults,x-systemd.device-timeout=0"
}
]
}
Alternatively, we can use the “list” format by passing the -l (--list) option. This format is automatically used when we apply filters to restrict a query.
Conclusions
In this tutorial, we learned to use the findmnt utility to retrieve information about mounted filesystems on Linux. The utility is installed by default in practically all the major distributions. We saw how to list all mounted filesystems, how to reference a filesystem by UUID, LABEL, name and mountpoint, and how to filter findmnt results by mount options and filesystem types.
