How to Use the findmnt Command in Linux to Inspect Filesystem Trees and Mount Options

Traditional Linux tools like mount or reading /proc/mounts directly output dense, unformatted walls of text that make it difficult to determine mount hierarchies, nested bind mounts, or inherited flags. Part of the core util-linux package, findmnt provides a modern, structured alternative. It displays active mount points in an intuitive visual tree, searches for filesystems by device UUID or label, verifies kernel mount options, and detects discrepancies between active mounts and static configuration files like /etc/fstab.

Viewing the Active Filesystem Hierarchy as a Tree

Executing findmnt without flags outputs a hierarchical tree representation of all mounted filesystems:

findmnt

The visual tree displays four core attributes:

• TARGET: The filesystem mount point directory (e.g., /, /boot/efi, or /var/log).
• SOURCE: The backing block device, virtual filesystem, or network export (e.g., /dev/nvme0n1p2, tmpfs, or overlay).
• FSTYPE: The filesystem format (e.g., ext4, btrfs, xfs, vfat, or nfs4).
• OPTIONS: Active runtime mount flags applied by the kernel (e.g., rw,relatime,discard).

Filtering by Block Device, Directory, or Mount Point

To inspect the mount status of a specific block device or partition:

findmnt /dev/sda1

To locate which filesystem and partition hosts a specific file or folder path:

findmnt -T /var/log/syslog

The -T (or --target) flag resolves symlinks and parent directory paths, displaying the exact mounted block volume where the file resides.

Auditing and Validating /etc/fstab Configurations

Before rebooting a server after modifying storage mounts, verify that /etc/fstab is syntactically sound and check whether static definitions match live mounts:

findmnt --verify

The --verify mode parses /etc/fstab and checks for missing source devices, invalid UUID strings, non-existent mount target directories, and unsupported filesystem options, alerting you to potential boot failures before they occur.

To display only the filesystems defined statically in /etc/fstab (regardless of whether they are currently mounted):

findmnt --fstab

Filtering by Filesystem Type and Mount Options

System administrators managing complex storage tiers can isolate filesystems based on their driver type using the -t switch:

findmnt -t ext4,btrfs,xfs

To search for filesystems mounted with specific security flags—such as locating all partitions mounted in read-only (ro) mode or identifying partitions missing noexec or nosuid protections:

findmnt -O ro
findmnt -O noexec

Generating Machine-Readable JSON and Scriptable Lists

While the tree view is ideal for human readability in the terminal, automated monitoring scripts and provisioning pipelines require tabular or structured data.

To output a flat list without tree formatting characters:

findmnt -l

To export active mount parameters formatted as structured JSON for ingestion into Python or monitoring daemons:

findmnt -J

You can also define custom column outputs using the -o parameter:

findmnt -o TARGET,SOURCE,FSTYPE,USED,AVAIL,USE%

Monitoring Live Mount and Unmount Events

Similar to dmesg -w, findmnt can monitor the kernel for real-time filesystem changes. To observe storage devices, USB drives, or network shares being attached or detached in real time:

findmnt --poll

The command blocks and streams timestamped mount, umount, and move events as they take place.

Essential findmnt Command Options Reference

Command Switch	Operational Behavior
findmnt	Visualises complete hierarchical filesystem tree.
findmnt -T [Path]	Identifies the mount point hosting a given file or directory.
findmnt --verify	Audits /etc/fstab for syntax errors, missing devices, or invalid paths.
findmnt -t [Types]	Filters output by specific filesystem formats (e.g., ext4, xfs).
findmnt -O [Option]	Filters mounts matching specific flags (e.g., ro, rw, noexec).
findmnt -J	Exports complete mount tree in computer-readable JSON format.
findmnt --poll	Streams real-time mount and unmount kernel events to stdout.