Skip to main content
In this guide, we explore how to examine and adjust filesystem mount options to optimize your system configuration. We begin with commands to inspect mounted filesystems, then move on to applying and understanding various mount options. Previously, you may have used the lsblk command to view mounted devices briefly. While this command provides a concise overview, it lacks details like filesystem types and specific mount options. For a comprehensive view of all mounted filesystems, use the findmnt command. For example, running findmnt might yield output similar to the following, showing that the /dev/vdb1 partition with the XFS filesystem is mounted in the mybackups directory:
Keep in mind that on larger systems, findmnt may produce additional output lines for virtual filesystems (like proc) that are mounted in memory.
To filter out virtual filesystems and display only real ones (such as XFS and ext4), use the -t option:
Note that findmnt only displays currently mounted filesystems; those defined on a partition but not mounted will not appear. The OPTIONS column in the output indicates how each filesystem is mounted. For example, the rw option for /dev/vdb1 means that the filesystem is mounted with read-write permissions. If it were set to ro, the filesystem would be mounted as read-only, which becomes evident when you attempt to create a file:
Changing the mount option from rw to ro will make the filesystem read-only. To mount a filesystem with specific options, use the -o switch with the mount command. For example, to remount a filesystem as read-only:
This example clearly demonstrates the effect of mount options on filesystem behavior.

​
Applying Multiple Mount Options

In addition to the basic ro (read-only) option, you can enhance security using options such as noexec and nosuid:
  • noexec: Prevents the execution of any executable files stored on the filesystem.
  • nosuid: Disables the SUID (Set User ID) bit, preventing programs from running with elevated privileges without using sudo.
These options are particularly useful on filesystems intended solely for storage (for example, on Android devices where file execution is not expected). To mount a filesystem with these combined options, execute the following commands:
After mounting, verify the options with findmnt:
If you need to modify the mount options—such as changing from read-only to read-write—you cannot simply mount again because the filesystem is already mounted. Instead, use the remount option:

​
Filesystem-Specific Options

The options we have discussed so far are generally applicable across multiple filesystem types. However, some options are filesystem-specific. For instance, XFS provides an option called allocsize which defines the buffered I/O end-of-file preallocation size during delayed allocation writeout. The allocsize value can be specified in powers-of-2 increments from the page size (typically 4 KiB) up to 1 GiB. By default, XFS uses dynamic allocation based on heuristics, and specifying a fixed allocsize disables this dynamic behavior. Before applying filesystem-dependent options, ensure that the filesystem is unmounted if necessary, then mount it with your desired option. For example:
For more details on XFS-specific options, refer to the XFS manual:

​
Automatic Mounting with /etc/fstab

So far, we have covered manual mounting techniques. These mount configurations can also be automated during system boot via the /etc/fstab file. A typical fstab entry might initially look like this:
To customize the mount options (for example, setting the filesystem to read-only with no execution), modify the entry as follows:
After saving your changes and rebooting, the system will automatically apply your specified mount options.
Always consult the relevant manual pages (e.g., man mount, man xfs, or man ext4) for a comprehensive list of options and their effects.

​
Summary

Mount options are crucial for defining how a filesystem behaves once mounted. They control access permissions, execution capabilities, and a variety of other characteristics. By properly configuring these options, you can improve both the performance and security of your system. This guide provides a foundation for understanding and applying various mount options. For ongoing system administration, refer to additional resources such as Mount Options Documentation and other related links.

Watch Video

Practice Lab