> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Filesystem and Mount Options
> This guide explores examining and adjusting filesystem mount options to optimize system configuration and improve performance and security.
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:
```bash theme={null}
$ findmnt
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/ubuntu--vg-ubuntu--lv ext4 rw,relatime,seclabel
├─/proc proc proc rw,nosuid,nodev,noexec,relatime
│ ├─/proc/sys/fs/binfmt_misc binfmt_misc binfmt_misc rw,nosuid,nodev,noexec,relatime
│ └─/proc/sys/fs/binfmt_misc binfmt_misc binfmt_misc rw,nosuid,nodev,noexec,relatime
└─/dev /dev/pts devpts rw,nosuid,noexec,relatime,seclabel
├─/dev/pts devpts devpts rw,nosuid,noexec,relatime,seclabel
├─/dev/shm tmpfs tmpfs rw,nosuid,nodev,seclabel,inode64
├─/dev/mqueue mqueue mqueue rw,nosuid,nodev,noexec,relatime
├─/dev/hugepages hugepages hugepages rw,relatime,seclabel,pagesize=2M
├─/dev/vda2 /dev/vda2 ext4 rw,relatime,seclabel
└─/dev/vdb1 /dev/vdb1 xfs rw,relatime,seclabel,attr2,inode64
/boot /boot ext4 rw,relatime,seclabel
/mybackups /mybackups ext4 rw,relatime,seclabel
```
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:
```bash theme={null}
$ findmnt -t xfs,ext4
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/ubuntu--vg-ubuntu--lv ext4 rw,relatime,seclabel
├─/boot /dev/vda2 ext4 rw,relatime,seclabel
└─/mybackups /dev/vdb1 xfs rw,relatime,seclabel,attr2,inode64,logbufs=8
```
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:
```bash theme={null}
$ findmnt -t xfs,ext4
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/ubuntu--vg-ubuntu--lv ext4 rw,relatime,seclabel
├─/boot /dev/vda2 ext4 rw,relatime,seclabel
└─/mybackups /dev/vdb1 xfs rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota
$ sudo touch /mybacksups/testfile2
```
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:
```bash theme={null}
$ sudo touch /mybacks/testfile2
$ sudo mount -o ro /dev/vdb2 /mnt
$ findmnt -t xfs,ext4
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/ubuntu--vg-ubuntu--lv ext4 rw,relatime,seclabel
├─/boot /dev/vda2 ext4 rw,relatime,seclabel
└─/mybackups /dev/vdb1 xfs rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota
└─/mnt /dev/vdb2 ext4 ro,relatime,seclabel
$ sudo touch /mnt/testfile
touch: cannot touch '/mnt/testfile': Read-only file system
```
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:
```bash theme={null}
$ sudo umount /mnt
$ sudo mount -o ro,noexec,nosuid /dev/vdb2 /mnt
```
After mounting, verify the options with `findmnt`:
```bash theme={null}
$ findmnt -t ext4,xfs
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/ubuntu--vg-ubuntu--lv ext4 rw,relatime,seclabel
├─/boot /dev/vda2 ext4 rw,relatime,seclabel
├─/mybackups /dev/vdb1 xfs rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota
└─/mnt /dev/vdb2 ext4 ro,nosuid,noexec,relatime,seclabel
```
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:
```bash theme={null}
$ sudo umount /mnt
$ sudo mount -o ro,noexec,nosuid /dev/vdb2 /mnt
$ findmnt -t ext4,xfs
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/ubuntu--vg-ubuntu--lv ext4 rw,relatime,seclabel
├─/boot /dev/vda2 ext4 rw,relatime,seclabel
├─/mybackups /dev/vdb1 xfs rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota
└─/mnt /dev/vdb2 ext4 ro,nosuid,noexec,relatime,seclabel
$ sudo mount -o rw,noexec,nosuid /dev/vdb2 /mnt
mount: /mnt: /dev/sdb2 already mounted on /mnt.
$ sudo mount -o remount,rw,noexec,nosuid /dev/vdb2 /mnt
```
## 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:
```bash theme={null}
$ sudo umount /dev/vdb1
$ sudo mount -o allocsize=32K /dev/vdb1 /mybackups
```
For more details on XFS-specific options, refer to the XFS manual:
```bash theme={null}
$ man xfs
```
## 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:
```bash theme={null}
$ sudo vim /etc/fstab
/dev/vdb1 /mybackups xfs defaults 0 2
```
To customize the mount options (for example, setting the filesystem to read-only with no execution), modify the entry as follows:
```bash theme={null}
$ sudo vim /etc/fstab
/dev/vdb1 /mybackups xfs ro,noexec 0 2
```
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](https://www.kernel.org/doc/html/latest/filesystems/mountoptions.html) and other related links.