ext4 : mount options for ext4 file system in /etc/fstab

In /etc/fstab, usually the mount option is mentioned as defaults, like follows


UUID=fffff7aa-57b8-40aa-baa4-588c4eff7651          /              ext4    defaults        1 1
UUID=8b5a0a93-1dd3-4394-bb3e-0032a77201fa     /boot       ext4    defaults        1 2

What does this option defaults stand for in ext4 file system?

The default options for ext4 file system are: rw, suid, dev, exec, auto, nouser, async

Different file system mount options available are

auto       - Mount automatically at boot, or when the command mount -a is issued.

noauto   - Mount only when you tell it to.

exec      - Allow execution of binaries on the filesystem.

noexec  - Disallow execution of binaries on the filesystem.

ro         - Mount the filesystem read-only.

rw        - Mount the filesystem read-write.

user      - Allow any user to mount the filesystem. This automatically implies noexec, nosuid, nodev, unless overridden.

users    - Allow any user in the users group to mount the filesystem.

nouser  - Allow only root to mount the filesystem.

owner  - Allow the owner of device to mount.

sync     - I/O should be done synchronously.

async   - I/O should be done asynchronously.

dev      - Interpret block special devices on the filesystem.

nodev  - Don't interpret block special devices on the filesystem.

suid    - Allow the operation of suid, and sgid bits. They are mostly used to allow users on a computer system to execute binary executables with temporarily elevated privileges in order to perform a specific task.

nosuid - Block the operation of suid, and sgid bits.

noatime     - Don't update inode access times on the filesystem. Can help performance

nodiratime - Do not update directory inode access times on the filesystem. Can help performance 

relatime     - Update inode access times relative to modify or change time. Access time is only updated if the previous access time was earlier than the current modify or change time. Similar to noatime. Can help performance.

flush        - The vfat option to flush data more often, thus making copy dialogs or progress bars to stay up until all data is written  

acl         - Enable Access Control List(acl) for filesystem