In Ubuntu, the default file system used for most installations is ext4 (the fourth extended filesystem). It is a widely used and highly stable file system, designed for Linux, and is the standard choice for many Linux distributions, including Ubuntu.

Here are some other file systems you can use in Ubuntu:

1. ext4:
   • Default in Ubuntu.
   • Features journaling, large file support, and extended attributes.
   • Suitable for most desktop and server use cases.
2. ZFS:
   • A robust file system with advanced features like snapshots, data integrity, and replication.
   • Supported natively in Ubuntu, but you need to install the zfsutils-linux package to enable it.
   • Commonly used for high-reliability systems, like servers or data storage solutions.
3. XFS:
   • High-performance file system often used for large-scale data storage.
   • Particularly good for managing large files and scalable environments.
   • You can choose XFS during installation or format a disk to XFS afterward.
4. Btrfs:
   • A modern file system with features like snapshots, compression, and subvolumes.
   • Designed for better scalability and data integrity.
   • Not as commonly used as ext4 but an option for users looking for advanced features.
5. ext3:
   • An older version of ext4.
   • Still supported, but generally not used anymore unless for compatibility reasons.
6. FAT32/exFAT/NTFS:
   • Used for compatibility with Windows systems.
   • FAT32 and exFAT are often used for USB drives and external storage.
   • NTFS is commonly used when sharing disks with Windows, and Ubuntu supports it via the ntfs-3g package.

During the Ubuntu installation process, you can choose the file system you want to use for your partitions. For most users, ext4 remains the best option unless there’s a specific requirement for a different file system.