Storage and filesystem

Understand the VOS3 partition layout, application users, home directories, and runtime data model.

VOS3 uses read-only executable content, controlled read-write areas, and an A/B-aware system layout.

Use this page to understand partitions, application users, home directories, and filesystem access patterns.

File system partitions

A/B update concept

The A/B update model supports seamless updates by maintaining two system images.

• image A — active image
• image B — installation image

Images can share a single filesystem partition where needed.

The update flow is:

1. The system runs from the active image.
2. Installation updates the inactive image.
3. When installation finishes, the boot target switches.
4. On the next reboot, the updated image becomes active.
5. The next installation uses the other image.

System partitions and file system layout

The system flash memory is partitioned as follows.

Partition	Contents	Access	Notes
aboot, abootbak	Boot loader	Read-only
kernelfs_a, kernelfs_b	Linux kernel and startup system	Read-only
rootfs	System libraries, system applications, system resources, user application binaries, and read-only user resources	Read-only
sysdata	System configuration A/B, system runtime data, and system logs	Read/Write	Managed by the system
appdata	Application configuration A/B, application logs, application runtime data, and the download area	Read/Write
persist	Warrantied keys, keystore, and certstore	Read/Write	Managed by the system and kept across updates
devinfo	Device information and device mode token	Read-only	Managed by the system

Application users and home directories

Application and system users

As on earlier platforms, applications run under predefined users named usr<X>, where <X> is typically 1 to 16.

Applications run with the privileges of their assigned user and use that user's home directory.

Application users are created automatically when user-signed packages are installed.

The platform also uses predefined system and root users.

User	Notes
usr<X> (1–16)	MAC user applications, libraries, and RO resources
sys_<...>	System daemons, libraries, and applications
root	Root user

User home directories

Each application user gets a home directory with this structure.

Path	Type	Partition	Location	Permissions	Notes	A/B support
~/	dir	rootfs	/home/usr<X>	read-only	user home folder	Y
~/versioned_data	symlink	appdata	/mnt/appdata/versioned/usr<X>	read/write	versioned application data	Y
~/flash	symlink	appdata	/mnt/appdata/data/usr<X>	read/write	persistent application data	N
~/logs	symlink	appdata	/mnt/appdata/logs/usr<X>	read/write	application logs	N

Application permissions and capabilities

Applications have a limited default permission set.

A predefined set of Linux capabilities covers common application needs.

Other protected resources are accessed through system services.