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:
The system runs from the active image.
Installation updates the inactive image.
When installation finishes, the boot target switches.
On the next reboot, the updated image becomes active.
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.
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