This page describes a subset of the Linux kernel interfaces on which Android relies to function properly. The presence and correctness of these interfaces are tested as part of the Vendor Test Suite (VTS). This subset will grow over time to contain a larger portion of Android kernel interfaces.
System calls
All system calls are expected to provide the same signatures and semantics as in the upstream Linux kernel of the same version.
prctl
In addition to the upstream prctl operations for supported
kernel versions, Android relies on additional prctl operations, the
implementation of which can be found in the android-common kernel.
PR_SET_TIMERSLACK_PID PR_SET_VMA
File systems
The Linux kernel exports interfaces via several file systems. Android expects these interfaces to communicate the same information, in the same format, and provide the same semantics as in the upstream Linux kernel. For interfaces that do not exist upstream, the appropriate behavior is dictated by the corresponding branch of the Android common kernel.
procfs
| Interface | Description |
|---|---|
| /proc/asound/ | Read-only file showing the list of currently configured ALSA drivers. |
| /proc/cmdline | Read-only file containing command line arguments passed to the kernel. |
| /proc/config.gz | Read-only file containing kernel build configuration. |
| /proc/cpuinfo | Read-only file containing architecture-specific CPU details. |
| /proc/diskstats | Read-only file showing I/O statistics of block devices. |
| /proc/filesystems | Read-only file listing file systems currently supported by the kernel. |
| /proc/kmsg | Read-only file showing kernel messages in real time. |
| /proc/loadavg | Read-only file showing CPU and IO load average over time. |
| /proc/meminfo | Read-only file showing memory subsystem details. |
| /proc/misc | Read-only file listing miscellaneous drivers registered on the miscellaneous major device. |
| /proc/modules | Read-only file containing information about loaded kernel modules. |
| /proc/mounts | Symlink to /proc/self/mounts, which is a read-only file
listing information about the mounted file systems. |
| /proc/net | Directory containing a variety of network stack parameters. |
| /proc/net/xt_qtaguid/ | Read-write file providing information about tagged sockets. |
| /proc/pagetypeinfo | Read-only file containing page allocator information. |
| /proc/stat | Read-only file containing various kernel and system statistics. |
| /proc/swaps | Read-only file showing swap space utilization. This file is optional; its contents and permissions are verified in VTS only if the file is present. |
| /proc/sys/abi/swp | Read-write file which determines the behavior of the obsoleted ARM instruction SWP. |
| /proc/sys/fs/pipe-max-size | Read-write file that reports the maximum size, in bytes, of an individual pipe buffer. |
| /proc/sys/fs/protected_hardlinks | Read-write file that controls the behavior of creation of hard links. |
| /proc/sys/fs/protected_symlinks | Read-write file that controls the behavior of creation of symbolic links. |
| /proc/sys/fs/suid_dumpable | Read-write file that controls the core dump mode for setuid or otherwise protected/tainted binaries. |
| /proc/sys/kernel/core_pattern | Read-write file that specifies the core dump filename pattern. |
| /proc/sys/kernel/core_pipe_limit | Read-write file that defines how many concurrent crashing processes may be piped to user apps in parallel. |
| /proc/sys/kernel/dmesg_restrict | Read-write file that controls whether unprivileged users may access dmesg. |
| /proc/sys/kernel/domainname | Read-write file that contains the YP/NIS domain name of the system. |
| /proc/sys/kernel/hostname | Read-write file that determines the host name of the system. |
| /proc/sys/kernel/hung_task_timeout_secs | Read-write file that controls the timeout used to determine when a task has become non-responsive and should be considered hung. This file is optional; its contents and permissions are verified in VTS only if the file is present. |
| /proc/sys/kernel/kptr_restrict | Read-write file that determines whether kernel pointers are printed in
proc files and other interfaces. |
| /proc/sys/kernel/modules_disabled | Read-write file that controls whether kernel modules may be loaded. |
| /proc/sys/kernel/panic_on_oops | Read-write file that controls the kernel's behavior on oops. |
| /proc/sys/kernel/perf_event_max_sample_rate | Read-write file that controls the maximum sample rate of performance events. |
| /proc/sys/kernel/perf_event_paranoid | Read-write file that controls the usage of the performance events system by unprivileged users. |
| /proc/sys/kernel/pid_max | Read-write file that contains the PID allocation wrap value. |
| /proc/sys/kernel/random/boot_id | Read-only file that contains a new random ID on each boot. |
| /proc/sys/kernel/randomize_va_space | Read-write file that determines the address layout randomization policy for the system. |
| /proc/sys/kernel/sched_child_runs_first | Read-write file that controls whether newly forked tasks are favored in scheduling over their parent tasks. |
| /proc/sys/kernel/sched_latency_ns | Read-write file that contains the maximum latency, in nanoseconds, a task may incur prior to being scheduled. |
| /proc/sys/kernel/sched_rt_period_us | Read-write file that contains the period length used by the system-wide RT execution limit in microseconds. |
| /proc/sys/kernel/sched_rt_runtime_us | Read-write file that contains the amount of time, relative to sched_rt_period_us, that the system may execute RT tasks. |
| /proc/sys/kernel/sched_tunable_scaling | Read-write file that controls whether sched_latency_ns should be automatically adjusted by the scheduler based on the number of CPUs. |
| /proc/sys/kernel/sched_wakeup_granularity_ns | Read-write file that contains how much more virtual runtime task A must have than task B in nanoseconds for task B to preempt it. |
| /proc/sys/kernel/sysrq | Read-write file that controls the functions allowed to be invoked via the sysrq key. |
| /proc/sys/net/* | Directory containing a variety of network stack parameters. |
| /proc/sysrq-trigger | Write-only file that can be used to initiate sysrq functions. |
| /proc/sys/vm/dirty_background_ratio | Read-write file that contains, as a percentage of total available memory (free pages and reclaimable pages), the number of pages at which the background kernel flusher threads start writing out dirty data. |
| /proc/sys/vm/dirty_expire_centisecs | Read-write file that defines when dirty data is old enough to be eligible for write out by the kernel flusher threads. |
| /proc/sys/vm/drop_caches | Read-write file that can be used to force the kernel to drop clean caches. |
| /proc/sys/vm/extra_free_kbytes | Read-write file that can be used to keep extra free memory between the threshold where background reclaim (kswapd) kicks in, and the threshold where direct reclaim (by allocating processes) kicks in. This file is optional; its contents and permissions are verified in VTS only if the file is present. |
| /proc/sys/vm/max_map_count | Read-write file that contains the maximum number of memory map areas a process may have. |
| /proc/sys/vm/mmap_min_addr | Read-write file that determines the minimum address than can be
mmap'd. |
| /proc/sys/vm/mmap_rnd_bits | Read-write file that specifies the amount of randomness in
mmap'd addresses. |
| /proc/sys/vm/mmap_rnd_compat_bits | Read-write file that specifies the amount of randomness in
mmap'd addresses. |
| /proc/sys/vm/overcommit_memory | Read-write file that determines the kernel virtual memory accounting mode. |
| /proc/sys/vm/page-cluster | Read-write file that controls the number of pages up to which consecutive pages are read in from swap in a single attempt. |
| /proc/uid_cputime/remove_uid_range | Write-only file that, when written, removes UIDs from being shown in
/proc/uid_cputime/show_uid_stat. |
| /proc/uid_cputime/show_uid_stat | Read-only file containing the time a UID's processes spent in user and kernel space. |
| /proc/uid_io/stats | Read-only file containing a list of I/O stats for each UID in the system |
| /proc/uid_procstat/set | Write-only file used to configure a UID as foreground or background. |
| /proc/uid_time_in_state | Read-only file containing the time each UID's processes spend executing at each available frequency. This file is optional; its contents and permissions are verified in VTS only if the file is present. |
| /proc/uptime | Read-only file that shows how long the system has been running. |
| /proc/version | Read-only file containing a string describing the kernel version. |
| /proc/vmallocinfo | Read-only file containing vmalloc'd ranges. |
| /proc/vmstat | Read-only file containing virtual memory statistics from the kernel. |
| /proc/zoneinfo | Read-only file containing information about memory zones. |
dev
| Interface | Description |
|---|---|
| /dev/ashmem | Anonymous shared memory device file. |
| /dev/binder | Binder device file. |
| /dev/hwbinder | Hardware binder device file. |
| /dev/tun | Universal TUN/TAP device file. |
| /dev/xt_qtaguid | QTAGUID netfilter device file. |
sysfs
| Interface | Description |
|---|---|
| /sys/class/net/*/mtu | Read-write file containing the maximum transmission unit for each interface. |
| /sys/class/rtc/*/hctosys | Read-only file showing whether a particular rtc supplies the system time on boot and resume. |
| /sys/devices/system/cpu/ | Directory containing information about CPU configuration and frequency. |
| /sys/kernel/wakeup_reasons | Directory of read-only files containing the last suspend time and resume reason. |
| /sys/power/state | Read-write file that controls the system sleep states. |
| /sys/power/wake_lock | Read-write file that contains the active wake locks. |
| /sys/power/wake_unlock | Read-write file that contains non-active wake locks. |
| /sys/power/wakeup_count | Read-write file that can be used to put the system into a sleep state while taking into account the concurrent arrival of wakeup events. |
selinuxfs
The framework mounts selinuxfs at /sys/fs/selinux.
| Path | Description |
|---|---|
| /sys/fs/selinux/checkreqprot | Read/write file containing a binary flag that determines how selinux
protections are checked on mmap and mprotect calls.
|
| /sys/fs/selinux/null | Read/write null device for use by selinux. |
| /sys/fs/selinux/policy | Read-only file containing the selinux policy in binary form. |