Frequently Asked Questions

What is the intended use of the API?

Users should create a new instance of SystemInfo and use the getters from this class to access the platform-specific hardware and software interfaces using the respective get*() methods. The interfaces in oshi.hardware and oshi.software.os provide cross-platform functionality. See the main() method of SystemInfoTest for sample code.

Methods return a “snapshot” of current levels. To display values which change over time, it is intended that users poll for information no more frequently than approximately every second. Disk and file system calls may incur some latency and should be polled less frequently. CPU usage calculation precision depends on the relation of the polling interval to both system clock tick granularity and the number of logical processors.

Is the API backwards compatible between versions?

The interfaces and classes in oshi.hardware and oshi.software.os are considered the OSHI API and are guaranteed to be compatible with the same major version. Differences between major versions can be found in the Upgrading.md document.

Most, if not all, of the platform-specific implementations of these APIs in lower level packages will remain the same, although it is not intended that users access platform-specific code, and some changes may occur between minor versions, most often in the number of arguments passed to constructors or platform-specific methods. Supporting code in the oshi.driver and oshi.util packages may, rarely, change between minor versions, usually associated with organizing package structure or changing parsing methods for efficiency/consistency/ease of use.

Code in the platform-specific oshi.jna.* packages is intended to be temporary and will be removed when that respective code is included in the JNA project.

Does OSHI support Open Service Gateway initiative (OSGi) modules?

OSHI adds OSGi manifest entries using maven-source-plugin and mvn-bnd-plugin. Submit an issue if the configuration of these plugins needs to be adjusted to support your project.

Does OSHI support Java Module System (JPMS) modules?

OSHI publishes an oshi-core-java11 artifact with a full module descriptor (and only modular dependencies), which will allow the existing API to be placed on the module path. This artifact shares the same API as oshi-core.

The oshi-core artifact includes Automatic-Module-Name of com.github.oshi in its manifest. However, Java Module System users are encouraged to use the oshi-core-java11 artifact to take full advantage of modularization.

More fine grained modularization is being considered in a possible future major API rewrite targeting JDK 21 compatibility and leveraging features from Project Panama (JEP-370, JEP-383, and JEP-389). If you have a specific use case that would benefit from modularization, submit an issue to discuss it.

Is OSHI Thread Safe?

OSHI 5.X and above is thread safe with the exceptions noted below. @Immutable, @ThreadSafe, and @NotThreadSafe document each class. The following classes are not thread-safe:

• GlobalConfig does not protect against multiple threads manipulating the configuration programmatically. However, these methods are intended to be used by a single thread at startup in lieu of reading a configuration file. OSHI gives no guarantees on re-reading changed configurations.
• On non-Windows platforms, the getSessions() method on the OperatingSystem interface uses native code which is not thread safe. While OSHI's methods employ synchronization to coordinate access from its own threads, users are cautioned that other operating system code may access the same underlying data structures and produce unexpected results, particularly on servers with frequent new logins. The oshi.os.unix.whoCommand property may be set to parse the Posix-standard who command in preference to the native implementation, which may use reentrant code on some platforms.
• The PerfCounterQueryHandler class is not thread-safe but is only internally used in single-thread contexts, and is not intended for user use.

Earlier versions do not guarantee thread safety, and it should not be assumed.

What minimum Java version is required?

OSHI 4.x and later require minimum Java 8 compatibility. This minimum level will be retained through at least OpenJDK 8 EOL.

OSHI 3.x is compatible with Java 7 up to 3.13.x versions. OSHI 3.14.0 restored Java 6 compatibility for the oshi-core artifact only. While no new features are envisioned for this branch, bug fixes will be considered if requested on a case basis, particularly if fixed in a later version.

Which operating systems are supported?

OSHI has been implemented and tested on the following systems. Some features may work on earlier versions.

• Windows 7 and higher. (Nearly all features work on Vista and most work on Windows XP.)
• macOS version 10.6 (Snow Leopard) and higher.
• Linux (Most major distributions) Kernel 2.6 and higher
• FreeBSD 10
• OpenBSD 6.8
• Solaris 11 (SunOS 5.11)
• AIX 7.1 (POWER4)
• Android 7.0 and higher

How do I resolve Pdh call failed with error code 0xC0000BB8 issues?

OSHI (and many other programs) rely on the English Performance Counter indices in the registry. These are located at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Perflib\009\Counter. Sometimes when configuring localized Windows installations, these values become corrupt or are missing.

If you receive this PDH error code, investigate whether your English (page 009) performance counters are corrupt. Rebuild them if necessary.

How do I resolve JNA NoClassDefFoundError or NoSuchMethodError issues?

OSHI uses the latest version of JNA, which may conflict with other dependencies your project (or its parent) includes. If you experience a NoClassDefFoundError or NoSuchMethodError issues with JNA artifacts, likely causes include file system permissions or an older version of either jna or jna-platform in your classpath from a transitive dependency on another project. Consider one or more of the following steps to resolve the conflict:

• JNA needs to write its native DLL, usually to a temporary file unless you've configured otherwise. File system permissions or capacity may prevent this from happening. Pre-extracting the DLL and placing it in a known location resolves this.
• Use a dependency analyzer to verify you're importing the correct version.
• If using Maven, import OSHI's dependency management per Maven Documentation
• If using Maven, list OSHI earlier (or first) in your dependency list to influence dependency resolution.
• Specify the most recent version of JNA (both jna and jna-platform artifacts) in your pom.xml (For Gradle, build.gradle includes additional options to force the version). For Android, see the next paragraph.
• If you are using the Spring Boot Starter Parent version 2.2 and earlier that includes JNA as a dependency:
  • Upgrade to version 2.3 which does not have a JNA dependency (preferred)
  • If you must use version 2.2 or earlier, override the jna.version property to the latest JNA version.

For Android, see the JNA FAQ for additional requirements relating to Android and ProGuard, specifically:

• Use the AAR artifact dependency rather than the JAR (for jna dependency only):
  • In Gradle (build.gradle), you'll need to add @aar after the version
  • In Maven (pom.xml), you'll need to specify <type>aar</type>
  • In both cases you should add an exclusion to your oshi-core dependency for the (default) jna JAR artifact.
• In ProGuard, use -keep directives to prevent obfuscating JNA classes

Why does OSHI's System and Processor CPU usage differ from the Windows Task Manager?

CPU usage is generally calculated as (active time / active+idle time).

For System and per-Processor CPU ticks calculations, the total number of “idle” ticks is available for this calculation, which matches operating system displays on Windows 7 and earlier, and Unix-based operating systems, and CPU usage will never exceed 100%.

Starting with Windows 8, a change was made to the way that Task Manager and Performance Monitor report CPU utilization. The values in Task Manager now correspond to the Processor Information\% Processor Utility and Processor Information\% Privileged Utility performance counters, not to the Processor Information\% Processor Time and Processor Information\% Privileged Time counters as in Windows 7.

This fundamentally changes the Task Manager's meaning of “CPU Usage”. Windows documentation for % Processor Time states:

% Processor Time is the percentage of elapsed time that the processor spends to execute a non-Idle thread… This counter is the primary indicator of processor activity, and displays the average percentage of busy time observed during the sample interval.

The documentation for % Processor Utility now used by the Task Manager displays a different metric:

Processor Utility is the amount of work a processor is completing, as a percentage of the amount of work the processor could complete if it were running at its nominal performance and never idle. On some processors, Processor Utility may exceed 100%.

Features which change CPU frequency such as Intel Speed Step, Intel Turbo Boost, AMD Precision Boost, and others, can cause this value to exceed 100% on both individual processors and the entire system. While a “work completed” metric has some benefits as a performance measure, the Task Manager caps the value at 100%, which means the Task Manager shows “the amount of work a processor is completing compared to its nominal performance, except if it's over 100% we won't tell you how much extra work it's doing.”

If you desire OSHI's output to match the Task Manager, you may optionally enable this setting in the configuration file, or by calling GlobalConfig.set(GlobalConfig.OSHI_OS_WINDOWS_CPU_UTILITY, true); shortly after startup (at least before the first instantiation of the Central Processor class). Note that OSHI will not cap its CPU Usage calculation at 100%, giving you more information than the Windows Task Manager if the “work completed” metric is important to you.

For this calculation to produce meaningful data, the ticks used to calculate usage must have come from the same instance of CentralProcessor. Also, the first polling interval must be less than 7 minutes to properly initialize values.

Why does OSHI's Process CPU usage differ from the Windows Task Manager?

CPU usage is generally calculated as (active time / active+idle time). On a multi-processor system, the “idle” time can be accrued on each/any of the logical processors.

For per-Process CPU ticks, there is no “idle” counter available, so the calculation ends up being (active time / up time). It is possible for a multi-threaded process to accrue more active clock time than elapsed clock time, and result in CPU usage over 100% (e.g., on a 4-processor system it could in theory reach 400%). This interpretation matches the value displayed in ps or top on Unix-based operating systems. However, Windows scales process CPU usage to the system, so that the sum of all Process CPU percentages can never exceed 100% (ignoring roundoff errors). On a 4-processor system, a single-threaded process maximizing usage of one logical processor will show (on Windows) as 25% usage. OSHI's calculation for Process CPU load will report the Unix-based calculation in this class, which would be closer to 100%.

If you want per-Process CPU load to match the Windows Task Manager display, you should divide OSHI's calculation by the number of logical processors. This is an entirely cosmetic preference.

Why does OSHI freeze for 20 seconds (or larger multiples of 20 seconds) on Windows when it first starts up?

The initial call to some Windows Management Instrumentation (WMI) queries sometimes trigger RPC-related negotiation delays and timeouts described here. OSHI attempts to use performance counters in preference to WMI whenever possible, but includes the WMI queries as a backup. There are several potential causes of these delays, which seem to occur more often on corporate-managed machines. If you are experiencing these delays, you can configure RPC and shorten the timeout by altering registry values under HKLM\SYSTEM\CurrentControlSet\Control. The SCMApiConnectionParam value (defaults to 21000 ms) can be reduced to shorten the delay.

How is OSHI different from SIGAR?

Both OSHI and Hyperic's SIGAR (System Information Gatherer and Reporter) provide cross-platform operating system and hardware information, and are both used to support distributed system monitoring and reporting, among other use cases. The OSHI project was started, and development continues, to overcome specific shortcomings in SIGAR for some use cases. OSHI does have feature parity with nearly all SIGAR functions. Key differences include:

• Additional DLL SIGAR's implementation is primarily in native C, compiled separately for its supported operating systems. It therefore requires users to download an additional DLL specific to their operating system. This does have a few advantages for specific, targeted use cases, including faster native code routines, and availability of some native compiler intrinsics. In contrast, OSHI accesses native APIs using JNA, which does not require user installation of any additional platform-specific DLLs.
• Corporate Development / Abandonment SIGAR was developed commercially at Hyperic to support monitoring of their HQ product. Hyperic's products were later acquired by VMWare, which has transitioned away from Hyperic products and have completely abandoned SIGAR. The last release was in 2010 and the last source commit was in 2015. Multiple independent forks by existing users attempt to fix specific bugs/incompatibilities but none has emerged as a maintained/released fork. In contrast, OSHI's development has been entirely done by open source volunteers, and it is under active development as of 2021.
• Support SIGAR is completely unsupported by its authors, and there is no organized community support. OSHI is supported actively to fix bugs, respond to questions, and implement new features.

Does OSHI work on …

Will you implement … ?

Maybe! If you can contribute all the code to implement the feature, it will almost certainly be added. Even if you can't code but can provide pointers to where the information can be found cross-platform, your feature has a good chance. Otherwise, you can always submit an issue to ask, but are at the mercy of the developers' time, enthusiasm level, and the availability of documentation for the feature.