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# numcpus
[](https://pkg.go.dev/github.com/tklauser/numcpus)
[](https://github.com/tklauser/numcpus/actions?query=workflow%3ATests)
[](https://goreportcard.com/report/github.com/tklauser/numcpus)
Package numcpus provides information about the number of CPU in a system.
It gets the number of CPUs (online, offline, present, possible, configured or
kernel maximum) on a Linux, Darwin, FreeBSD, NetBSD, OpenBSD, DragonflyBSD or
Solaris/Illumos system.
On Linux, the information is retrieved by reading the corresponding CPU
topology files in `/sys/devices/system/cpu`.
Not all functions are supported on Darwin, FreeBSD, NetBSD, OpenBSD,
DragonflyBSD and Solaris/Illumos.
## Usage
```Go
package main
import (
"fmt"
"os"
"github.com/tklauser/numcpus"
)
func main() {
online, err := numcpus.GetOnline()
if err != nil {
fmt.Fprintf(os.Stderr, "GetOnline: %v\n", err)
}
fmt.Printf("online CPUs: %v\n", online)
possible, err := numcpus.GetPossible()
if err != nil {
fmt.Fprintf(os.Stderr, "GetPossible: %v\n", err)
}
fmt.Printf("possible CPUs: %v\n", possible)
}
```
## References
* [Linux kernel sysfs documentation for CPU attributes](https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-devices-system-cpu)
* [Linux kernel CPU topology documentation](https://www.kernel.org/doc/Documentation/cputopology.txt)
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