cgroups

README

cgroups

Go package for creating, managing, inspecting, and destroying cgroups. The resources format for settings on the cgroup uses the OCI runtime-spec found here.

Examples (v1)

Create a new cgroup

This creates a new cgroup using a static path for all subsystems under /test.

• /sys/fs/cgroup/cpu/test
• /sys/fs/cgroup/memory/test
• etc....

It uses a single hierarchy and specifies cpu shares as a resource constraint and uses the v1 implementation of cgroups.

shares := uint64(100)
control, err := cgroup1.New(cgroup1.Default, cgroup1.StaticPath("/test"), &specs.LinuxResources{
    CPU: &specs.LinuxCPU{
        Shares: &shares,
    },
})
defer control.Delete()

Create with systemd slice support

control, err := cgroup1.New(cgroup1.Systemd, cgroup1.Slice("system.slice", "runc-test"), &specs.LinuxResources{
    CPU: &specs.CPU{
        Shares: &shares,
    },
})

Load an existing cgroup

control, err = cgroup1.Load(cgroup1.Default, cgroups.StaticPath("/test"))

Add a process to the cgroup

if err := control.Add(cgroup1.Process{Pid:1234}); err != nil {
}

Update the cgroup

To update the resources applied in the cgroup

shares = uint64(200)
if err := control.Update(&specs.LinuxResources{
    CPU: &specs.LinuxCPU{
        Shares: &shares,
    },
}); err != nil {
}

Freeze and Thaw the cgroup

if err := control.Freeze(); err != nil {
}
if err := control.Thaw(); err != nil {
}

List all processes in the cgroup or recursively

processes, err := control.Processes(cgroup1.Devices, recursive)

Get Stats on the cgroup

stats, err := control.Stat()

By adding cgroups.IgnoreNotExist all non-existent files will be ignored, e.g. swap memory stats without swap enabled

stats, err := control.Stat(cgroup1.IgnoreNotExist)

Move process across cgroups

This allows you to take processes from one cgroup and move them to another.

err := control.MoveTo(destination)

Create subcgroup

subCgroup, err := control.New("child", resources)

Registering for memory events

This allows you to get notified by an eventfd for v1 memory cgroups events.

event := cgroup1.MemoryThresholdEvent(50 * 1024 * 1024, false)
efd, err := control.RegisterMemoryEvent(event)

event := cgroup1.MemoryPressureEvent(cgroup1.MediumPressure, cgroup1.DefaultMode)
efd, err := control.RegisterMemoryEvent(event)

efd, err := control.OOMEventFD()
// or by using RegisterMemoryEvent
event := cgroup1.OOMEvent()
efd, err := control.RegisterMemoryEvent(event)

Examples (v2/unified)

Check that the current system is running cgroups v2

var cgroupV2 bool
if cgroups.Mode() == cgroups.Unified {
	cgroupV2 = true
}

Create a new cgroup

This creates a new systemd v2 cgroup slice. Systemd slices consider "-" a special character, so the resulting slice would be located here on disk:

• /sys/fs/cgroup/my.slice/my-cgroup.slice/my-cgroup-abc.slice

import (
    "github.com/containerd/cgroups/v2/cgroup2"
    specs "github.com/opencontainers/runtime-spec/specs-go"
)

res := cgroup2.Resources{}
// dummy PID of -1 is used for creating a "general slice" to be used as a parent cgroup.
// see https://github.com/containerd/cgroups/blob/1df78138f1e1e6ee593db155c6b369466f577651/v2/manager.go#L732-L735
m, err := cgroup2.NewSystemd("/", "my-cgroup-abc.slice", -1, &res)
if err != nil {
	return err
}

Load an existing cgroup

m, err := cgroup2.LoadSystemd("/", "my-cgroup-abc.slice")
if err != nil {
	return err
}

Delete a cgroup

m, err := cgroup2.LoadSystemd("/", "my-cgroup-abc.slice")
if err != nil {
	return err
}
err = m.DeleteSystemd()
if err != nil {
	return err
}

Attention

All static path should not include /sys/fs/cgroup/ prefix, it should start with your own cgroups name

Project details

Cgroups is a containerd sub-project, licensed under the Apache 2.0 license. As a containerd sub-project, you will find the:

• Project governance,
• Maintainers,
• and Contributing guidelines

information in our containerd/project repository.

Documentation

Index

• func RunningInUserNS() bool
• type CGMode
  • func Mode() CGMode

Functions

func RunningInUserNS

func RunningInUserNS() bool

RunningInUserNS detects whether we are currently running in a user namespace. Copied from github.com/lxc/lxd/shared/util.go

Types

type CGMode

type CGMode int

CGMode is the cgroups mode of the host system

const (
	// Unavailable cgroup mountpoint
	Unavailable CGMode = iota
	// Legacy cgroups v1
	Legacy
	// Hybrid with cgroups v1 and v2 controllers mounted
	Hybrid
	// Unified with only cgroups v2 mounted
	Unified
)

func Mode

func Mode() CGMode

Mode returns the cgroups mode running on the host