Linux cgroups

External

• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/resource_management_guide/ch01
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/resource_management_guide/chap-introduction_to_control_groups
• https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
• https://en.wikipedia.org/wiki/Cgroups
• http://man7.org/linux/man-pages/man7/cgroups.7.html

Internal

• Docker Concepts

Overview

cgroups is a Linux kernel feature that allows allocation of resources (CPU, system memory, network bandwidth, or a combination of these) among user-defined groups of processes running on the system. cgroups not only track groups of processes, but they also expose metrics about CPU, memory and block I/O usage.

cgroups are exposed through a pseudo-filesystem available at /sys/fs/cgroup (older systems expose it at /cgroup). The sub-directories of the cgroup pseudo-filesystem root correspond to different cgroups hierarchies: cpu, freezer, blkio.

This command returns a list of the cgroups that are mounted:

cat /proc/mounts | grep cgroup

cgroups are organized hierarchically, child cgroups inheriting certain attributes from their parent group. Many different hierarchies of cgroups can exist simultaneously on a system. Each hierarchy is attached to one or more subsystem, where a subsystem represents a single resource like CPU time or memory.

cgroups can be configured via the cgconfig service.

cgroups Subsystems

blkio

Sets limits on input/output access from and to block devices.

cpu

Uses the scheduler to provide cgroup tasks access to the CPU.

cpuacct

Generates automatic reports on CPU resources.

cpuset

Assigns individual CPUs and memory nodes to tasks in a cgroup.

net_cls

Tags network packets with a tag identifier (classid) that allow the Linux traffic controller (tc) to identify packets.

ns

The namespace subsystem.

Operations

The recommended location for cgroup hierarchies:

/sys/fs/cgroup