User:igo95862/cgroups
cgroups (aka control groups) is a Linux kernel feature to limit, police and account the resource usage for a set of processes. Compared to other approaches like the 'nice' command or /etc/security/limits.conf
, cgroups are more flexible as they can operate on (sub)sets of processes (possibly with different system users) and support advanced features such as limiting processes to certain CPUs. When a cgroup gets closed all of its children will get closed as well.
Systemd uses groups in multiple ways:
- Every
.service
spawns its own CGroup - Services are grouped under
.slice
and.scope
- cgroups are hierarchical, child groups can not acquire more resources than parent
Installation
Cgroups are part of and packaged with systemd.
Configuration
Information
Hierarchy
Current cgroup hierarchy can be seen with systemctl status
or systemd-cgls
command.
systemctl status
● myarchlinux State: running Jobs: 0 queued Failed: 0 units Since: Wed 2019-12-04 22:16:28 UTC; 1 day 4h ago CGroup: / ├─user.slice │ └─user-1000.slice │ ├─user@1000.service │ │ ├─gnome-shell-wayland.service │ │ │ ├─ 1129 /usr/bin/gnome-shell │ │ ├─gnome-terminal-server.service │ │ │ ├─33519 /usr/lib/gnome-terminal-server │ │ │ ├─37298 fish │ │ │ └─39239 systemctl status │ │ ├─init.scope │ │ │ ├─1066 /usr/lib/systemd/systemd --user │ │ │ └─1067 (sd-pam) │ └─session-2.scope │ ├─1053 gdm-session-worker [pam/gdm-password] │ ├─1078 /usr/bin/gnome-keyring-daemon --daemonize --login │ ├─1082 /usr/lib/gdm-wayland-session /usr/bin/gnome-session │ ├─1086 /usr/lib/gnome-session-binary │ └─3514 /usr/bin/ssh-agent -D -a /run/user/1000/keyring/.ssh ├─init.scope │ └─1 /sbin/init └─system.slice ├─systemd-udevd.service │ └─285 /usr/lib/systemd/systemd-udevd ├─systemd-journald.service │ └─272 /usr/lib/systemd/systemd-journald ├─NetworkManager.service │ └─656 /usr/bin/NetworkManager --no-daemon ├─gdm.service │ └─668 /usr/bin/gdm └─systemd-logind.service └─654 /usr/lib/systemd/systemd-logind
Find cgroup of a process
The cgroup name of a proccess can be found under /proc/PID/cgroup
.
For example, the cgroup of the shell:
cat /proc/self/cgroup
0::/user.slice/user-1000.slice/session-3.scope
cgroup resource usage
The systemd-cgtop
command can be used to see the resource usage:
systemd-cgtop
Control Group Tasks %CPU Memory Input/s Output/s user.slice 540 152,8 3.3G - - user.slice/user-1000.slice 540 152,8 3.3G - - user.slice/u…000.slice/session-1.scope 425 149,5 3.1G - - system.slice 37 - 215.6M - -
Custom CGroups
systemd.slice(5) systemd unit files can be used to define a custom cgroup configuration.
The resource control options that can be assigned are documented in systemd.resource-control(5)
Example slice unit that only allows 30% of cpu used:
[Slice] CPUQuota=30%
As service
Service unit file
Resources can be directly specified in service definition or as a Systemd#Drop-in_files
[Service] MemoryMax=1G # Limit service to 1 gigabyte
Grouping unit under a slice
Service can be specified what slice to run in:
[Service] Slice=my.slice
As root
systemd-run
can be used to run a command in a specific slice.
$ systemd-run --slice=my.slice command
--uid=username
option can be used to spawn the command as specific user.
$ systemd-run --uid=username --slice=my.slice command
--shell
option can be used to spawn a command shell inside the slice.
As unprivileged user
Unpriveleged users can divide the resources provided to them into new cgroups, if some conditions are met.
Version 1 cgroups must be disabled for a non-root user to be allowed to manage resources Cgroups.
Disabling cgroups v1
Arch Linux enables both v1 and v2 cgroups by default.
To disable v1 cgroups, the systemd.unified_cgroup_hierarchy
Kernel_parameters can be used.
Verify that v1 cgroups have been disabled:
ls /sys/fs/cgroup
cgroup.controllers cgroup.subtree_control init.scope/ system.slice/ cgroup.max.depth cgroup.threads io.cost.model user.slice/ cgroup.max.descendants cpu.pressure io.cost.qos cgroup.procs cpuset.cpus.effective io.pressure cgroup.stat cpuset.mems.effective memory.pressure
If you see something like this, you still have v1 groups enabled:
ls /sys/fs/cgroup
blkio/ cpu,cpuacct/ freezer/ net_cls@ perf_event/ systemd/ cpu@ cpuset/ hugetlb/ net_cls,net_prio/ pids/ unified/ cpuacct@ devices/ memory/ net_prio@ rdma/
Controller types
Not all resources can be controlled by user.
Controller | Can be controlled by user | Options |
---|---|---|
cpu | Requires delegation | CPUAccounting, CPUWeight, CPUQuota, AllowedCPUs, AllowedMemoryNodes |
io | Requires delegation | IOWeight, IOReadBandwidthMax, IOWriteBandwidthMax, IODeviceLatencyTargetSec |
memory | Yes | MemoryLow, MemoryHigh, MemoryMax, MemorySwapMax |
pids | Yes | TasksMax |
rdma | No | ? |
eBPF | No | IPAddressDeny, DeviceAllow, DevicePolicy |
User Delegation
For user to control cpu and io resources, the resources need to be delegated. This can be done by creating a unit overload.
For example if your user id is 1000:
systemctl edit user@1000.service
[Service] Delegate=yes
Reboot and verify that the slice your user session is under has cpu and io controller:
cat /sys/fs/cgroup/user.slice/user-1000.slice/cgroup.controllers
cpuset cpu io memory pids
User defined slices
The user slice files can be placed in ~/.config/systemd/user/
.
To run the command under certain slice:
$ systemd-run --user --slice=my.slice command
You can also run your login shell inside the slice:
$ systemd-run --user --slice=my.slice --shell
Run-time adjustment
cgroups resources can be adjusted at run-time using systemctl set-property
command. Option syntax is the same as in systemd.resource-control(5).
--runtime
option is passed. Adjustments are saved at /etc/systemd/system.control/
for system wide options and .config/systemd/user.control/
for user options.For example, cutting off internet access for all user sessions:
$ systemctl set-property user.slice IPAddressDeny=any
Examples
Matlab
Doing large calculations in MATLAB can crash your system, because Matlab does not have any protection against taking all your machine's memory or CPU. The following example shows a cgroup that constrains Matlab to first 6 CPU cores and 5 GB of memory.
~/.config/systemd/user/matlab.slice
[Slice] AllowedCPUs=0-5 MemoryHigh=6G
Launch Matlab like this (be sure to use the right path):
$ systemd-run --user --slice=matlab.slice /opt/MATLAB/2012b/bin/matlab -desktop