Also, systemd automatically mounts hierarchies for important kernel resource controllers in the
/sys/fs/cgroup/ directory.Resource controller (cgroup subsystem): Allow you set limits on each resource.
Systemd Unit Types
All processes running on the system are child processes of the systemd init process. Systemd provides three unit types that are used for the purpose of resource control
Service — A process or a group of processes, which
systemd started based on a unit configuration file. Services encapsulate the specified processes so that they can be started and stopped as one set. Scope — A group of externally created processes. Scopes encapsulate processes that are started and stopped by arbitrary processes through the
fork() function and then registered by systemd at runtime. For instance, user sessions, containers, and virtual machines are treated as scopes. Scopes are named as follows:
Slice — A group of hierarchically organized units. Slices do not contain processes, they organize a hierarchy in which scopes and services are placed. The actual processes are contained in scopes or in services. In this hierarchical tree, every name of a slice unit corresponds to the path to a location in the hierarchy. The dash ("
-") character acts as a separator of the path components. For example, if the name of a slice looks as follows:parent-name.slice
It means that a slice called parent-name.
slice is a subslice of the parent.slice. This slice can have its own sub-slice named parent-name-name2.slice, and so on.
there are four slices created by default:
-.slice — the root slice;
system.slice — the default place for all system services;
user.slice — the default place for all user sessions;
machine.slice — the default place for all virtual machines and Linux containers.
system.slice — the default place for all system services;
user.slice — the default place for all user sessions;
machine.slice — the default place for all virtual machines and Linux containers.
systemd-cgls├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
├─user.slice
│ └─user-0.slice
│ ├─session-5.scope
│ │ └─3155 /usr/sbin/anacron -s
│ ├─session-3.scope
│ │ ├─2972 sshd: root@pts/0
│ │ ├─2977 -bash
│ │ ├─3754 systemd-cgls
│ │ └─3755 systemd-cgls
│ └─session-1.scope
│ ├─1261 login -- root
│ └─2667 -bash
└─system.slice
├─crond.service
│ └─1264 /usr/sbin/crond -n
├─atd.service
│ └─1259 /usr/sbin/atd -f
├─rhnsd.service
│ └─1269 rhnsd
├─libvirtd.service
│ ├─1247 /usr/sbin/libvirtd
Important cgroup commands
systemd-cgls - Recursively show control group contents
systemd-cgtop - Show top control groups by their resource usage like CPU,Memory,Disk I/O
systemd-run - Run programs in transient scope or service or timer units
systemctl set-property - Applies limits to a CGroup
systemd-cgls
This command gives CGroup Hierarchy in a tree format.
systemd-cgtop
This show the usage of CPU, Memory ,Disk I/O of CGroups slice in the fashion of top command.
systemd-run
command is used to create and start a transient service or scope unit and run a custom command in the unit.
Following command will start a slice called aravindan.slice and a toptest.service unit will be started under this slice.
systemd-cgls - Recursively show control group contents
systemd-cgtop - Show top control groups by their resource usage like CPU,Memory,Disk I/O
systemd-run - Run programs in transient scope or service or timer units
systemctl set-property - Applies limits to a CGroup
systemd-cgls
This command gives CGroup Hierarchy in a tree format.
├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
├─user.slice
│ └─user-0.slice
│ ├─session-3.scope
│ │ ├─2972 sshd: root@pts/0
│ │ ├─2977 -bash
│ │ ├─4326 systemd-cgls
│ │ └─4327 systemd-cgls
│ └─session-1.scope
│ ├─1261 login -- root
│ └─2667 -bash
└─system.slice
├─crond.service
│ └─1264 /usr/sbin/crond -n
├─atd.service
│ └─1259 /usr/sbin/atd -f
├─rhnsd.service
│ └─1269 rhnsd
├─rhsmcertd.service
│ └─1254 /usr/bin/rhsmcertd
├─rsyslog.service
│ └─1244 /usr/sbin/rsyslogd -n
├─tuned.service
│ └─1240 /usr/bin/python -Es /usr/sbin/tuned -l -P
├─postfix.service
│ ├─1910 /usr/libexec/postfix/master -w
│ ├─1990 pickup -l -t unix -u
│ └─1991 qmgr -l -t unix -u
├─sshd.service
│ └─1451 /usr/sbin/sshd
├─cups.service
│ └─1234 /usr/sbin/cupsd -f
├─NetworkManager.service
This show the usage of CPU, Memory ,Disk I/O of CGroups slice in the fashion of top command.
Path Tasks %CPU Memory Input/s Output/s
/ 177 1.4 268.9M - -
/system.slice/ModemManager.service 1 - - - -
/system.slice/NetworkManager.service 2 - - - -
/system.slice/abrt-oops.service 1 - - - -
/system.slice/abrt-xorg.service 1 - - - -
/system.slice/abrtd.service 1 - - - -
/system.slice/alsa-state.service 1 - - - -
/system.slice/atd.service 1 - - - -
/system.slice/auditd.service 3 - - - -
/system.slice/avahi-daemon.service 2 - - - -
systemd-run
command is used to create and start a transient service or scope unit and run a custom command in the unit.
Following command will start a slice called aravindan.slice and a toptest.service unit will be started under this slice.
systemd-run --unit=name --scope --slice=slice_name command
[root@server1 ~]# systemd-run --unit=toptest --slice=aravindan.slice top -b
Running as unit toptest.service.
[root@server1 ~]# systemd-cgls /: ├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 21 ├─aravindan.slice │ └─toptest.service │ └─4717 /usr/bin/top -b ├─user.slice │ └─user-0.slice
[root@server1 ~]# systemctl status toptest
● toptest.service - /usr/bin/top -b
Loaded: loaded (/run/systemd/system/toptest.service; static; vendor preset: disabled)
Drop-In: /run/systemd/system/toptest.service.d
└─50-Description.conf, 50-ExecStart.conf, 50-Slice.conf
Active: active (running) since Sat 2019-12-21 21:45:45 IST; 4min 10s ago
Main PID: 4717 (top)
CGroup: /aravindan.slice/toptest.service
└─4717 /usr/bin/top -b
Dec 21 21:49:53 server1.example.com top[4717]: 2667 root 20 0 116648 3420 1780 S 0.0 0.2 0:00.37 bash
Dec 21 21:49:53 server1.example.com top[4717]: 2977 root 20 0 116280 3124 1796 S 0.0 0.2 0:00.76 bash
Dec 21 21:49:53 server1.example.com top[4717]: 3566 root 20 0 0 0 0 S 0.0 0.0 0:00.07 kworker/u2+
Dec 21 21:49:53 server1.example.com top[4717]: 3665 root 20 0 112820 15868 3392 S 0.0 0.8 0:00.04 dhclient
Dec 21 21:49:53 server1.example.com top[4717]: 4406 postfix 20 0 91164 3964 2968 S 0.0 0.2 0:00.04 pickup
Dec 21 21:49:53 server1.example.com top[4717]: 4494 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:+
Dec 21 21:49:53 server1.example.com top[4717]: 4535 root 0 -20 0 0 0 S 0.0 0.0 0:00.02 kworker/0:+
Dec 21 21:49:53 server1.example.com top[4717]: 4557 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0
Dec 21 21:49:53 server1.example.com top[4717]: 4596 root 20 0 487104 7060 3996 S 0.0 0.4 0:00.05 packagekitd
Dec 21 21:49:53 server1.example.com top[4717]: 4714 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kworker/0:2
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