Some usefull systemd commands

systemd.txt

#to check SysV services
chkconfig --list | more

#To check systemd service files
systemctl list-unit-files
systemctl list-units

            systemd
    ___________|___________
    |          |          |
 Service     Scope       Slice
 
 Slices donot contain any process, but provide a blue print for proceses
 A Slice may contain a service or scope
 A Service is a hierachy group of process that are started via systemd
 A Scope heirarchy of process taht can start or create process dyamically
    like VM, containers, transient proceess like user sessions
    
Slice nomenclature
-------------------
  name.slice -> name-instance.slice
  -.slice is the root slice

Differnet types of Slice
-------------------------
  -.slice : the root slice on the top of all the cgroups
  system.slice: the default place for all the system services, http, sshd
  user.slice : the default place for all user sessions. sshd some systems, graphic display manager
  machine.slice: VM and containers

key cgroup commands
--------------------
  systemd-cgls
  systemd-cgtop
  systemd-run
    - To run a  transient system service
      the slice can be run under system or user or new slice under root
                    unit name       slice          command
      systemd-run --unit=toptest --slice=sai.slice top -b
  systemctl
    systemctl set-property -> applies the limits to a cgroup
  
Apply cgroup limits to a permenant process
------------------------------------------
systemctl set-property --runtime name.service MemoryLimit=1200M