objectives: 3_operate_running_systems

###Boot systems into different targets manually

systemctl list-units --type=target --all - view full list of targets
systemctl get-default - get default run-level
systemctl isolate multi-user.target - change to multi-user (RL 3)
systemctl isolate graphical.target - switch to graphical (RL 5)
systemctl set-default graphical.target - set default to graphical

###Identify CPU/memory intensive processes, adjust with renice & kill

open up new tab
nice -n -10 yes - start basic process with a nice level of -10
top - view nice level of existing programs renice [-n] priority [-g|-p|-u] identifiers (group, pid, user)

####Renice

renice -n 5 -p 1701 - change priority to proc
renice -n 5 -g wheel - change priority by group
renice -n 5 -u johnny - change priority by user

####Start, stop and pause a process

kill (-SIGSTOP | -19) pid - suspend process to be continued later
kill (-SIGCONT | -18) pid - continue a process that was suspended
kill (-SIGTERM | -15) pid - kill a process, can be gracefully caught
kill (-SIGKILL | -9) pid - kill a process, cannot be caught

####Start, stop and check status of network services

systemctl status name.service - check status
- same format for service: start, stop, restart, reload, enable
systemctl enable name.service - enable service at boot