Pocesses and task scheduling

Question 1

customize ps columns

Answer 1

ps -o comm,pid,ppid,user

Question 2

show processes for a specific command

Answer 2

ps -C sshd

Question 3

find pid of a specific process

Answer 3

pidof rsyslogd
pgrep rsyslogd

Question 4

list processes by user or group

Answer 4

ps -u user1
ps -G root

Question 5

explain niceness

Answer 5

the priority given to a process, -20 = highest priority, 19 = lowest priority, default is 0

Question 6

list process with niceness column

Answer 6

ps -efl = lower case L
NI column is niceness

Question 7

run a program with different niceness value

Answer 7

nice -n -10 top
or
nice -n 2 top

Question 8

alter process priority will process running

Answer 8

sudo renice -n -5 $(pidof top)

Question 9

list kill signals

Answer 9

kill -l

Question 10

default kill signal number

Answer 10

15 - soft kill - terminate in an orderly fashion

Question 11

kill crond with kill and pkill

Answer 11

sudo pkill crond
sudo kill $(pidof crond)

pkill uses the name as kill need PID

Question 12

kill all crond processes

Answer 12

killall crond

Question 13

force kill crond

Answer 13

kill -9 $(pidof crond)
pkill -9 crond

Question 14

where are submitted at jobs stored

Answer 14

var/spool/at

Question 15

submit an at job

Answer 15

at 11:30pm 3/31/22
at>date &> /tmp/date.out
at>press ctrl d

Question 16

list at jobs

Answer 16

atq

Question 17

where are system crontables stored

Answer 17

/etc/crontab
/etc/cron.d

Question 18

where are submitted cron jobs stored for user1

Answer 18

/var/spool/cron/user1

Question 19

crontable syntax

Answer 19

Field1 - minute of hour
Field2 - hour of day
Field3 - Day of month
Field4 - Month of year
Field5 - day of week
Field6 - Command or program to execute

*/5 10-11 5,20 * * echo “Hello” > /tmp/hello.out

https://www.adminschoice.com/crontab-quick-reference
https://crontab.guru/

Question 20

Where do the scheduling daemons store log information of executed jobs?

Answer 20

The scheduling daemons store log information of executed jobs in the
/var/log/cron file.