Processes and Job Control

Question 1

What command should we use to display current running processes?

Answer 1

ps

root@CentOS # ps -ef | tail -10
ec2-user    3750    3736  0 14:40 ?        00:00:00 sshd: ec2-user@pts/0
ec2-user    3751    3750  0 14:40 pts/0    00:00:00 -bash
root        3774       2  0 14:45 ?        00:00:00 [kworker/u30:0-events_unbound]
root        3775       2  0 14:45 ?        00:00:00 [kworker/0:0-events]
root        3779    3751  0 14:48 pts/0    00:00:00 sudo su -
root        3781    3779  0 14:48 pts/0    00:00:00 su -
root        3782    3781  0 14:48 pts/0    00:00:00 -bash
root        3806       2  0 14:52 ?        00:00:00 [kworker/0:1-events]
root        3817    3782  0 14:56 pts/0    00:00:00 ps -ef
root        3818    3782  0 14:56 pts/0    00:00:00 tail -10

-e = for all process from all user
-f = for details with all column

Question 2

How can we see all the processes (not only the ones for the current session) with ps?

Answer 2

ps -ef

Question 3

What command should we use for seeing the processes in a tree like view?

Answer 3

pstree

root@CentOS # pstree
systemd─┬─NetworkManager───2*[{NetworkManager}]
        ├─2*[agetty]
        ├─auditd───{auditd}
        ├─chronyd
        ├─crond
        ├─dbus-broker-lau───dbus-broker
        ├─rngd
        ├─rsyslogd───2*[{rsyslogd}]
        ├─sshd───sshd───sshd───bash───sudo───su───bash───pstree
        ├─systemd───(sd-pam)
        ├─systemd-journal
        ├─systemd-logind
        └─systemd-udevd

Question 4

What command should we use for an interactive process viewer?

Answer 4

top or htop (htop is not present in some Linux Systems)

Question 5

Which command should we use to run a command in the background?

Answer 5

command &

Question 6

How can we kill a process that’s currently running in the foreground?

Answer 6

CTRL+c

Question 7

How can we suspend a process that’s currently running in the foreground?

Answer 7

CTRL+z

Question 8

What command should we use to activate a suspended process in the background?

Answer 8

bg

Question 9

What command should we use to bring a process from the background to the foreground?

Answer 9

fg

Question 10

What command should we use to kill a process?

Answer 10

kill

Question 11

What command should we use to list all the current jobs?

Answer 11

jobs

Question 12

What is the kill signal number?

Answer 12

-15 is the kill signal, -9 is a force kill signal.

root@CentOS # top &
[1] 3838
root@CentOS # kill -15 3838
[1]+  Stopped                 top