Practice Exercise: Listing Processes with ps and top
Objectives
- Learn how to list and monitor running processes using
psandtopcommands. - Gain practical experience in process management on a Linux system.
Scenario
Understanding how to list and monitor processes is crucial for Linux system administrators. In this practice exercise, you will explore the ps and top commands, which provide insights into the processes running on a Linux system.
Before you begin...
Make sure that you have read the Lab Environment before starting the exercise.
Tasks
Task 1: Using ps to List Processes
- Open a terminal on your Linux system.
- Execute the
pscommand to list the running processes. - Observe the default output format, which includes process IDs (PIDs), terminal IDs (TIDs), and process names.
- Explore various options and arguments of the
pscommand to customize the process listing (e.g.,ps auxorps -effor a more detailed list). - What are the three options that ps accepts?
[intern@intern-a1t-inf-lnx1 ~]$ ps
PID TTY TIME CMD
PID TTY TIME CMD
22462 pts/1 00:00:00 bash
22503 pts/1 00:00:00 ps
[intern@intern-a1t-inf-lnx1 ~]$ ps aux
[intern@intern-a1t-inf-lnx1 ~]$ ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 1.2 172588 12392 ? Ss Oct11 0:05 /sbin/init
root 2 0.0 0.0 0 0 ? S Oct11 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? I< Oct11 0:00 [rcu_gp]
root 4 0.0 0.0 0 0 ? I< Oct11 0:00 [rcu_par_gp]
root 5 0.0 0.0 0 0 ? I< Oct11 0:00 [slub_flushwq]
root 6 0.0 0.0 0 0 ? I< Oct11 0:00 [netns]
root 8 0.0 0.0 0 0 ? I< Oct11 0:00 [kworker/0:0H-events_highpri]
root 10 0.0 0.0 0 0 ? I< Oct11 0:00 [mm_percpu_wq]
root 12 0.0 0.0 0 0 ? I Oct11 0:00 [rcu_tasks_kthread]
...
...
...
intern 22462 0.0 0.3 224920 3840 pts/1 Ss 06:30 0:00 -bash
root 22496 0.0 0.0 0 0 ? R 06:30 0:00 [kworker/u2:0-events_unbound]
root 22501 0.0 0.0 0 0 ? I 06:40 0:00 [kworker/0:2-cgroup_pidlist_destroy]
root 22502 0.0 0.0 0 0 ? I 06:40 0:00 [kworker/0:3-events]
intern 22506 0.0 0.3 257436 3840 pts/1 R+ 06:45 0:00 ps aux
[intern@intern-a1t-inf-lnx1 ~]$ ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 Oct11 ? 00:00:05 /sbin/init
root 2 0 0 Oct11 ? 00:00:00 [kthreadd]
root 3 2 0 Oct11 ? 00:00:00 [rcu_gp]
root 4 2 0 Oct11 ? 00:00:00 [rcu_par_gp]
root 5 2 0 Oct11 ? 00:00:00 [slub_flushwq]
root 6 2 0 Oct11 ? 00:00:00 [netns]
root 8 2 0 Oct11 ? 00:00:00 [kworker/0:0H-events_highpri]
root 10 2 0 Oct11 ? 00:00:00 [mm_percpu_wq]
...
...
intern 22455 22452 0 06:30 ? 00:00:00 (sd-pam)
intern 22461 22444 0 06:30 ? 00:00:00 sshd: intern@pts/1
intern 22462 22461 0 06:30 pts/1 00:00:00 -bash
root 22496 2 0 06:30 ? 00:00:00 [kworker/u2:0-events_unbound]
root 22502 2 0 06:40 ? 00:00:00 [kworker/0:3-mm_percpu_wq]
intern 22507 22462 0 06:46 pts/1 00:00:00 ps -ef
Task 2: Viewing Process Hierarchy
- Use the
pscommand to display processes in a hierarchical tree structure. - What is the parameter needed to achieve this?
- Identify the parent-child relationships between processes.
- Note the PPID (Parent Process ID) column to understand which process spawned other processes.
[intern@intern-a1t-inf-lnx1 ~]$ pstree
systemd─┬─NetworkManager───2*[{NetworkManager}]
├─2*[agetty]
├─atd
├─auditd───{auditd}
├─crond
├─dbus-daemon
├─node_exporter───3*[{node_exporter}]
├─polkitd───5*[{polkitd}]
├─rsyslogd───2*[{rsyslogd}]
├─sleep
├─splunkd─┬─splunkd
│ └─43*[{splunkd}]
├─sshd───sshd───sshd───bash───pstree
├─2*[systemd───(sd-pam)]
├─systemd-journal
├─systemd-logind
├─systemd-udevd
└─tuned───5*[{tuned}]
[intern@intern-a1t-inf-lnx1 ~]$ ps aux --forest
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 2 0.0 0.0 0 0 ? S Oct11 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? I< Oct11 0:00 \_ [rcu_gp]
root 4 0.0 0.0 0 0 ? I< Oct11 0:00 \_ [rcu_par_gp]
root 5 0.0 0.0 0 0 ? I< Oct11 0:00 \_ [slub_flushwq]
root 6 0.0 0.0 0 0 ? I< Oct11 0:00 \_ [netns]
root 8 0.0 0.0 0 0 ? I< Oct11 0:00 \_ [kworker/0:0H-events_highpri]
root 10 0.0 0.0 0 0 ? I< Oct11 0:00 \_ [mm_percpu_wq]
root 12 0.0 0.0 0 0 ? I Oct11 0:00 \_ [rcu_tasks_kthread]
root 13 0.0 0.0 0 0 ? I Oct11 0:00 \_ [rcu_tasks_rude_kthread]
root 14 0.0 0.0 0 0 ? I Oct11 0:00 \_ [rcu_tasks_trace_kthread]
root 15 0.0 0.0 0 0 ? S Oct11 0:00 \_ [ksoftirqd/0]
root 16 0.0 0.0 0 0 ? I Oct11 0:01 \_ [rcu_preempt]
...
...
...
root 20370 0.0 13.9 311256 135576 ? Ssl Oct12 1:11 splunkd --under-systemd --systemd-delegate=yes -p 8089 _internal_launch_und
root 20404 0.0 2.1 133352 21272 ? Ss Oct12 0:00 \_ [splunkd pid=20370] splunkd --under-systemd --systemd-delegate=yes -p 8
intern 22452 0.0 1.1 89464 11116 ? Ss 06:30 0:00 /usr/lib/systemd/systemd --user
intern 22455 0.0 0.8 232196 8124 ? S 06:30 0:00 \_ (sd-pam)
Task 3: Monitoring Processes with top
- Launch the
topcommand in your terminal. - Observe the dynamic real-time display of system statistics and process information.
- Pay attention to CPU usage, memory usage, load averages, and the list of running processes.
- Use the
qkey to exittopwhen you're done.
[intern@intern-a1t-inf-lnx1 ~]$ top
top - 03:19:22 up 5 days, 1:45, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 160 total, 1 running, 159 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.3 us, 0.3 sy, 0.0 ni, 99.0 id, 0.0 wa, 0.0 hi, 0.3 si, 0.0 st
MiB Mem : 946.4 total, 166.9 free, 279.4 used, 500.0 buff/cache
MiB Swap: 0.0 total, 0.0 free, 0.0 used. 472.1 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 172588 10416 7768 S 0.0 1.1 0:06.98 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.04 kthreadd
3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp
4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par_gp
5 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 slub_flushwq
6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 netns
8 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/0:0H-events_highpri
Task 4: Sorting and Filtering Processes in top
- Start
topagain. - Experiment with sorting options by pressing keys like
P,M, andT. - Use the
okey to apply filters. For example, pressoand enter a filter likeUSER eq <username>to display processes for a specific user. - Explore other sorting and filtering options available in
top.
[intern@intern-a1t-inf-lnx1 ~]$ top
Task 5: Sending Signals to Processes
- Identify a process from the
psortoplist that you want to interact with. - Note its PID (Process ID).
- Use the
killcommand to send a signal to the selected process (e.g.,kill <PID>to gracefully terminate it). - Observe how the process responds to different signals.
# Run sleep in the background
[intern@intern-a1t-inf-lnx1 ~]$ sleep 1000000 &
[intern@intern-a1t-inf-lnx1 ~]$ ps aux | grep sleep
intern 22512 0.0 0.1 217088 1792 pts/1 S 06:49 0:00 sleep 1000000
intern 22513 0.0 0.2 221944 2304 pts/1 R+ 06:48 0:00 grep --color=auto sleep
# Kill the sleep process forcefully using the SIGKILL (-9) signal
[intern@intern-a1t-inf-lnx1 ~]$ kill -9 22512
[intern@intern-a1t-inf-lnx1 ~]$
[1]+ Killed sleep 1000000
# Run sleep in the background
[intern@intern-a1t-inf-lnx1 ~]$ sleep 1000000 &
[intern@intern-a1t-inf-lnx1 ~]$ ps aux | grep sleep
intern 22512 0.0 0.1 217088 1792 pts/1 S 06:49 0:00 sleep 1000000
intern 22513 0.0 0.2 221944 2304 pts/1 R+ 06:48 0:00 grep --color=auto sleep
# Kill the sleep process forcefully using the SIGKILL (-9) signal
[intern@intern-a1t-inf-lnx1 ~]$ kill -9 22512
[intern@intern-a1t-inf-lnx1 ~]$
[1]+ Killed sleep 1000000
Conclusion
This practice exercise has provided you with practical experience in listing and monitoring processes using the ps and top commands on a Linux system. You've learned how to customize process listings, view process hierarchies, monitor system statistics, sort and filter processes, and send signals to control processes. These skills are essential for system administrators to efficiently manage processes and troubleshoot system performance.