Home > Articles > Certification > Other IT

  • Print
  • + Share This
This chapter is from the book

Monitoring System Performance

Every time a program or command is run, a process is created for it. These processes are all unique and identified by the process identification (PID) that becomes allocated to it. System processes are critical to keeping the system up and running or providing services to clients. Management of processes can help keep the system stable or help when the system becomes unstable. Here are some of the process management commands you can use:


Displays information about running processes


Terminates a process


Finds a process based on its PID


Displays all processes related to a service or command


Monitors system resources (similar to Task Manager in Windows)


Adjusts the priority of a particular process

First, let's look at the processes the root user currently owns by using the ps command:

# ps
  PID TTY           TIME CMD
 4474 pts/3    00:00:00 bash
 4506 pts/3    00:00:00 ps

The ps command includes a number of options for producing different types of output, including viewing all processes currently running on the system.

To view processes with more detailed information, you can use the following command:

# ps u
root   2387  0.0  0.1   1660   424 tty1  Ss+  07:30   0:00 /sbin/mingetty tty1
root   2388  0.0  0.1   1660   420 tty2  Ss+  07:30   0:00 /sbin/mingetty tty2
root   2389  0.0  0.1   1660   420 tty3  Ss+  07:30   0:00 /sbin/mingetty tty3
root   2390  0.0  0.1   1660   420 tty4  Ss+  07:30   0:00 /sbin/mingetty tty4
root   2391  0.0  0.1   1660   448 tty5  Ss+  07:30   0:00 /sbin/mingetty tty5
root   2392  0.0  0.1   1660   420 tty6  Ss+  07:30   0:00 /sbin/mingetty tty6

Here, you see not only the PID, but also the CPU and memory utilization. A common set of options that I use when working with the ps command is aux combined with the grep command to weed out anything I'm not interested in. This way, I can get detailed information about a particular process. Say you'd like to see what information is available about any process pertaining to the SSH service:

# ps aux | grep ssh
root      4286  0.0  0.1  62616  1216 ?   Ss  Sep23  0:00 /usr/sbin/sshd
root     15872  0.0  0.3  90116  3248 ?   Ss  10:06  0:00 sshd: user01 [priv]
user01   15874  0.0  0.1  90116  1740 ?   S   10:06  0:00 sshd: user01@pts/0
user01   15921  0.0  0.0  61176   728 pts/0  R+  10:14  0:00 grep ssh

You also could use

# ps aux

With this command, however, you would receive 59 lines of output that you would have had to go through to view those 4 lines that you actually need. You can see how narrowing down your output can be really helpful.

Let's also look at some of the other options the ps command offers:

$ ps—help
********* simple selection *********  ********* selection by list *********
-A all processes                        -C by command name
-N negate selection                   -G by real group ID (supports names)
-a all w/ tty except session leaders  -U by real user ID (supports names)
-d all except session leaders         -g by session OR by effective group name
-e all processes                      -p by process ID
T  all processes on this terminal     -s processes in the sessions given
a  all w/ tty, including other users  -t by tty
g  OBSOLETE—DO NOT USE              -u by effective user ID (supports names)
r  only running processes             U  processes for specified users
x  processes w/o controlling ttys     t  by tty
*********** output format **********  *********** long options ***********
-o,o user-defined  -f full            --Group --User --pid --cols --ppid
-j,j job control   s  signal          --group --user --sid --rows --info
-O,O preloaded -o  v  virtual memory  --cumulative --format --deselect
-l,l long          u  user-oriented   --sort --tty --forest --version
-F   extra full    X  registers       --heading --no-heading --context
                     ********* misc options *********
-V,V  show version      L  list format codes  f  ASCII art forest
-m,m,-L,-T,H  threads   S  children in sum    -y change -l format
-M,Z  security data     c  true command name  -c scheduling class
-w,w  wide output       n  numeric WCHAN,UID  -H process hierarchy

You can see here that there are numerous output formats and sort features. Knowing how to manipulate the output of the ps command and find what you're looking for really helps when troubleshooting on the exams, but it also plays a huge role in troubleshooting in the real world.

What happens if one of the processes running on your system becomes out of control? In that case, you can use the kill command to terminate the process, even if it isn't responding (also called a runaway process). To use the kill command, however, you need to know the PID of the process that you want to kill (are you starting to see why the ps command is so helpful?).

Syntax: kill PID

If you want to stop the SSH service because it isn't responding, you just have to look for the PID associated with the SSH daemon. If you look back at the output, you can see this is PID 4286. To kill the process forcefully and effectively stop the SSH service, you can do the following:

# kill 4286

Sometimes if the kill command doesn't work the way you intended it to, you can also call it with the -9 option to give it priority on the system:

# kill -9 4286

What happens if you don't know the PID of the process you want to terminate? How could you look that up if you weren't sure what to query from the output of the ps command? There are actually two other commands you can use to determine the PID(s) of a service or command: pidof and pgrep.

First, let's look at pidof, to which you can pass just the name of the service or daemon. To find the PID(s) belonging to the SSH service, use the following:

# pidof sshd
15874 15872 4286

To achieve the same information in an easier-to-read format, you can use the pgrep command:

# pgrep sshd

It's good to know that you can hunt down and kill processes or even just find out how many are running, but what if you need more information? Suppose you need to know how much of the CPU a particular process is taking up? Let's look at the final command: top. This command gives you an overview of processes on the system, including memory usage, CPU utilization, and more.

To check out the system overall, issue the following command and you get results similar to those shown in Figure 9-1:


Figure 9-1

Figure 9-1 Results of running .

The output in Figure 9-1 shows real-time information about the system resources. You can use the q to quit from the top command.

When you're comfortable working with processes, you can then make some more advanced adjustments, such as changing the priority of a particular process. Let's say that you have a custom application running on your system. You can use the renice command to give that particular process higher priority on the CPU.

Syntax: renice <priority> [options]


-p PID

Changes process priority for a particular PID

-u user

Changes process priority for a particular user(s)

The priority values range from –20 (first priority) to 20 (dead last priority). Only the root user may set processes to use a priority under 0. Going back to the example, you can give the application extra priority by using the following:

# renice -2 3874

This command changes the application process (3874) to have better priority than its default priority of 0. Knowing how to work with system processes and extract information from your system will help you become a better system administrator. It can also help you troubleshoot faster on the Red Hat exams.

In the next section, we look at job scheduling, which can be combined with some of the commands just covered to automate system monitoring.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020