ps (list processes) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the ps command do in Linux?

The ps command lists the currently running processes on your system. It shows details like process ID, terminal, CPU usage, and command name.

beginner

What does the option ps aux show?

ps aux shows all running processes for all users with detailed information including user, CPU and memory usage, start time, and command.

beginner

How can you use ps to find processes by a specific user?

Use ps -u username to list processes owned by that user only.

beginner

What does the ps -ef command do?

ps -ef lists all processes in full-format listing, showing detailed info like UID, PID, PPID, start time, and command.

beginner

How can you combine ps with grep to find a process?

You can run ps aux | grep process_name to filter and find processes matching the name you want.

Which ps option shows all processes with detailed info?

A ps -u

B ps -l

C ps aux

D ps -t

ps aux lists all processes for all users with detailed information.

What does ps -u username do?

A Shows processes for all users

B Shows processes by terminal

C Shows only running system services

D Shows processes for the specified user

The -u option filters processes by the specified username.

How do you find a process named 'firefox' using ps?

A ps -u firefox

B ps aux | grep firefox

C ps -ef firefox

D ps firefox

Using ps aux | grep firefox filters the process list to show only lines containing 'firefox'.

What information does ps -ef NOT show?

A User's home directory

B Parent Process ID (PPID)

C Process ID (PID)

D Start time of the process

ps -ef does not show the user's home directory.

Which command lists processes running on your current terminal?

A ps

B ps aux

C ps -ef

D ps -u

Running ps without options lists processes running in your current terminal session.

Explain how to list all running processes on a Linux system with detailed information.

Think about showing every process regardless of user.

Describe how to find a specific process by name using the command line.

Combine two commands with a pipe.

Practice

1. What does the ps command do in Linux?

easy

A. It shows the disk usage of files and folders.

B. It lists the currently running processes on the system.

C. It displays the network connections.

D. It updates the system software.

Solution

1. Step 1: Understand the purpose of ps

   The ps command is used to show processes running on the system.

2. Step 2: Compare with other options

   Disk usage is handled by du, network connections by netstat or ss, and software updates by apt or yum.

3. Final Answer:

   It lists the currently running processes on the system. -> Option B

4. Quick Check:

   ps shows running processes [OK]

Hint: Remember: ps = process status, shows running programs [OK]

Common Mistakes:

• Confusing ps with disk or network commands
• Thinking ps updates software
• Assuming ps shows file sizes

2. Which of the following is the correct syntax to list all processes with full details using ps?

easy

A. ps -l

B. ps -xv

C. ps auxf

D. ps -ef

Solution

1. Step 1: Identify the common option for full details

   The -ef option with ps lists all processes with full details.

2. Step 2: Check other options

   ps -xv is an invalid combination, ps auxf displays a tree view rather than a plain list, and ps -l shows limited info for current processes.

3. Final Answer:

   ps -ef -> Option D

4. Quick Check:

   ps -ef shows all processes fully [OK]

Hint: Use ps -ef for full process list [OK]

Common Mistakes:

• Using ps -xv which is invalid
• Confusing ps auxf as a single option
• Using ps -l which shows limited info

3. What will be the output of the command ps -e | grep sshd if the sshd process is running?

medium

A. It will show the sshd process details in the list.

B. It will show an error because grep cannot be used with ps.

C. It will show all processes except sshd.

D. It will show nothing because sshd is filtered out.

Solution

1. Step 1: Understand ps -e and pipe to grep

   ps -e lists all processes; piping to grep sshd filters lines containing 'sshd'.

2. Step 2: Interpret the output if sshd is running

   If sshd is running, its process line will appear in the output.

3. Final Answer:

   It will show the sshd process details in the list. -> Option A

4. Quick Check:

   ps -e | grep sshd shows sshd if running [OK]

Hint: Pipe ps output to grep to find specific processes [OK]

Common Mistakes:

• Thinking grep causes error with ps
• Assuming grep excludes matching lines
• Believing sshd won't appear if running

4. You run ps -ef | grep but get an error. What is the likely cause?

medium

A. You forgot to provide a search pattern after grep.

B. The ps command does not support pipes.

C. The -ef option is invalid for ps.

D. grep cannot be used with ps output.

Solution

1. Step 1: Analyze the command structure

   ps -ef outputs all processes; piping to grep requires a pattern to search.

2. Step 2: Identify the error cause

   Without a pattern, grep throws an error because it expects a search term.

3. Final Answer:

   You forgot to provide a search pattern after grep. -> Option A

4. Quick Check:

   grep needs a pattern after it [OK]

Hint: Always give grep a pattern to avoid errors [OK]

Common Mistakes:

• Thinking ps can't pipe output
• Believing -ef is invalid
• Assuming grep works without a pattern

5. You want to list all processes owned by user 'alice' with detailed info. Which command should you use?

hard

A. ps aux | grep alice

B. ps -ef | grep alice

C. ps -u alice -f

D. ps -U alice

Solution

1. Step 1: Understand options for user filtering

   ps -u alice lists processes for user alice; -f adds full details.

2. Step 2: Compare other options

   Using ps -ef | grep alice or ps aux | grep alice relies on grep which may match username in other fields, not just owner. ps -U alice lists processes by real user ID but lacks full details.

3. Final Answer:

   ps -u alice -f -> Option C

4. Quick Check:

   ps -u alice -f lists alice's processes fully [OK]

Hint: Use ps -u username -f for detailed user processes [OK]

Common Mistakes:

• Using grep which may show unrelated lines
• Using -U without details
• Confusing -u and -U options