Essential for Linux Beginners! The pstree Command: A Visual Representation of Process Trees

In Linux systems, process management is a very important function. The pstree command displays running processes in a tree diagram format, which is more intuitive than the ps command, making the output visually appealing. Today, we will learn about this super useful command—pstree.1. What is the pstree Command?The pstree command is used to display running processes in a tree diagram format. It intuitively shows the hierarchical relationships between processes, helping users understand which processes are derived from others. This way, users can more easily comprehend the hierarchy of processes in the system and quickly locate all child processes of a specific service or application.Before diving deeper into the pstree command, it is recommended to check its official documentation to understand all available options and usage. Enter the following command in the terminal:

man pstree

2. Usage of the pstree CommandBasic command format:

pstree [options] [PID/username]

Common options: -a Show command line arguments -p Show each process’s PID -c Force expand identical subtrees -n Sort processes with the same ancestor by PID instead of by name -u Show the owner of the process -h Highlight the specified process (by name/PID) -g Show process group ID in the output -l View an untruncated process tree3. Example OperationsExample 1: Display all process trees

pstree # This command will display a tree diagram of all running processes, # with the root node usually being init (or systemd in modern Linux systems), # which is the ancestor of all user space processes.

Example 2: Display processes of a specified user

pstree shishun # This command will display all processes owned by the specified user shishun.

Example 3: Display the tree structure of a specified process ID

pstree 123 # This command will display the tree structure of the process with ID 123.

Example 4: Display process IDs

pstree -p # This command will display the name and PID of each process.

Example 5: Display the owner of processes

pstree -u # This command will display the owner of each process.

Example 6: Highlight specified processes

pstree -h # or pstree -H 1234 # The first command will highlight the process tree of the current shell, # the second command will highlight the process with PID 1234.

Example 7: Display process group IDs

pstree -g # This command will display the process group ID in the output.

Example 8: Force expand identical subtrees

pstree -c # This command will force expand identical subtrees instead of merging them with brackets.

Example 9: View an untruncated process tree

pstree -l # This command will view an untruncated process tree, with output expanded into multiple lines for better readability.

4. Output ExplanationThe output of the pstree command is a tree diagram that shows the parent-child relationships between processes. Here are some key points:

Root node: Usually init or systemd, which is the ancestor of all user space processes. Parent and child processes: Each node in the tree represents a process, with branches indicating parent-child relationships. Parent processes are on the upper level, and child processes are on the lower level. Threads: Threads are displayed in curly braces after the process name, e.g., process_name{thread_name}. Duplicate processes: Identical process branches are merged with brackets and prefixed with a count of duplicates, e.g., 4*[getty].

5. Practical TipsScenario 1: Diagnosing system issuesWhen the system experiences performance issues or anomalies, you can use pstree to view the hierarchy of processes, helping to identify which processes are the root of the problem:

pstree -p # This command will display the PID of all processes, helping to quickly locate the issue.

Scenario 2: Monitoring processes of a specific userYou can use the following command to monitor processes of a specific user:

pstree shishun # This command will display all processes of the specified user.

Scenario 3: Highlighting key processesYou can use the following command to highlight key processes:

pstree -H1234 # This command will highlight the process with PID 1234.

6. NotesPermission requirements: The pstree command usually does not require administrative privileges to execute, but if you want to view processes of other users, you may need administrative privileges.Output format: The output format of the pstree command may vary depending on the options used. It is recommended to check the man page for detailed information.7. Interactive SectionQuestion 1: How to use the pstree command to display a tree diagram of all running processes?Question 2: How to highlight a specified process when using the pstree command?If you already know the answers, or if you have other questions while using the pstree command, feel free to leave a comment for discussion! Let’s communicate and progress together.

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