How to Use the Command 'pgrep' (with examples)

The pgrep command is a powerful tool in Unix-like operating systems that allows users to search for processes currently running on the system. This command is beneficial for system administrators and developers who often need to locate or interact with specific processes based on their attributes, such as process name, user, or command-line parameters. By using pgrep, you can avoid manually sifting through the process list, streamlining the process of finding relevant information quickly and efficiently.

Use case 1: Return PIDs of any running processes with a matching command string

Code:

pgrep process_name

Motivation:

Imagine a scenario where you are managing a server, and you wish to find all processes that are currently running a particular application, for example, “apache2”. Manually scrolling through the process list using tools like ps might be time-consuming and error-prone. Instead, using pgrep, you can quickly retrieve a list of process IDs (PIDs) associated with processes whose names match the specified string, allowing for faster systems diagnostics and management.

Explanation:

• pgrep: The command used to search for processes currently running.
• process_name: This is the argument where you specify the name of the process you are interested in. The command will return the PIDs of all processes whose names contain this string.

Example Output:

1234
2345
3456

The numbers shown are example PIDs of processes whose names contain “process_name”.

Use case 2: Search for processes including their command-line options

Code:

pgrep --full "process_name parameter"

Motivation:

Consider you have a script or application that can be invoked with several command-line options, and you need to find instances of this script running with specific options. Using pgrep --full, you can match the entire command line, including the options, making it straightforward to find exactly the right process for further inspection or interaction.

Explanation:

• pgrep: The command for finding processes.
• --full: This option tells pgrep to match against the complete command line rather than just the process name. It’s helpful for cases where different instances of the same process might have different command-line arguments.
• "process_name parameter": This string encompasses both the process name and any command-line parameters or options you want to match exactly.

Example Output:

4567
5678

These numbers represent the PIDs of processes running with “process_name parameter” in their command line.

Use case 3: Search for processes run by a specific user

Code:

pgrep --euid root process_name

Motivation:

In managing multi-user systems, it is often necessary to find processes executed by a specific user, especially by the superuser, ‘root’. This might be necessary for troubleshooting, monitoring, or auditing purposes. By using pgrep --euid, you can filter out processes not only by their name but also by the user ID of the owner of these processes.

Explanation:

• pgrep: Initiates the search for processes.
• --euid: A flag indicating that the search should be filtered by the effective user ID. This option is useful when you are interested in processes initiated by a particular user, enhancing audit and monitoring tasks.
• root: The specific user (by name or user ID) whose processes you want to locate.
• process_name: The target process name you want to find; in combination with --euid, this targets processes named “process_name” owned by the user ‘root’.

Example Output:

7890
8901

These are the PIDs of “process_name” processes that are run by the root user.

Conclusion:

The pgrep command is a versatile tool that simplifies the process of locating and managing processes on a Unix-like system. Whether you are trying to find processes by name, command-line parameters, or by the user who initiated them, pgrep offers a straightforward solution. By utilizing its options, such as --full and --euid, users can conduct complex and specific process searches with ease. This tool is invaluable for system administration tasks, aiding in efficient system management and monitoring activities.