Linux display currently running processes

How to List and Manage Running Processes in Linux

Learn essential commands to view, filter, and understand currently running processes on your Linux system, crucial for monitoring and troubleshooting.

Understanding what processes are running on your Linux system is fundamental for system administration, troubleshooting, and performance monitoring. Whether you're trying to identify resource hogs, debug a misbehaving application, or simply keep an eye on system health, knowing how to list and interpret process information is a vital skill. This article will guide you through the most common and powerful commands used to inspect running processes in Linux.

The ps Command: Process Status

The ps command (process status) is one of the oldest and most frequently used utilities for displaying information about currently running processes. By default, ps shows processes associated with your current terminal session. To get a more comprehensive view, you'll typically use it with various options.

ps aux
ps -ef

Common ps command variations for comprehensive process listings.

Let's break down the common options:

• a: Shows processes for all users.
• u: Displays user-oriented format, including CPU/memory usage, start time, and command.
• x: Includes processes not attached to a terminal.
• -e: Selects all processes.
• -f: Displays full-format listing, providing more details like parent process ID (PPID).

The output of ps aux typically includes columns like USER, PID, %CPU, %MEM, VSZ, RSS, TTY, STAT, START, TIME, and COMMAND. Understanding these columns is key to interpreting the output.

flowchart LR
    A[User Executes `ps aux`] --> B{Kernel Process Table}
    B --> C[Retrieve Process Data]
    C --> D[Format Output]
    D --> E[Display to User]
    E --"PID, %CPU, COMMAND, etc."--> F[User Interpretation]

Simplified flow of the ps command execution.

The top Command: Real-time Process Monitoring

While ps provides a snapshot of processes, top offers a dynamic, real-time view of your system's running processes. It displays a constantly updated list of processes, ordered by CPU usage by default, along with system summary information like CPU load, memory usage, and swap space. This makes top invaluable for identifying processes that are currently consuming the most resources.

top

Execute top for an interactive, real-time process view.

Inside top, you can use several interactive commands:

• k: Kill a process (you'll be prompted for the PID).
• r: Renice a process (change its priority).
• P: Sort by CPU usage (default).
• M: Sort by memory usage.
• q: Quit top.

Filtering and Searching Processes with grep

Often, you're not interested in all processes, but rather specific ones. Combining ps or top with grep allows you to filter the output and find exactly what you're looking for. This is particularly useful for finding processes by name or user.

ps aux | grep firefox
ps -ef | grep nginx
ps aux | grep [m]ysql

Filtering process lists using grep.

The [m]ysql trick in the last example is a common way to prevent grep from listing itself in the output when searching for a process name. By putting one character of the search term in square brackets, grep won't match its own command line.

Managing Processes: kill and killall

Once you've identified a problematic process, you might need to terminate it. The kill command sends signals to processes, with the default signal being SIGTERM (15), which requests a graceful shutdown. If a process doesn't respond, SIGKILL (9) can be used for an immediate, forceful termination.

# Gracefully terminate process with PID 12345
kill 12345

# Forcefully terminate process with PID 54321
kill -9 54321

# Terminate all processes named 'my_app'
killall my_app

Using kill and killall to manage processes.