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

The ps command in Unix-like operating systems is a potent tool for monitoring and managing system processes. It provides a snapshot of the current processes, showing details about each one, such as the process ID (PID), the parent process ID (PPID), CPU and memory usage, and much more. This command is essential for system administrators and users who need to understand what processes are running on their system or troubleshoot issues by examining process states.

Use case 1: List all running processes

Code:

ps aux

Motivation: By listing all running processes, users gain insight into what tasks their operating system is executing at any given moment. This information can be crucial for diagnosing high system load or identifying unauthorized applications running on the machine.

Explanation:

• aux: This option provides a comprehensive list of all processes. The a option tells ps to list processes of all users, including those without a terminal. The u option presents the output in a user-oriented format. The x option includes processes that are not associated with a terminal.

Example Output:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.1  22536  2672 ?        Ss   08:34   0:01 /usr/lib/systemd/systemd --system --deserialize 29
daemon    1020  0.0  0.5  94568 11672 ?        Ssl  08:34   0:10 /usr/bin/docker-containerd

Use case 2: List all running processes including the full command string

Code:

ps auxww

Motivation: The full command string helps in situations where the start of the command doesn’t provide sufficient context. This is especially useful for long commands where the critical details appear towards the completion of the command string.

Explanation:

• auxww: Besides what aux does, the ww in auxww forces ps to not truncate command lines in the display, making it possible to see long command lines in their entirety.

Example Output:

root         1  0.0  0.1  22536  2672 ?        Ss   08:34   0:01 /usr/lib/systemd/systemd --system --deserialize 29
daemon    1020  0.0  0.5  94568 11672 ?        Ssl  08:34   0:10 /usr/bin/docker-containerd --config /etc/docker/daemon.json

Use case 3: Search for a process that matches a string

Code:

ps aux | grep string

Motivation: Sometimes systems are running a multitude of processes, making it cumbersome to locate a specific one. This command simplifies this task by allowing users to filter processes containing a specific string, which could be part of the command or any attribute shown in the process list.

Explanation:

• ps aux: Generates a comprehensive list of all processes.
• | grep string: Pipes the list into grep, which searches for the specified ‘string’. This is particularly useful for isolating processes by name or attribute.

Example Output:

user1    21137  0.0  0.2 436656  9288 ?        Sl   09:00   0:00 some-process-name --option

Use case 4: Get the parent PID of a process

Code:

ps -o ppid= -p pid

Motivation: Each process has a parent process that initiated it, which can be critical when tracking process hierarchies or diagnosing process spawning issues, particularly in troubleshooting scenarios where understanding which process spawned another is required.

Explanation:

• -o ppid=: Customizes the output to show only the parent PID (PPID) by itself for clarity.
• -p pid: Specifies the process ID (PID) of the process for which you want to find the parent PID. This PID needs to be replaced with the actual PID of interest.

Example Output:

2345

Use case 5: Sort processes by memory usage

Code:

ps -m

Motivation: Sorting processes by memory usage helps quickly identify memory hogs on the system that can degrade performance. This is vital for optimization and ensuring smoother functioning of applications by mitigating excessive memory consumption.

Explanation:

• -m: Directs ps to sort the running processes by memory usage, placing those utilizing the most memory at the top.

Example Output:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND      
1835 user1     20   0 12.732g 1.625g  27468 S   1.0 10.5   1:12.53 application-x  
 2905 user1     20   0  457564 146344  11248 S   0.3  0.9   0:10.25 process-y

Use case 6: Sort processes by CPU usage

Code:

ps -r

Motivation: When a system experiences high load, sorting processes by CPU usage readily identifies which processes are taxing the CPU. This can be indispensable for maintaining optimal system performance and making informed decisions, such as which processes to terminate or allocate more resources to.

Explanation:

• -r: Arranges the processes list by CPU usage, which allows users to see which processes are consuming the most CPU time at the top of the list.

Example Output:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND      
 2905 user1     20   0  457564 146344  11248 S   5.5  0.9   0:10.25 cpu-intensive-process   
 1835 user1     20   0 12.732g 1.625g  27468 S   1.0 10.5   1:12.53 less-active-process

Conclusion:

The ps command provides a powerful and versatile set of functionalities for monitoring, analyzing, and managing system processes. Whether you’re a system administrator troubleshooting system issues or an enthusiast exploring how Unix-like systems manage processes, these use cases illustrate how ps can give you the necessary insight into process management.