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System Monitoring Tools
indexterm:[system information,gathering]indexterm:[information,about your system] In order to configure the system, system administrators often need to determine the amount of free memory, how much free disk space is available, how the hard drive is partitioned, or what processes are running.
Viewing System Processes
indexterm:[system information,processes]indexterm:[processes]
Using the ps Command
indexterm:[ps] The [command]#ps# command allows you to display information about running processes. It produces a static list, that is, a snapshot of what is running when you execute the command. If you want a constantly updated list of running processes, use the [command]#top# command or the [application]*System Monitor* application instead.
To list all processes that are currently running on the system including processes owned by other users, type the following at a shell prompt:
[command]#ps# [option]`ax`
For each listed process, the [command]#ps ax# command displays the process ID (`PID`), the terminal that is associated with it (`TTY`), the current status (`STAT`), the cumulated CPU time (`TIME`), and the name of the executable file (`COMMAND`). For example:
~]$ [command]#ps ax#
1 ? Ss 0:02 /usr/lib/systemd/systemd --system --deserialize 20
2 ? S 0:00 [kthreadd]
3 ? S 0:00 [ksoftirqd/0]
5 ? S 0:00 [kworker/u:0]
6 ? S 0:00 [migration/0]
_[output truncated]_
To display the owner alongside each process, use the following command:
[command]#ps# [option]`aux`
Apart from the information provided by the [command]#ps ax# command, [command]#ps aux# displays the effective username of the process owner (`USER`), the percentage of the CPU (`%CPU`) and memory (`%MEM`) usage, the virtual memory size in kilobytes (`VSZ`), the non-swapped physical memory size in kilobytes (`RSS`), and the time or date the process was started. For instance:
~]$ [command]#ps aux#
root 1 0.0 0.3 53128 2988 ? Ss 13:28 0:02 /usr/lib/systemd/systemd --system --deserialize 20
root 2 0.0 0.0 0 0 ? S 13:28 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? S 13:28 0:00 [ksoftirqd/0]
root 5 0.0 0.0 0 0 ? S 13:28 0:00 [kworker/u:0]
root 6 0.0 0.0 0 0 ? S 13:28 0:00 [migration/0]
_[output truncated]_
You can also use the [command]#ps# command in a combination with [command]#grep# to see if a particular process is running. For example, to determine if [application]*Emacs* is running, type:
~]$ [command]#ps ax | grep emacs#
2625 ? Sl 0:00 emacs
For a complete list of available command line options, refer to the *ps*(1) manual page.
Using the top Command
indexterm:[system information,processes,currently running]indexterm:[top] The [command]#top# command displays a real-time list of processes that are running on the system. It also displays additional information about the system uptime, current CPU and memory usage, or total number of running processes, and allows you to perform actions such as sorting the list or killing a process.
To run the [command]#top# command, type the following at a shell prompt: