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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:[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:
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#
PID TTY STAT TIME COMMAND
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:
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#
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
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:
For a complete list of available command line options, refer to the *ps*(1) manual page.
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:
For each listed process, the [command]#top# command displays the process ID (`PID`), the effective username of the process owner (`USER`), the priority (`PR`), the nice value (`NI`), the amount of virtual memory the process uses (`VIRT`), the amount of non-swapped physical memory the process uses (`RES`), the amount of shared memory the process uses (`SHR`), the percentage of the CPU (`%CPU`) and memory (`%MEM`) usage, the cumulated CPU time (`TIME+`), and the name of the executable file (`COMMAND`). For example:
~]$ top
top - 19:22:08 up 5:53, 3 users, load average: 1.08, 1.03, 0.82
Tasks: 117 total, 2 running, 115 sleeping, 0 stopped, 0 zombie
Cpu(s): 9.3%us, 1.3%sy, 0.0%ni, 85.1%id, 0.0%wa, 1.7%hi, 0.0%si, 2.6%st
Mem: 761956k total, 617256k used, 144700k free, 24356k buffers
Swap: 1540092k total, 55780k used, 1484312k free, 256408k cached
xref:System_Monitoring_Tools.adoc#interactive-top-command[Interactive top commands] contains useful interactive commands that you can use with [command]#top#. For more information, refer to the *top*(1) manual page.
Interactive top commands
indexterm:[gnome-system-monitor]indexterm:[System Monitor] The `Processes` tab of the [application]*System Monitor* tool allows you to view, search for, change the priority of, and kill processes from the graphical user interface.
To start the [application]*System Monitor* tool, either select menu:Applications[System Tools > `System Monitor`pass:attributes[{blank}]] from the Activities menu, or type [command]#gnome-system-monitor# at a shell prompt. Then click the `Processes` tab to view the list of running processes.
For each listed process, the [application]*System Monitor* tool displays its name (`Process Name`), user (`User`), percentage of the CPU usage (`% CPU`), process ID (`ID`), memory usage (`Memory`), total disk read and write (`Disk read total` and `Disk write total`), current disk read and write (`Disk read` and `Disk write`), and prioritiy (`Priority`). To sort the information by a specific column in ascending order, click the name of that column. Click the name of the column again to toggle the sort between ascending and descending order.