02. Viewing Processes ps
We can easily view processes, using ps (process status). This only displays the processes that run from the current terminal, so are limited.
$ ps
PID TTY TIME CMD
2696 pts/0 0:00:00 bash
2745 pts/0 0:00:00 psAt the most basic level, there are only four columns.
- PID
- Process identifier. Necessary for sending signals.
- TTY
- Teletype. Refers to the terminal that is controlling the process. X programs and daemons don't have this, but text-mode programs do (eg. console, xterm or remote login session).
- TIME
- Amount of CPU time consumed by the process. The higher it is, the more resources it's taking from the computer.
- CMD
- The command that started the process.
Options with ps
As we'll see soon, the ps command comes with a variety of options. Depending on where these options originated, you may or may not need dashes preceding the option letter.
- BSD
- These come from an earlier Berkeley Software Distribution platform and require no dashes at all.
- Unix98
- These options are preceded by one dash, and are probably what you're most familiar with.
- GNU long
- As you're most likely familiar with, any GNU long options are preceded by two dashes (--).
More details with -ef
The -f option prints full format listing, meaning it includes additional parameters. The -e or -A options displays all processes (including daemon).
$ ps -efUID PID PPID C STIME TTY TIME CMD root 1 0 3 11:14 ? 00:00:00 /sbin/init root 2 0 0 11:14 ? 00:00:00 [kthreadd] root 3 2 0 11:14 ? 00:00:00 [ksoftirqd/0] root 4 2 0 11:14 ? 00:00:00 [kworker/0:0] root 5 2 0 11:14 ? 00:00:00 [kworker/0:0H] root 6 2 1 11:14 ? 00:00:00 [kworker/u2:0] root 7 2 0 11:14 ? 00:00:00 [rcu_sched] root 8 2 0 11:14 ? 00:00:00 [rcuos/0] root 9 2 0 11:14 ? 00:00:00 [rcu_bh]
You'll notice that some processes have a TTY of ?. This means that they have no controlling terminals. Many of these are daemon processes.
Here are some more parameters listed, adding onto the list above.
- UID
- User ID
- PPID
- Parent process identifier.
- C
- CPU utilization.
- STIME
- Time the process started.
Viewing user processes
To view all processes belonging to a user, use the -u option, followed by the username. If you want to view more than one username, separate the names with a comma.
$ ps -u JohnDoePC
# List all processes started by JohnDoePCMore details with aux
By attaching an aux option (no hyphen), we can see even more details. The a shows processes for all users, the u displays the process's owner, and the x shows processors not attached to a terminal.
Additionally, the w option shows the full command name, not just what fits on one line.
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.4 0.4 33772 2012 ? Ss 22:53 0:01 /sbin/init
root 2 0.0 0.0 0 0 ? S 22:53 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? S 22:53 0:00 [ksoftirqd/0]
root 4 0.0 0.0 0 0 ? S 22:53 0:00 [kworker/0:0]
root 5 0.0 0.0 0 0 ? S< 22:53 0:00 [kworker/0:0H]
root 6 0.0 0.0 0 0 ? S 22:53 0:00 [kworker/u2:0]
root 7 0.2 0.0 0 0 ? S 22:53 0:00 [rcu_sched]
root 8 0.0 0.0 0 0 ? S 22:53 0:00 [rcuos/0]
root 9 0.0 0.0 0 0 ? S 22:53 0:00 [rcu_bh]Here are some more variables that we see.
- USER
- User ID, or the owner of process.
- %CPU
- CPU usage as a percentage.
- %MEM
- Memory usage.
- VSZ
- Virtual memory size.
- RSS
- Resident set size - amount of physical memory (RAM) the process is using (kb).
- STAT
- Short for state. Reveals the current status of the process. See below for explanation.
- START
- Time when processor started.
- TIME
- Amount of CPU time process has acquired so far. Helpful for pinpointing runaway processes.
State Variables
Here are some variables that go along with the STAT column.
- D
- Uninterruptible sleep - waiting for I/O device, such as a drive.
- L
- Pages are locked into memory.
- R
- Running, or ready to run.
- S
- Sleeping, or waiting for user input.
- T
- Stopped
- Z
- Defunct, or a zombie process, aka a child process that stopped, but has not been cleaned up by parent process
- <
- High priority. Low niceness, meaning it takes up more resources.
- +
- In the foreground process group.
- N
- Low priority process. A nice process
- l
- Multi-threaded.
- s
- A session leader.
Inspecting current shell processes
To access the current shell's PID, use the shortcut $$. This evaluates to the current shell's PID.
$ ps u $$
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
JohnDoe 13030 0.0 0.0 27112 4092 pts/8 Ss 00:39 0:00 bashDisplaying process hierarchy
If you want to see where each process spawned from, we can use the -H, -f or --forest option. You'll see that each child process branches out with tabs, signifying its origin
$ ps -AH
...
1 ? 00:00:01 init
299 ? 00:00:00 upstart-udev-br
304 ? 00:00:00 systemd-udevd
517 ? 00:00:00 upstart-socket-
774 ? 00:00:00 upstart-file-br
783 ? 00:00:00 rsyslogd
792 ? 00:00:03 dbus-daemon
805 ? 00:00:00 ModemManager
816 ? 00:00:00 systemd-logind
818 ? 00:00:00 bluetoothd
850 ? 00:00:01 avahi-daemon
852 ? 00:00:00 avahi-daemon
...One drawback with using ps is that it's static - we cannot see the changes while they occur. For a more dynamic view of currently running processes, we can use the top command.
Take your Linux skills to the next level!
Command Line Kung Fu
Command Line Kung Fu is packed with dozens of tips and practical real-world examples. You won't find theoretical examples in this book. The examples demonstrate how to solve actual problems. The tactics are easy to find, too. Each chapter covers a specific topic and groups related tips and examples together.
$ Check price
(27+ reviews) Aching back from coding all day?
Inversion Therapy Table
Stretch out your back and relieve your back muscles with inversion therapy. This device counteracts the forces of gravity on the body by decompressing and elongating the spine. By using this product just ten minutes a day, you can be well on your way to improved circulation and posture while relieving muscle aches, back pain and stress.
$$ Check price(1,700+ reviews) Ad