Understand the pstree Command
In this step, we will learn about the pstree command, which is a useful tool for visualizing the process hierarchy on a Linux system.
The pstree command displays a tree-like representation of the running processes, showing the parent-child relationships between them. This can be helpful for understanding the structure and dependencies of your system's processes.
To start, let's run the pstree command in the terminal:
$ pstree
systemd─┬─ModemManager─┬─dhclient
│ └─2*[{ModemManager}]
├─NetworkManager─┬─dhclient
│ └─2*[{NetworkManager}]
├─accounts-daemon───2*[{accounts-daemon}]
├─apache2─┬─apache2
│ └─2*[apache2]
├─atd
├─cron
├─dbus-daemon
├─dockerd─┬─containerd─┬─containerd-shim─┬─bash
│ │ │ └─3*[{containerd-shim}]
│ │ └─6*[{containerd}]
│ └─7*[{dockerd}]
├─gdm3─┬─Xorg
│ └─gnome-session-b─┬─gnome-shell
│ ├─ibus-daemon─┬─ibus-engine-sim
│ │ └─2*[{ibus-daemon}]
│ └─2*[{gnome-session-b}]
├─irqbalance
├─kerneloops
├─kube-proxy
├─kubelet
├─lightdm─┬─Xorg
│ └─lightdm───sh───fluxbox
├─lxcfs
├─lxd─┬─lxd
│ └─2*[{lxd}]
├─polkitd───2*[{polkitd}]
├─rsyslogd
├─snapd───10*[{snapd}]
├─ssh-agent
├─systemd-journal
├─systemd-logind
├─systemd-networkd
├─systemd-resolve
├─systemd-timesyn
├─systemd-udevd
├─udisksd───3*[{udisksd}]
├─unattended-upgr───2*[{unattended-upgr}]
├─upowerd───2*[{upowerd}]
├─user-manager───3*[{user-manager}]
└─whoopsie───2*[{whoopsie}]
The output shows a hierarchical view of the running processes, with the systemd process at the top as the parent of many other processes.
You can customize the output of pstree using various options. For example, to show only the process IDs (PIDs) instead of the process names, you can use the -p option:
$ pstree -p
systemd(1)─┬─ModemManager(577)─┬─dhclient(593)
│ └─2*[{ModemManager}(580,581)]
├─NetworkManager(572)─┬─dhclient(590)
│ └─2*[{NetworkManager}(573,574)]
├─accounts-daemon(531)───2*[{accounts-daemon}(532,533)]
├─apache2(688)─┬─apache2(689)
│ └─2*[apache2(690,691)]
├─atd(544)
├─cron(545)
├─dbus-daemon(530)
├─dockerd(688)─┬─containerd(701)─┬─containerd-shim(702)─┬─bash(703)
│ │ │ └─3*[{containerd-shim}(704,705,706)]
│ │ └─6*[{containerd}(707,708,709,710,711,712)]
│ └─7*[{dockerd}(689,690,691,692,693,694,695)]
├─gdm3(575)─┬─Xorg(586)
│ └─gnome-session-b(587)─┬─gnome-shell(588)
│ ├─ibus-daemon(589)─┬─ibus-engine-sim(592)
│ │ └─2*[{ibus-daemon}(590,591)]
│ └─2*[{gnome-session-b}(595,596)]
├─irqbalance(543)
├─kerneloops(546)
├─kube-proxy(697)
├─kubelet(696)
├─lightdm(576)─┬─Xorg(585)
│ └─lightdm(577)───sh(578)───fluxbox(579)
├─lxcfs(542)
├─lxd(698)─┬─lxd(699)
│ └─2*[{lxd}(700,701)]
├─polkitd(534)───2*[{polkitd}(535,536)]
├─rsyslogd(541)
├─snapd(694)───10*[{snapd}(695,696,697,698,699,700,701,702,703,704)]
├─ssh-agent(587)
├─systemd-journal(526)
├─systemd-logind(529)
├─systemd-networkd(527)
├─systemd-resolve(528)
├─systemd-timesyn(540)
├─systemd-udevd(525)
├─udisksd(537)───3*[{udisksd}(538,539,540)]
├─unattended-upgr(547)───2*[{unattended-upgr}(548,549)]
├─upowerd(535)───2*[{upowerd}(536,537)]
├─user-manager(586)───3*[{user-manager}(587,588,589)]
└─whoopsie(550)───2*[{whoopsie}(551,552)]
This shows the process IDs instead of the process names.
You can also use the -u option to display the user running each process:
$ pstree -u
systemd─┬─ModemManager─┬─dhclient
│ └─2*[{ModemManager}]
├─NetworkManager─┬─dhclient
│ └─2*[{NetworkManager}]
├─accounts-daemon───2*[{accounts-daemon}]
├─apache2─┬─apache2
│ └─2*[apache2]
├─atd
├─cron
├─dbus-daemon
├─dockerd─┬─containerd─┬─containerd-shim─┬─bash
│ │ │ └─3*[{containerd-shim}]
│ │ └─6*[{containerd}]
│ └─7*[{dockerd}]
├─gdm3─┬─Xorg
│ └─gnome-session-b─┬─gnome-shell
│ ├─ibus-daemon─┬─ibus-engine-sim
│ │ └─2*[{ibus-daemon}]
│ └─2*[{gnome-session-b}]
├─irqbalance
├─kerneloops
├─kube-proxy
├─kubelet
├─lightdm─┬─Xorg
│ └─lightdm───sh───fluxbox
├─lxcfs
├─lxd─┬─lxd
│ └─2*[{lxd}]
├─polkitd───2*[{polkitd}]
├─rsyslogd
├─snapd───10*[{snapd}]
├─ssh-agent
├─systemd-journal
├─systemd-logind
├─systemd-networkd
├─systemd-resolve
├─systemd-timesyn
├─systemd-udevd
├─udisksd───3*[{udisksd}]
├─unattended-upgr───2*[{unattended-upgr}]
├─upowerd───2*[{upowerd}]
├─user-manager───3*[{user-manager}]
└─whoopsie───2*[{whoopsie}]
This shows the user running each process.
The pstree command can be a valuable tool for understanding the process hierarchy on your Linux system. In the next step, we'll explore more ways to use pstree to gain insights into your system's processes.
