system-and-network-administration-course/week8/lab8-solution.org

#+title: Lab8 Solution
#+title: Amirlan Sharipov (BS21-CS-01)
#+author: Amirlan Sharipov (BS21-CS-01)
#+PROPERTY: header-args :results verbatim :exports both
#+OPTIONS: ^:nil

* Question 1
#+begin_src bash
systemd-analyze
systemd-analyze plot > systemd.svg
#+end_src

#+RESULTS:
: Startup finished in 5.093s (firmware) + 122ms (loader) + 7.459s (kernel) + 4.545s (userspace) = 17.221s
: graphical.target reached after 4.544s in userspace.

#+ATTR_HTML: :width 1000px
[[./systemd.svg]]

* Question 2
graphical.target -> multi-user.target -> basic.target -> sysinit.target

#+begin_src bash
cat /usr/lib/systemd/system/graphical.target
cat /usr/lib/systemd/system/multi-user.target
cat /usr/lib/systemd/system/basic.target
cat /usr/lib/systemd/system/sysinit.target
#+end_src

#+RESULTS:
#+begin_example
#  SPDX-License-Identifier: LGPL-2.1-or-later
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Graphical Interface
Documentation=man:systemd.special(7)
Requires=multi-user.target
Wants=display-manager.service
Conflicts=rescue.service rescue.target
After=multi-user.target rescue.service rescue.target display-manager.service
AllowIsolate=yes
#  SPDX-License-Identifier: LGPL-2.1-or-later
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Multi-User System
Documentation=man:systemd.special(7)
Requires=basic.target
Conflicts=rescue.service rescue.target
After=basic.target rescue.service rescue.target
AllowIsolate=yes
#  SPDX-License-Identifier: LGPL-2.1-or-later
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Basic System
Documentation=man:systemd.special(7)
Requires=sysinit.target
Wants=sockets.target timers.target paths.target slices.target
After=sysinit.target sockets.target paths.target slices.target tmp.mount

# We support /var, /tmp, /var/tmp, being on NFS, but we don't pull in
# remote-fs.target by default, hence pull them in explicitly here. Note that we
# require /var and /var/tmp, but only add a Wants= type dependency on /tmp, as
# we support that unit being masked, and this should not be considered an error.
RequiresMountsFor=/var /var/tmp
Wants=tmp.mount
#  SPDX-License-Identifier: LGPL-2.1-or-later
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=System Initialization
Documentation=man:systemd.special(7)

Wants=local-fs.target swap.target
After=local-fs.target swap.target
Conflicts=emergency.service emergency.target
Before=emergency.service emergency.target
#+end_example

** Information taken from man pages:
*** basic.target
A special target unit covering basic boot-up.
*** graphical.target
A special target unit for setting up a graphical login screen. This pulls in multi-user.target.
*** multi-user.target
A special target unit for setting up a multi-user system (non-graphical). This is pulled in by graphical.target.
*** sysinit.target
This target pulls in the services required for system initialization.
** Wants for sysinit.target
Wants=local-fs.target swap.target
Wants is used like Requires, but it's less strict, meaning that it can start if the "wanted" service doesn't exist or failed to start.
In this case, it wants local filesystems and swap to start.

* Question 3
#+begin_src bash
cat webserver.sh
#+end_src

#+RESULTS:
: #!/bin/bash
:
: while true ; do
:     STATS="<h1>Uptime</h1>$(uptime)\n<h1>Inode and disk usage</h1>$(df -ih)\n<h1>Mem usage</h1>$(free -h)\n<h1>Syslog</h1>$(tail -n 15 /var/log/syslog)\r\n\r\n"
:     LEN=$(printf "%s" "$STATS" | wc -c)
:     RES="HTTP/1.1 200OK\r\nContent-Length: $LEN\r\n\r\n"
:     echo -e "$RES$STATS"| nc -l -p 1500;
: done

[Unit]
Description=stats web server

[Service]
User=root
ExecStart=/home/rinri/edu/sna/webserver.sh
Restart=always
CPUQuota=15%
MemoryMax=256000000

[Install]
WantedBy=multi-user.target

* Question 4
#+begin_src bash
cat update.sh
#+end_src

[Unit]
Description=update package sources list

[Service]
User=root
ExecStart=/home/rinri/edu/sna/update.sh

[Install]
WantedBy=multi-user.target