At the beginning of the boot process, the kernel command line can be
edited by pressing the e
key as soon as
the Grub menu appears. In edit mode, use the arrow keys to navigate to
the kernel line and insert the desired cheatcode(s) at the end. The
space character serves as separator. To conitnue the boot process, enter
Ctrl
+X
.
The following links lead to the manual page with the tables for the boot options.
Detailed reference list for kernel bootcodes from kernel.org
systemd knows a total of 11 unit types. The units we deal with most often in everyday life are:
We briefly introduce some of the unit types here. Their names already
give an indication of their intended functionality. More detailed
explanations of the units can be found on our manual page System
administration - systemd. The complete documentation can be found in
the man pages man systemd.unit
,
man systemd.special
, and
man systemd.<unit_type>
respectively.
The systemd system can be controlled with follwing command, which requires user or root rights depending on the units:
systemctl [OPTIONS...] command [UNIT...]
systemctl
knows autocompletion by
TAB
and the display of all variations by
TAB
TAB
.
Please read the man page man systemctl
.
A list sorted by types with all active units or unit files can be output with the following commands:
$ systemctl list-units # for units
$ systemctl list-unit-files # for unit files
With the -a
option all inactive units or unit files are
also output.
To start or stop a .service unit, use the commands:
$ systemctl start <UNIT>.service
$ systemctl stop <UNIT>.service
$ systemctl restart <UNIT>.service
“Restart” is useful, for example, to notify the service of a
changed configuration. If root privileges are required
for the action, the root password is requested.
The command can also be used to terminate a service:
$ systemctl kill -s SIGSTOP --kill-who=control <UNIT>.service
With “kill”, in contrast to “stop”, the options
-s
, --signal=
, and --kill-who=
are available.
SIGTERM
,
SIGINT
, or SIGSTOP
. Default is
“SIGTERM”.main
, control
, or all
. This sends
the signal to the main process, the child processes, or both. Default is
“all”.This behavior is similar to the old and still usable command pkill, which is explained below in the section Terminating a process.
To have a (self-made) unit loaded automatically when the computer is booted, enter as root:
# systemctl enable <UNIT_file>
This creates a group of symlinks according to the requirements in the unit’s configuration. Following this, the system manager configuration is automatically reloaded.
The command
# systemctl disable <UNIT_file>
removes the symlinks again.
Example
If a PC or laptop without Bluetooth hardware is in use, or you don’t
want to use Bluetooth, the command (as root)
# systemctl disable bluetooth.service
will remove the symlinks from all requirements and dependencies within systemd and the service will no longer be available and will not be started automatically.
Already since the 2013.2 “December” release, siduction has been using
systemd as the default init system.
The old sysvinit commands are still supported. (for this a quote from
man systemd
: “… is provided for compatibility reasons and
because it is easier to type.”)
More detailed information about systemd can be found on the manual page
System
administration - systemd.
The various runlevels that are booted or switched to are described by
systemd as target units. They have the extension
.target.
Target Unit | Description |
---|---|
emergency.target | starts into an emergency shell on the main console. It is the minimum version of a system boot to obtain an interactive shell. This unit can be used to guide the boot process step by step. |
rescue.target | starts the base system (including system mounts) and an emergency shell. Compared to multi-user.target, this target could be considered as single-user.target. |
multi-user.target | starts a multi-user system with a working network, without graphics server X. This unit is used when you want to stop X or to not boot into X. A system update (dist-upgrade) is performed on this unit . |
graphical.target | starts multi-user mode with network capability and a running X Window System. |
default.target | is the default unit that systemd starts at system startup. In siduction this is a symlink to graphical.target (except NoX). |
A look into the documentation
man SYSTEMD.SPECIAL(7)
is mandatory to
understand the relationships of the different “.target -
units”.
To switch to the system update runlevel, use the following command as root in the terminal:
# systemctl isolate multi-user.target
Important here is the “isolate” command, which ensures the termination of all processes and services that the selected unit does not request.
To shut down or restart the system, the command
# systemctl poweroff
or
# systemctl reboot
can be used. “poweroff” or “reboot” (each without .target) are commands that starts several units in the correct order to terminate the system in an orderly fashion and to reboot if necessary.
pgrep and pkill
Independently of systemd, pgrep
and pkill
are a very useful duo to terminate unwelcome processes. Run with
user or root privileges in a console
or TTY:
$ pgreg <tab> <tab>
The command lists all processes with their name, but without the
process ID (PID). We use Firefox as an example in the following.
The -l
option prints the PID and the full name:
$ pgrep -l firefox
4279 firefox-esr
To display subprocesses, if any, we also use the -P
option and only the PID:
$ pgrep -l -P 4279
4387 WebExtensions
4455 file:// Content
231999 Web Content
then
$ pkill firefox-esr
terminates Firefox with the default signal SIGTERM.
With the option –signal, followed by the signal number
or the signal name, pkill sends the desired signal to the
process. A clear list of signals can be obtained with kill
-L.
htop
Entered in the terminal, htop is a good alternative because a lot of useful information about the processes and the system load is presented. This includes a tree view, filter and search function, kill signal, and some more. The operation is self-explanatory.
Emergency exit
As a last resort before pulling the power plug, you can use the
command killall -9
in the terminal.
A forgotten root password cannot be recovered, but a new one can be set.
To do this, the live CD must first be booted.
The root partition must be mounted as root (e.g. as /dev/sdb2)
mount /dev/sdb2 /media/sdb2
Now enter the root partition with chroot (chroot = changed root) and define a new password:
chroot /media/sdb2 passwd
To change a user password, as user :
$ passwd
To change the root password, as root :
# passwd
To change a user password as administrator, as root :
# passwd <user>
To improve the display of fonts, if necessary, it is important to check the correct settings and configurations of the hardware beforehand.
Check settings
Correct graphics drivers
Some newer ATI and Nvidia graphics cards do not harmonize very well with
the free Xorg drivers. The only reasonable solution in these cases is to
install proprietary, non open source drivers. For legal reasons,
siduction cannot pre-install these. Instructions for installing these
drivers can be found on the Graphics Drivers page of the
manual.
Correct screen resolutions and refresh
rates.
First, it’s a good idea to look at the manufacturer’s technical
documentation, either in print or online. Each monitor has its own
perfect combination of settings. These DCC values are usually passed
correctly to the operating system. Only sometimes it is necessary to
intervene manually to overwrite the basic settings.
To check which settings the X server is currently using, we use xrandr in the terminal:
$ xrandr
Screen 0: minimum 320 x 200, current 1680 x 1050,
maximum 16384 x 16384
HDMI-1 disconnected
(normal left inverted right x axis y axis)
HDMI-2 connected 1680x1050+0+0 (normal left
inverted right x axis y axis) 474mm x 296mm
1680x1050 59.95*+
1280x1024 75.02 60.02
1440x900 59.90
1024x768 75.03 60.00
800x600 75.00 60.32
640x480 75.00 59.94
720x400 70.08
DP-1 disconnected
(normal left inverted right x axis y axis)
The value marked with “*” indicates the setting used,
1680 x 1050 pixels with a physical size of 474 x 296 mm. In addition, we
calculate the actual resolution in px/inch (dpi) to get an indication of
the settings for the fonts. With the values given above we get 90
dpi.
1680 Px x
25,4 mm/inch /
474 mm =
90 Px/inch (dpi)
Check
We use a folding rule or tape measure to determine the actual size of
the monitor. The result should differ by less than three millimeters
from the values output by xrandr.
Basic font configuration
siduction uses free fonts that have proven to be balanced in Debian. In the graphical user interface TTF or outline fonts are used. If own fonts are chosen, new configuration adjustments may have to be made to get the desired font appearance.
The system-wide basic configuration is done in the terminal as root, using:
# dpkg-reconfigure fontconfig-config
For the dialogs called, these settings have proven to be useful:
medium
automatic
no
Subsequently
# dpkg-reconfigure fontconfig
is necessary to rewrite the configuration.
Sometimes rebuilding the font cache is a solution (the first command is for saving data with a date appendix, the second command is to be entered without a line break, i.e. on one line):
# mv /etc/fonts/ /etc/fonts_$(date +%F)/
# apt-get install --reinstall --yes -o DPkg::Options::=
--force-confmiss -o DPkg::Options::=--force-confnew
fontconfig fontconfig-config
Display type, size, 4K display
It should be noted that each font has an ideal size range, so
identical size settings do not necessarily lead to the same good result
for each font.
The settings can be made conveniently in the graphical interface. They
take effect on the desktop immediately, applications have to be
restarted to some extent.
The list shows where in the menu the settings can be found.
KDE Plasma
Gnome (Tweak Tool)
“Applications” > “Optimizations” >
“Fonts”
Xfce
“Preferences” > “Appearance” > tab:
“Fonts”
Explanation of terms
“Edge smoothing / Antialising”:
This is the brightness gradation of the neighboring pixels at the edges
to reduce the staircase effect on curves. However, it causes some
blurring of the characters.
“Subpixel rendering / color order / RGB”:
This is an extension of antialising for LCD screens by additionally
controlling the color components of a pixel.
“Hinting”:
This is the adaptation (change) of the characters to the pixel grid of
the screen. It reduces the need for antialiasing, but the font shape no
longer conforms exactly to the specifications, unless the font
developers have already incorporated hinting variations. For
4K screens, hinting is usually not necessary.
“DPI value / scaling factor”:
This setting allows a different DPI value or size for the fonts only.
Here the display on a 4K screen can be improved
quickly. The following table illustrates the relationship between screen
diagonal and DPI value for 4K screens.
4K resolution: 3840 x 2160 (16:9)
Diagonal | X-axis | Y-axis | DPI |
---|---|---|---|
24 inch | 531 mm | 299 mm | 184 |
27 inch | 598 mm | 336 mm | 163 |
28 inch | 620 mm | 349 mm | 157 |
32 inch | 708 mm | 398 mm | 138 |
37 inch | 819 mm | 461 mm | 119 |
42 inch | 930 mm | 523 mm | 105 |
Accordingly, a scaling factor of 2.0 is required for 4k screens with a diagonal of 24 inches, and a scaling factor of 1.2 is required for screens with a diagonal of 37 inches in order to obtain approximately equal displays corresponding to SXGA or WSXGA screens with 90 DPI.
KDE has a large section on CUPS in the KDE help. Nevertheless, here is a guide on what to do if you have problems with CUPS after a full-upgrade. One of the known solutions is:
# modprobe lp
# echo lp >> /etc/modules
# apt purge cups
# apt install cups
OR
# apt install cups printer-driver-gutenprint hplip
CUPS will now be restarted:
# systemctl restart cups.service
Afterwards open a web browser and type this into the address line:
http://localhost:631
A small problem occurs when CUPS opens the corresponding dialog box for legitimation. Occasionally, the user’s own user name is already entered there and the password is expected. However, entering the user password does not work. Nothing works. The solution is to change the user name to root and enter the root password.
The OpenPrinting database contains extensive information about various printers and their drivers. Drivers, specifications, and configuration tools are available. Samsung used to supply its own Linux drivers for its printers. After the printer division had been sold to HP, the download page has no longer been available, and HP unfortunately did not include the Samsung drivers in “hplib”. Currently, the package printer-driver-splix works best for Samsung printers and Samsung multifunction devices. CUPS is currently in transition and is moving towards printing without drivers via PWG - IPP Everywhere, see also debian - an introduction to IPP-Everywhere.
In older siduction installations, sound is disabled by default.
Most sound problems can be solved by clicking on the sound icon in the control bar, opening the mixer, and unchecking “mute”, or using the appropriate slider. If the speaker icon is not present, a right click on the control bar is sufficient, then select
in KDE: “Control Panel Options” > “Add Mini
Programs…”
in Xfce: “Bar” > “Add new items…”
and select the desired module.
KDE Plasma
A right click on the speaker icon in the control bar opens the sound output settings window. The user interface is self-explanatory.
Gnome
Right-clicking on the speaker icon in the control bar opens a
drop-down menu that contains a slider for the volume.
Further settings are possible as follows:
Right-click on the desktop > “Settings” > “Audio”
Xfce Pulse Audio
The settings are made via the speaker icon (pulse audio module) in the control bar. Again, the user guidance is self-explanatory. If the icon is missing, you can quickly get started with a terminal by entering the command
$ pavucontrol
and configuring the settings in the appearing window.
Alsamixer
If you prefer alsamixer, you can find it in the alsa-utils package:
# apt update
# apt install alsa-utils
# exit
The desired sound settings are made as user from a terminal:
$ alsamixer