Linux

1. Razer Blade Stealth in Linux
2. LAMPP local server
3. Git basics
4. Bash
5. sed

#print user PATH
$ printenv PATH
/bin:/sbin:/usr/bin:/usr/sbin
$ echo "$PATH"
/bin:/sbin:/usr/bin:/usr/sbin
 
#How it works
$ ping 127.0.0.1
 
    PATH=/bin:/sbin:/usr/bin:/usr/sbin
           │     │
           │     ╰──▶ /sbin/ping ?  found!
           ╰──▶ /bin/ping ?  not found.
 
#Add a folder to path for current shell session
$ PATH=$PATH:/path/to/app/folder

There is debate as to where binaries that you install yourself should be put in the filesystem. The proper places to put them seem to be :

/opt/ <- for bundled applications, typically grabbed from a software developper
/usr/local/ <- for applications built by the administrator for local use, i.e. using "make" or other
/home/USER/opt/ <- for single-user use only

FHS Reference

Include the following line in /home/USER/.profile :

EXPORT PATH="/path/to/bin/folder:$PATH"

This will only be active after logging out. If you want to activate it without logging out for a current shell session run the following command :

$ source /home/USER/.profile

Note that the path must point to the folder containing the binary and not to the binary itself.

Cinnammon has implemented a handy GUI Editor you can access by right-clicking the 'Menu' icon and selecting 'configure'. You can also launch :

$ cinnamon-menu-editor

Using bash you can create a symbolic link to a .desktop file anywhere on your system and place that link in /usr/share/applications

$ ln -s path/to/target/file.desktop LINK_NAME

Make sure the .desktop file has proper permissions :

$ chmod 644 path/to/file.desktop 

The menu entry will appear after logging out.

$ type man
man is /usr/bin/man

Extract the content of an AppImage :

./your.AppImage –appimage-extract

This is useful if you want to get the Icon.

Link to AppImage Daemon This Daemon scans well known places for appimages and creates menu entries and extracts icons

Config file is located at /etc/default/grub

The line for a splash image is GRUB_BACKGROUND=/path/to/image.jpg

There are various ways to limit the CPU usage of a process. One simple way is using cpulimit

$ cpulimit -P /path/to/executable -l %CPU (e.g. 40) -b (background)

Ressource site

To quickly install folders containing many OpenType fonts (OTF) or TrueType fonts (TTF), copy to the following locations :

$ sudo cp -r /path/to/OTF-folder /usr/share/fonts/opentype/
$ sudo cp -r /path/to/TTF-folder /usr/share/fonts/truetype/

Regenerate font cache :

$ sudo fc-cache -f -v

Note : This will install fonts system-wide. To install for a single user only copy the files to :

~/.fonts/

and regenerate font cache.

Use (pdftk (ubuntu) → deprecated) or pdf-stapler (fedora) :

For example to extract two pages out of a pdf

$ pdf-stapler cat in.pdf 2-3 out.pdf

Old syntax with pdftk : $ pdftk in.pdf cat 3-4 output out.pdf

pdfshuffler is a front end for python-pyPdf and a great tool for merging or splitting pdf files with a GUI.

Found from this answer on AskUbuntu :

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

-dPDFSETTINGS can be the following :

• /screen lower quality, smaller size. (72 dpi)
• /ebook for better quality, but slightly larger pdfs. (150 dpi) - This one gives quite a good ratio of quality-loss/size-reduction
• /prepress output similar to Acrobat Distiller “Prepress Optimized” setting (300 dpi)
• /printer selects output similar to the Acrobat Distiller “Print Optimized” setting (300 dpi)
• /default selects output intended to be useful across a wide variety of uses, possibly at the expense of a larger output file

When FAT32 filesystems mount in read-only it's often related to corrupted filesystem.

Run dmesg to check. If you see lines such as :

[54259.098330] FAT-fs (sdb1): error, corrupted directory (invalid entries)
[54259.098338] FAT-fs (sdb1): Filesystem has been set read-only
[54304.610623] FAT-fs (sdb1): error, corrupted directory (invalid entries)
[54304.690012] FAT-fs (sdb1): error, invalid access to FAT (entry 0xf7d0f91e)
[54304.690213] FAT-fs (sdb1): error, invalid access to FAT (entry 0xff27ff23)
[54304.690314] FAT-fs (sdb1): error, invalid access to FAT (entry 0xff0dff13)

Run the following command :

$ sudo umount /dev/sdX#
$ sudo fsck.msdos -aw /dev/sdX#

Stack Exchange thread on the subject

Try Test Disk & PhotoRec written by Christophe Grenier

PhotoRec 7.1-WIP In FileOptsMenu check :

[X] mov/mdat Recover mdat atom as a separate file

Two files are created for every .mov recovered. Concatenate with :

cat f123_ftyp.mov f456_mdat.mov > 1.mov
cat f456_mdat.mov f123_ftyp.mov > 2.mov

One of the two files will be good. Sometimes one file is .mp4 and the other is .mov :

cat f54114560.mp4 f51781632_mdat.mov > 1.mov

If a NTFS volume mounts in read-only, remount using :

$ su
$ mkdir /mnt/ntfs
$ mount -t ntfs /dev/sd[X] /mnt/ntfs

• /etc/mplayer/mplayer.conf

• ~/.mplayer/config
• ~/.mplayer/input.conf
• ~/.mplayer/menu.conf

fs=yes #enable fullscreen
noborder=yes
ontop=yes
geometry=+3200
osdlevel=0

sg3-utils

(usually sr0 or sr1)

$ ls /dev | grep 'dvd'

(change sr0 accordingly if needed)

$ sg_raw /dev/sr0 EA 00 00 00 00 00 01

This is not specifically linux-related but since every time I install it (especially on MacOS systems) it's such a pain to find the plugins/ folder from where to remove the plugins blocking the trial version of QCAD here's an easy way to find them :

Go to Help > About > Plugins and just click on the name of one of the plugins.

In MacOS it will be QCAD > About > Plugins instead.

Start stop the server using :

sudo /opt/lampp/lampp start/stop

Put your sites and data in :

/opt/lampp/htdocs/example_site

Identify your wired interface card module. Realtek 8169 is known to have this issue with some kernels.

$ lsmod

Look for :

....
hid                   118784  2 usbhid,hid_generic
ahci                   36864  4
r8169                  86016  0
libahci                32768  1 ahci
mii                    16384  1 r8169
...

Edit (create if it doesn't exist) the file :

$nano /etc/pm/config.d/unload_modules

Append the following line :

SUSPEND_MODULES="$SUSPEND_MODULES r8169"

Replace module name if necessary

Note to self : Added “mii” module to the list, the fix didn't seem to hold after reboot. Mii seems to be using r8169 and is network-monitoring-related

If following error occurs while using youtube-dl :

/usr/bin/env: ‘python’: No such file or directory

$sudo apt install python3

$whereis python3
$sudo ln -s /usr/bin/python3 /usr/bin/python

Change first argument according to where python3 is installed.

• Kazam : only one tried at the moment, produces OK files and you can select a specific region you want to capture
• gtk-recordmydesktop
• vokoscreen
• simplescreenrecorder
  • add-apt-repository ppa:maarten-baert/simplescreenrecorder

This requires a valid .ovpn file

openvpn --config /path/to/file.ovpn

Linux.com OpenVPN connection tutorial

This requires the ip of the shared folders location

Replace host with the hostname or IP address of the server running samba shares

$ smbclient -L host

Output will be something like this

	Sharename       Type      Comment
	---------       ----      -------
	home            Disk      
	shares          Disk      
	users           Disk      
	IPC$            IPC       IPC Service ()

Reconnecting with SMB1 for workgroup listing.

	Server               Comment
	---------            -------

	Workgroup            Master
	---------            -------
	MY_WORK              CODE-CA04

More ressources here

Most of the time they are located at /run/user/##ID##/gvfs

Create an alias using command

alias name='command'

The alias is only in place while the user session is active. To make it permanent, write it in the .bashrc file in the home directory of the user. (more info)

You can reload the .bashrc file using :

$ source ~/.bashrc
#or
$ . ~/.bashrc

$ sudo apt install xbindkeys xvkbd
$ xev | grep ', button' #Find the buttons you need to map
$ touch ~/.xbindkeysrc
$ nano ~/.xbindkeysrc

Sample File :

# Send enter on thumb mouse button
"xvkbd -text '\r'"
b:8

Ccheck xvkbd for more syntax

Debian Admin guide to mass renaming You can use for commands in the shell or use the 'rename' tool (written in perl). For example :

skx@lappy:~$ ls
a.JPG  b.JPG  c.JPG  d.JPG
skx@lappy:~$ for i in *.JPG; do mv "$i" "${i/.JPG}"; done
skx@lappy:~$ ls
a.jpg  b.jpg  c.jpg  d.jpg

Remove sections from input and output them

$ date
Thu 02 Jan 2020 08:20:10 PM CET
$ date | cut -c17-24
08:21:02

List mounts

$ findmnt

Target disk

$ sudo fdisk -l
Disk /dev/sda
[...]
Disk /dev/sdb
[...]

Create mount point

$ sudo mkdir /media/DRIVE

Mount device

$ sudo mount /dev/sda1 /media/DRIVE

Unmount

$ sudo umount /media/DRIVE

More info

Display Present Working Directory

$ pwd
/home/pi

Pack/Unpack tarball

#All the following commands are verbose (-v) and target a file archive (-f)
$ tar -xvf file.tar #Unpack tar (-x : extract)
$ tar -xvzf file.tar.gz #Unpack compressed (gzip) tar (-z : filter through gzip)
$ tar -cvf file.tar /path/folder #Pack folder into file.tar archive (-c : create)
$ tar -cvzf file.tar /path/folder #Same as above with compression (gzip) (-z : filter through gzip)

Extensive Guide

sudo service smbd start/stop/restart

This can fix some states in which apt is broken and refuses to update because some libraries fail :

$ dpkg --configure -a
$ apt --fix-broken install

$ inxi -F

Read the manual, inxi is a very powerful tool to quickly get an overview of a full hardware setup

$ lsb_release -d

Basic

$ lscpu

Detailed, core-specific information, output /proc/cpuinfo

$ cat /proc/cpuinfo

On Macs :

$ sysctl -n machdep.cpu.brand_string

$ df -h

$ uname -snrm

• s : kernel name
• n : network node hostname
• r : kernel relase number
• m : machine hardware name

http://www.tecmint.com/useful-linux-commands-for-system-administrators/

$ lsmod

$ history

$ gdbus
$ g-feet //gui history

$ sudo dmidecode | grep -A3 ‘^System Information’

dmidecode spurns out a lot of information if you want to query your system

$ uptime [load Average]
$ dmesg -T | tail [Kernel errors]
$ vmstat 1 [Virtual memory and detailed information]
$ mpstat -P ALL 1 [CPU state]
$ pidstat [processes]
$ free -m [memory]
$ atop [main overview]

/var/log/syslog

Check in /var/log which file was last changed. Use :

$ls -lart //inverted sorted by time. Last entry is latest modified

• SysRq Keys – Best combo is Alt + SysRq + R E I S U B

• Advanced Linux Troubleshooting

• Creating GPT/exFAT partitions using CLI