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A collection of notes on using Linux systems.
A collection of notes on using Linux systems.
Notes here are for Ubuntu but should work on similar debian derivative distros.
Notes here are for Ubuntu but should work on similar debian derivative distros.
See also [[NixOS]].


==Basic Terminal Commands==
{{see also | Bash (Unix shell)}}
===List===
<code>ls</code>
* <code>-l</code> shows long format
* <code>-a</code> shows all files including hidden files, current directory <code>.</code>, and parent directory <code>..</code>.
** <code>-A</code> omits <code>.</code> and <code>..</code>
* <code>-h</code> human readable file sizes
* <code>-s</code> shows blocks taken up by the file (i.e. size on disk)


==Basic Terminal Commands==
There are also other commands like <code>lsblk</code>, <code>lscpu</code>, <code>lshw</code>.


===Disk Space===
===Disk Space===
* <code>du</code> Disk Usage
* <code>du</code> Disk Usage
** <code>du -sh</code> Show size of current directory
** <code>du -sh</code> Show size of current directory
** <code>du -h --max-depth=1</code>
** <code>du -h --max-depth=1</code> Show size of files and folders in current directory. I have <code>du</code> aliased to this.
** Flags:
** Flags:
*** <code>-h</code> human readable (adds M or G)
*** <code>-h</code> human readable (adds M or G)
*** <code>--max-depth</code> depth to recurse. Default is <code>N</code>.
* <code>df</code> Disk Filesystems
* <code>df</code> Disk Filesystems
** Shows usage, total space available, and mount position
** Shows usage, total space available, and mount position
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* <code>2>&1</code> will redirect stderr (2) to stdout (1)
* <code>2>&1</code> will redirect stderr (2) to stdout (1)
* [https://www.gnu.org/software/coreutils/manual/html_node/tee-invocation.html <code>tee</code>] will redirect stdout to multiple files and show it in the terminal
* [https://www.gnu.org/software/coreutils/manual/html_node/tee-invocation.html <code>tee</code>] will redirect stdout to multiple files and show it in the terminal
===Shutdown===
<pre>
shutdown -h [now | -t <time>]
</pre>
* <code>-h</code> poweroff, the default
* <code>-t time</code> schedule a shutdown in ''time'' seconds
* <code>-r</code> restart
* <code>-c</code> cancel pending shutdown


==Package Management==
==Package Management==
See [https://www.digitalocean.com/community/tutorials/package-management-basics-apt-yum-dnf-pkg DigitalOcean: Package management basics]
===apt===
===apt===
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
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</syntaxhighlight>
</syntaxhighlight>


===Repositories===
;Repositories
Repos are stored in
Repository sources are saved in
* <code>/etc/apt/sources.list</code>
* A line in <code>/etc/apt/sources.list</code>
* A file in <code>/etc/apt/sources.list.d/</code>
* A file in <code>/etc/apt/sources.list.d/</code>


Application desktop icons are stored in <code>/usr/share/applications/</code>.
The update notifications are in <code>/etc/apt/apt.conf.d/99update-notifier</code>. Comment these out to disable them.<br>
Unattended-updates are in <code>/etc/apt/apt.conf.d/50unattended-upgrades</code>.
{{hidden | dpkg |
===dpkg===
===dpkg===
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
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sudo dpkg -l | grep apache
sudo dpkg -l | grep apache
</syntaxhighlight>
</syntaxhighlight>
}}
{{hidden | yum |
===yum===
<syntaxhighlight lang="bash">
# Update package lists, typically not necessary
yum check-update
# Upgrade packages
yum update
</syntaxhighlight>
}}


==SSH==
==SSH==
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Generate an ssh-key for every client
Generate an ssh-key for every client
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
ssh-keygen -t ed25519 -a 100 [-C "comment your client name"] [-f output_path]
ssh-keygen -t ed25519 [-C "comment your client name"] [-f output_path]
</syntaxhighlight>
</syntaxhighlight>


Some older software such as Solid file explorer require RSA keys in PEM key format
Some older software such as Solid file explorer require RSA keys in PEM key format
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
ssh-keygen -t rsa -b 4096 -a 100 -m PEM [-C "comment your client name"] [-f output_path]
ssh-keygen -t rsa -b 4096 -m PEM [-C "comment your client name"] [-f output_path]
</syntaxhighlight>
</syntaxhighlight>


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===Disable password authentication===
===Disable password authentication===
* Edit <code>/etc/ssh/sshd_config</code>
# Edit <code>/etc/ssh/sshd_config</code>
* Set <code>PasswordAuthentication</code> to <code>no</code>
# Set <code>PasswordAuthentication</code> to <code>no</code>
* Set <code>ChallengeResponseAuthentication</code> to <code>no</code>
# Set <code>ChallengeResponseAuthentication</code> to <code>no</code>
# Test by ssh'ing into the machine using <code>-o PreferredAuthentications=password -o PubkeyAuthentication=no</code>


===Port Forwarding===
===Port Forwarding===
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===Driver Installation===
===Driver Installation===
* Run <code>ubuntu-drivers list</code> to get a list of drivers
# Run <code>ubuntu-drivers list</code> to get a list of drivers
* Install the latest driver
# Install the latest driver
** E.g. <code>sudo apt install nvidia-driver-440</code>
#* E.g. <code>sudo apt install nvidia-driver-460</code>
* If you have secure boot enabled, you will be asked for a password during installation
# If you have secure boot enabled, you will be asked for a password during installation
** This is because the driver is a DKMS module.
#* This is because the driver is a DKMS module.
** After installation, reboot your computer and select "Enroll MOK" and enter that password in.
#* After installation, reboot your computer and select "Enroll MOK" and enter that password in.
** '''Note''' Failure to do this will result in the driver not working
#* '''Note''' Failure to do this will result in the driver not working
* Validate your installation by running <code>nvidia-smi</code>
# Validate your installation by running <code>nvidia-smi</code>.
#* <code>nvidia-smi</code> shows the latest cuda version supported by the driver, not the cuda version installed.


===Cuda Installation===
===Cuda Installation===
Download cuda from the nvidia website.
Download cuda from the nvidia website or add the cuda repo to your apt sources.


===Switching between Nvidia and Intel===
===Switching between Nvidia and Intel===
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</pre>
</pre>
<code>prime-select query</code> will print either <code>nvidia</code> or <code>intel</code> to stdout.
<code>prime-select query</code> will print either <code>nvidia</code> or <code>intel</code> to stdout.
===Fix tearing on laptops===
[https://ubuntuhandbook.org/index.php/2018/07/fix-screen-tearing-ubuntu-18-04-optimus-laptops/ Reference]<br>
# Add <code>options nvidia-drm modeset=1</code> to <code>/etc/modprobe.d/nvidia-drm-nomodeset.conf</code>
# Run <code>sudo update-initramfs -u</code>


==Environment Variables==
==Environment Variables==
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# Attach to a session
# Attach to a session
tmux attach -t my_session
tmux attach -t my_session
# Renumber windows
:movew
</syntaxhighlight>
</syntaxhighlight>
===Mouse scrolling===
Set <code>set -g mouse on</code> in your <code>~/.tmux.conf</code>


==File Manager==
==File Manager==
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===Add to context menu===
===Add to context menu===
[https://askubuntu.com/questions/1030940/nautilus-actions-in-18-04 Link]
[https://askubuntu.com/questions/1030940/nautilus-actions-in-18-04 AskUbuntu]


;19.04+
;22.04
See [https://github.com/harry-cpp/code-nautilus https://github.com/harry-cpp/code-nautilus]
 
;20.04
<pre>
<pre>
sudo add-apt-repository universe
sudo add-apt-repository universe
sudo apt-get install filemanager-actions
sudo apt update
sudo apt update
sudo apt install filemanager-actions nautilus-actions nautilus-extension-fma
</pre>
</pre>
;18.04
<pre>
</pre>
To add Atom, create two entries: 
;Open file in Atom and Open folder in Atom
<pre>
Path: atom
Parameters: %f
Working directory: %d
</pre>
You may also want:
;Copy folder path and Copy file path


==Etcher==
==Etcher==
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===Docker===
===Docker===
{{main | Docker}}
{{main | Docker (software)}}


==Services and Scheduling==
==Services and Scheduling==
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===systemd service===
===systemd service===
See [https://wiki.debian.org/systemd/Services] [https://www.freedesktop.org/software/systemd/man/systemd.service.html manual]<br>
See [https://wiki.debian.org/systemd/Services debian/systemd Services]<br>
[https://www.freedesktop.org/software/systemd/man/systemd.service.html manual]<br>
 
System-wide services are in <code>/etc/systemd/system/</code><br>
User services are in <code>~/.config/systemd/user/</code>
 
{{hidden|A basic systemd service file|
{{hidden|A basic systemd service file|
<pre>
<pre>
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# Archive
# Archive
7z a <output_file> <input_file/folder>
7z a <output_file> <input_file/folder>
# Archive with password
7z a <output_file> <input_file> -p -mhe=on


# Extract  
# Extract  
7z x <file> [-o{dir}]
7z x <file> [-o{dir}]
</syntaxhighlight>
</syntaxhighlight>
* <code>-mhe=on</code> hides file stuctures


===zip/unzip===
===zip/unzip===
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===tar===
===tar===
{{ main | tar (computing) }}
;Extraction
;Extraction
<pre>
<pre>
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tar czpvf archive.tar.gz files
tar czpvf archive.tar.gz files
</pre>
</pre>
;Flags
* <code>-x</code> extract preserving paths
* <code>-p</code> preserve permissions
* <code>-c</code> create an archive
* <code>-f</code> specify file
;Compression formats
* <code>-z</code> use gzip
* <code>-j</code> use bzip2
* <code>-J</code> use xz


===find===
===find===
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==Dual Booting==
==Dual Booting==
===Fix time difference between Windows===
===Fix time difference between Windows===
[http://ubuntuhandbook.org/index.php/2016/05/time-differences-ubuntu-1604-windows-10/ Reference]
By default, Windows stores the local time in the hardware clock while Ubuntu stores UTC time.
 
Set ubuntu to store UTC time:
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
timedatectl set-local-rtc 1 --adjust-system-clock
timedatectl set-local-rtc 0 --adjust-system-clock
</syntaxhighlight>
</syntaxhighlight>
Set Windows to store UTC time:
https://wiki.archlinux.org/title/System_time#UTC_in_Microsoft_Windows


===Recover GRUB after installing Windows===
===Recover GRUB after installing Windows===
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Allows you to reboot into an OS one time.<br>
Allows you to reboot into an OS one time.<br>
i.e. If you are ssh'd into linux and want to boot into Windows one time.<br>
i.e. If you are ssh'd into linux and want to boot into Windows one time.<br>
===Encryption===
[https://www.mikekasberg.com/blog/2020/04/08/dual-boot-ubuntu-and-windows-with-encryption.html https://www.mikekasberg.com/blog/2020/04/08/dual-boot-ubuntu-and-windows-with-encryption.html]


==Users and Groups==
==Users and Groups==
===Users===
<syntaxhighlight lang="bash">
# Make a new user
adduser <user>
# Add user to admins
usermod -aG sudo <user>
# Change the password of a user
passwd
passwd <user>
# Delete a user
# -r will also delete their home directory
userdel -r <user>
</syntaxhighlight>
===Groups===
===Groups===
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
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# Add user to group
# Add user to group
usermod -a -G <group> <user>
usermod -a -G <group> <user>
# Remove user from group
gpasswd -d <user> <group>
</syntaxhighlight>
</syntaxhighlight>


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===chmod===
===chmod===
change mode
===chown===
===chown===
change owner
<pre>
chown [-r] <user>[:<group>] <item>
</pre>
===chgrp===
===chgrp===


==Display Scaling==
===Access Control Lists (ACL)===
See [https://wiki.archlinux.org/index.php/HiDPI Arch Wiki HiDPI]
 
==Display Scaling (HiDPI)==
See [https://wiki.archlinux.org/index.php/HiDPI Arch Wiki HiDPI]
 
Fractional scaling is natively available in Ubuntu 20.04+.


{{hidden | Ubuntu 18.04 |
;Xorg
;Xorg
<pre>
<pre>
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xrandr --output DP-2 --scale 1.3x1.3
xrandr --output DP-2 --scale 1.3x1.3
</pre>
</pre>
}}


==Clock==
==Clock==
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==<code>/dev/</code>==
==<code>/dev/</code>==
See [[Wikipedia: Device file#Pseudo-devices]]
===<code>null</code>===
Discards all input. 
Produces EOF.
===<code>random</code>===
===<code>random</code>===
See [https://security.stackexchange.com/questions/3936/is-a-rand-from-dev-urandom-secure-for-a-login-key/3939#3939 stackexchange]<br>
See [https://security.stackexchange.com/questions/3936/is-a-rand-from-dev-urandom-secure-for-a-login-key/3939#3939 stackexchange]<br>
Line 534: Line 620:


;TLDR&#58; Use <code>/dev/urandom</code> instead of <code>/dev/random</code>
;TLDR&#58; Use <code>/dev/urandom</code> instead of <code>/dev/random</code>
===<code>urandom</code>===
Produces random numbers.
On my system, it's limited to about 60 MB/s. If you need faster randomness, you can encrypt from <code>/dev/zero</code> to get 2.7 GB/s. 
See [https://serverfault.com/questions/6440/is-there-an-alternative-to-dev-urandom/415962#415962 reference].
<pre>
# Using urandom
pv < /dev/urandom > /dev/ull
# Using encryption
openssl enc -pbkdf2 -iter 100000 -aes-256-ctr -pass pass:"$(dd if=/dev/urandom bs=128 count=1 2>/dev/null | base64)" -nosalt < /dev/zero | pv > /dev/null
# Create a 4 GB file.
dd if=/dev/zero bs=4M count=1024 | openssl enc -pbkdf2 -iter 100000 -aes-256-ctr -pass pass:"$(dd if=/dev/urandom bs=128 count=1 2>/dev/null | base64)" -nosalt | pv > random.bin
</pre>


==Gnome==
==Gnome==
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[https://unix.stackexchange.com/questions/141095/automatically-reboot-if-no-wifi-connection-for-a-certain-time reference]
[https://unix.stackexchange.com/questions/141095/automatically-reboot-if-no-wifi-connection-for-a-certain-time reference]


{{hidden | Auto Reboot Script |
Auto reboot if no internet is detected:
Auto reboot if no internet is detected:
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
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*/10 * * * * /home/david/bin/check_inet.sh
*/10 * * * * /home/david/bin/check_inet.sh
</pre>
</pre>
}}


==Encryption==
==Encryption==
For encrypting external drives, I recommend [[VeraCrypt]].
For encrypting entire drives, I recommend LUKS.<br>
I do not recommend using Ubuntu's full disk encryption. 
If you want encrypt a directly, you can use fscrypt (ext4 only).
If you want to do encryption, just encrypt your home directory using fscrypt.
 
Note that ecryptfs is deprecated and shouldn't be used.


===Encrypt Home After Install===
===Encrypt Home After Install===
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See [https://tlbdk.github.io/ubuntu/2018/10/22/fscrypt.html https://tlbdk.github.io/ubuntu/2018/10/22/fscrypt.html].
See [https://tlbdk.github.io/ubuntu/2018/10/22/fscrypt.html https://tlbdk.github.io/ubuntu/2018/10/22/fscrypt.html].


This uses the newer fscrypt and requires Ubuntu 18.10+.
<ol>
<ol>
<li>
<li>
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;Notes and Caveats
;Notes and Caveats
* <code>systemd</code> will no longer have access to your home so all startup apps should be placed elsewhere
* <code>systemd</code> will no longer have access to your home so all startup apps should be placed elsewhere
** E.g. Move all startup scripts in your <code>~/bin</code> to <code>/usr/bin</code>
** E.g. Move all startup scripts in your <code>~/.local/bin</code> to <code>/usr/local/bin</code>
* <code>ssh</code> will not work until home has been decrypted since the authorized keys are in <code>~/.ssh/authorized_keys</code>
* <code>ssh</code> will not work until home has been decrypted since the authorized keys are in <code>~/.ssh/authorized_keys</code>


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==SFTP==
==SFTP==
You can create a specific user with a chroot to limit SFTP to specific folders.   
You can create a specific user with a chroot to limit SFTP to specific folders.   
See [[Archwiki | SFTP chroot]] for details.
See [[Archwiki: SFTP chroot]] for details.
/etc/ssh/sshd_config
/etc/ssh/sshd_config
<pre>
<pre>
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   PasswordAuthentication no
   PasswordAuthentication no
</pre>
</pre>
==Hardware Info==
;Benchmarking
Basic CPU benchmark
<pre>
sysbench cpu --threads=2 run
</pre>
==MOTD==
Message of the day is the text you see when you login via SSH. 
Ubuntu stores its MOTD in <code>/etc/update-motd.d/</code>. Other distros use <code>/etc/motd/</code>. 
You can disable the Ubuntu news motd in <code>/etc/default/motd-news</code>.
==System Administration==
{{main | Linux Administration}}
==Installing Binaries==
# Copy your binary to <code>/usr/local/bin/</code> or <code>~/.local/bin/</code>
# Copy your man page to <code>/usr/local/share/man/man1/</code> or <code>~/.local/share/man/man1/</code>
==Network Troubleshooting==
On one of my OptiPlex 5060 servers, the network adapter would reset on git ssh clones.<br>
This would appear in <code>/var/log/syslog</code> as:
<pre>
Feb  8 22:22:01 optiplex5060-2 kernel: [ 4378.992607] e1000e 0000:00:1f.6 eno1: Reset adapter unexpectedly
</pre>
This was resolved by disabling TCP Segmentation Offload:
<syntaxhighlight lang="bash">
sudo ethtool -K eno1 tso off
# Verify tso is disabled
ethtool -k eno1 | grep tcp
</syntaxhighlight>
To make this persist across reboots:
{{hidden | Script |
If you're using netplan (default for Ubuntu):<br>
[https://michael.mulqueen.me.uk/2018/08/disable-offloading-netplan-ubuntu/ Reference]<br>
<syntaxhighlight lang="bash">
output_path=/usr/lib/networkd-dispatcher/routable.d/10-disable-offloading
sudo tee $output_path <<EOF> /dev/null
#!/bin/bash
ethtool -K eno1 tso off
EOF
sudo chmod +x $output_path
</syntaxhighlight>
If using ifupdown:
<syntaxhighlight lang="bash">
output_path=/etc/network/if-up.d/disable-tso
sudo tee $output_path <<EOF> /dev/null
#!/bin/bash
ethtool -K eno1 tso off
EOF
sudo chmod +x $output_path
</syntaxhighlight>
}}
==Cloning to a new disk==
The easiest way is to use gparted.
{{hidden | Terminal Guide |
To do this in the terminal:
<syntaxhighlight lang="bash">
OLD_DRIVE=/dev/sda
NEW_DRIVE=/dev/sdb
# Show old drive partitions in sectors
parted $OLD_DRIVE unit s print free
# Apply GPT
parted $NEW_DRIVE mklabel gpt
# Copy new EFI partition with start 1024s and end 1050623s
parted $NEW_DRIVE mkpart primary fat32 2048s 1050623s
# Apply boot and esp flags.
parted $NEW_DRIVE set 1 boot on
parted $NEW_DRIVE set 1 esp on
parted $NEW_DRIVE name 1 'EFI System Partition'
# dd the old to the new
dd if=${OLD_DRIVE}1 of=${NEW_DRIVE}1 bs=4k
# Make a new partition. Make sure start and end sectors are aligned.
# i.e. start % 8 == 0 and end % 8 == 7 if your physical sector size is 4096 bytes, typical for new HDDs and SSDs.
parted $NEW_DRIVE mkpart primary btrfs 1050624s 488396791s
parted $NEW_DRIVE align-check opt 2
# Copy the filesystem
mkfs.btrfs ${NEW_DRIVE}2
mkdir /media/${NEW_DRIVE}
mount -t btrfs -o compress=zstd /media/${NEW_DRIVE}2
rsync -axHAWXS --numeric-ids --info=progress2 /media/${NEW_DRIVE}2
</syntaxhighlight>
[https://superuser.com/questions/307541/copy-entire-file-system-hierarchy-from-one-drive-to-another rsync reference]
;rsync options
* -a    archive mode
* -x    one file system
* -H    preserve hard links
* -A    preserve ACLs
* -W    copy whole files instead of deltas
* -X    preserve extended attributes
* -S    handle sparse files efficiently
* --numeric-ids    use id instead of uid/gid
To copy a root partition, make sure you change the following on the new drive:
* Update the UUID and mount options in <code>/etc/fstab</code>
* Update the UUID in <code>/boot/grub/grub.cfg</code> and run <code>update-grub</code>
* Update the UUID in <code>/boot/EFI/ubuntu/grub.cfg</code>
* Run [https://help.ubuntu.com/community/Boot-Repair boot-repair] from a live disk if you run into any issues.
}}
==Ubuntu==
Ubuntu-specific notes
===Disable ESM message===
[https://askubuntu.com/questions/1453749/inhibit-esm-messages-at-login Reference]
<syntaxhighlight lang="bash">
# Disable MOTD
sudo chmod -x /etc/update-motd.d/88-esm-announce
sudo chmod -x /etc/update-motd.d/91-contract-ua-esm-status
# Disable APT check
sudo sed -Ezi.orig \
  -e 's/(def _output_esm_service_status.outstream, have_esm_service, service_type.:\n)/\1    return\n/' \
  -e 's/(def _output_esm_package_alert.*?\n.*?\n.:\n)/\1    return\n/' \
  /usr/lib/update-notifier/apt_check.py
sudo /usr/lib/update-notifier/update-motd-updates-available --force
</syntaxhighlight>
Retrieved from "https://wiki.davidl.me/view/Linux"