Linux

awk '{print $1 " " $2 " " $3 " " $4}' file.csv # prints the first 4 columns of file.csv
awk '{print $1 " " $2 " " $3 " " $4}' file.csv | head -n 5  # prints the first 5 rows and 4 columns of file.csv

chmod 755 <executable filename>    # Change the permission so you can execute it.
chmod u+x <executable filename>    # Another method to add execute permission to the file.

export <variable name>=<variable value>   # Syntax. For example, see below!
export PATH=$PATH:<path to add>          # To add a path to the PATH variable
export -p                                # To list all the environment variables. You can use other variable names like `HOME`, `EDITOR`, etc.
env                                      # Alternative way to list all the environment variables. For more, read https://en.wikipedia.org/wiki/Env
export EDITOR=<editor name>              # To set the default editor

head -n 5 <file.txt>  # prints the first 5 lines of <file.txt>

kill <PID>   # To kill a process with a specific PID
kill $(pidof <process name>)   # To kill a process with a specific name. For e.g. `kill $(pidof firefox)`
kill -SIGSTOP <PID>   # To pause a process with a specific PID. You can also do `kill -SIGSTOP $(pidof <process name>)` which will pause all the processes with the same name.
kill -SIGCONT <PID>   # To resume a process with a specific PID. You can also do `kill -SIGCONT $(pidof <process name>)` which will resume all the processes with the same name.

$ ln -s /mnt/<YourPartition> ~/<folder to which you want to symlink>   # To create a symlink folder of mount partition

ls -al   # To list all the files in a directory with their permissions, size, date and time of last modification
ls <file>-*  # To list all the files in a directory with a specific pattern
ls -1 | wc -l   # To count the number of files in a directory
                # (how?: `ls -1` to list all files in a directory and
                # `wc -l` to count the number of files.
                # Note: | to pipe the output of ls to wc)
ls <file>-* | wc -l   # To count the number of files in a directory with a specific pattern
ls -lh   # gives human readable file sizes, long format.

more <file.txt>

nohup <command> > log.out &                      # Replace <command> by command name and dump the terminal output to log file named log.out. You can change the name and path of log file.
nohup <command> > log.out & echo $! > save.pid   # Save the PID of the nohup command to save_pid.txt OR another way is using jobs command

# If you are using tmux and you are in the same terminal session where you ran nohup then, you can use jobs command
jobs -l                                          # To list all the jobs with their PIDs

ocrmypdf <input PDF file> <output PDF file>  # To convert a PDF file to a PDF file with OCR text layer.
ocrmypdf --force-ocr <input PDF file> <output PDF file>  # To convert a PDF file which has already with text layer to a PDF file with OCR text layer
ocrmypdf --skip-text --oversample <DPI> <input PDF file> <output PDF file>  # To compress the PDF file. See https://ocrmypdf.readthedocs.io/en/latest/cookbook.html?highlight=--oversample%20#improving-ocr-quality
                                                        # Use DPI to be 150, as reference to ghostscript flag -dPDFSETTINGS=/ebook. See https://ghostscript.com/docs/9.54.0/VectorDevices.htm#distillerparams or you can use`ps2pdf -dPDFSETTINGS=/ebook <input PDF file> <output PDF file>`

ps faxu     # To display all the processes in a tree format of all users in the system
ps faux --sort -rss | head -10     # Sort processes by memory used and see the top 10 processes
ps faux --sort -%cpu | head -10    # Sort processes by CPU and see the top 10 processes
px fxu      # To display all the processes in a tree format of your only.

pushd <directory>
popd

scp <filename> <remote username>@<remote ip>:<remote path to copy>  # Copy a local file to a remote system
scp <filename> <remote username>@<remote ip>:./<folder name>  # Copy a local file to remote system of a 1-level folder from home directory
scp <remote username>@<remote ip>:<path of remote file> <local path to copy>  # Copy a remote file to a local system
scp <remote 1 username>@<remote 1 ip>:<path of remote file> <remote 2 username>@<remote 2 ip>:<remote 2 path to copy>  # Copy a file from remote 1 to remote 2

ssh <username>@<hostname>   # To connect to a remote Linux system
ssh <username>@<hostname> -p <port>   # To connect to a remote Linux system with a specific port
ssh <username>@<hostname> -t <command>   # To execute a command on a remote Linux system.
ssh -tt <username1>@<hostname1> "ssh <username2>@<hostname2>"  # To connect directly to hostname2 with username2.

# If you see ths below error:
#@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
#@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
#@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# Then, remove the line where you see the hostname from the `known_hosts` file.
nano ~/.ssh/known_hosts
# Now, in the next time you will connect to that host, you will be asked to generate a new key and you approve it.

sshfs <remote username>@<remote ip>:<remote path> <local path>   # Mount remote path to local path
fusermount -u <local path>   # Unmount local path

# jumphost or proxy jump
sshfs <remote 2 username>@<remote 2 ip>:<remote path> ~/<local folder path to mount> -o ssh_command='ssh -o PreferredAuthentications=password -J <remote 1 username>@<remote 1 ip>'  # Mount remote path to local path with proxy jump. Here we have: remote 1 is the jumphost and remote 2 is the remote server that we want to mount. (i.e. localhost -> remote 1 -> remote 2)

# You can do the same thing by including below settings in your ~/.ssh/config file:
###--- Start here ---###
Host jumphost
    Hostname <remote 1 ip>
    User <remote 1 username>
    Port <port number, default is 22, optional, you can skip>
    ForwardAgent yes

Host drive
    Hostname <remote 2 ip>
    User <remote 2 username>
    Port <port number, default is 22, optional, you can skip>
    ForwardAgent yes
    ProxyJump jumphost
###--- End here ---###
# Note that ForwardsAgent is optional, if you don't want to forward agent, you can remove it. 'jumphost' and 'drive' is just a random name I gave.

tail -100 file.txt      # Read last 100 lines, strongly suggest to use tmux so that you can go scroll up
tail -100 file.txt > dumpfile.txt     # Copy last 100 lines to dumpfile.txt
tail -f file.txt      # Not to stop tail command even when it reaches the EOF (end of file). Useful while reading the appending file

top -H -p <pid>   # To view all the threads by program process id.

watch -n 1 -d <file.txt>      # Monitor <file.txt> every 1 second and display the changes

wc -l <file>    # To count the number of lines in a file

du -sh <folder name>  # To check the size of a folder
touch <file.txt>      # Create a file.txt
uptime                # returns information about how long your system has been running together

mkdir $HOME/.dotfiles
git init --bare $HOME/.dotfiles
echo "alias config='/usr/bin/git --git-dir=$HOME/.dotfiles --work-tree=$HOME'" >> $HOME/.YourShell-rc-File

echo "alias config='/usr/bin/git --git-dir=$HOME/.dotfiles --work-tree=$HOME'" >> $HOME/.zshrc

alias config='/usr/bin/git --git-dir=$HOME/.dotfiles --work-tree=$HOME'"

config add .filename
config commit -m "+ .filename"

config push origin master

sudo su

/home/username#

gedit /etc/sysctl.conf

vm.dirty_background_ratio = 5
vm.dirty_ratio = 10

sysctl -p

rm /var/tmp/lm_TMW*

rm -rf /usr/local/MATLAB/R2010b

rm /usr/local/bin/matlab /usr/local/bin/mcc /usr/local/bin/mex /usr/local/bin/mbuild

sudo dd if=/dev/zero of=/dev/sda bs=1M count=8 && sync

exec --no-startup-id udiskie -nas

sudo mkdir /media

sudo nano /etc/udev/rules.d/99-udisks2.rules

ln -s /media ~/External\ Devices