How to ... in Linux (in examples)

lsb_release -a
more /etc/*-release
uname -r

ifconfig -a

ip addr show

more /proc/cpuinfo

which command
whereis command     #(gives further information)

more /proc/meminfo

find . -name file-name -print

lspci | grep -i usb

gconf-editor

sudo reboot

sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade     #(to upgrade distribution)

sudo apt-get remove package-name

Download required iso file
Load start-up disc creator

$PS1     #(for single line prompt variable)
$PS2     #(for multiple lines)
#E.g. in .bashrc:
PS1=$USER"> "

$#     #(number of arguments)
$1     #(first argument, e.g.)
$*     #(all arguments)

item=$(echo $LIST | awk ’{print $’$N’}’)
or
item=${LIST[N]}  # N=0 is first item

ItemsinList=${#List[@]}

LIST=$(ls)
# or
LIST=‘ls‘

file=’file-description.txt.abc’
part1="${file#*-}"     # strip part before -
part2="${part1%%.*}"   # strip after the first .
part3="${file##*.}"    # get part after the last .

STRING="text string"
${#STRING}        # Returns the string length
${STRING:pos}     # Returns the substring after pos (0 is start of string)
${STRING:pos:len} # Returns the substring after pos for len characters

printf "format-descriptor" variable-to-output
# e.g.
printf "%02u" 4     # Will output 04

let N1=$A+$B
let N2=$A-$B

TEMP=‘wc -l filename‘
N_FILES=$(echo $TEMP | awk ’{print $’1’}’) 

cat > output-file-name << EOF
# Stuff-to-put-in-file
EOF

for VARIABLE in item1 item2 ...
do
  echo $VARIABLE
done
​
for NUM in {1..10}
do
  echo $NUM
done
​
for NUM in $(seq $START $FINISH); do
  echo $NUM
done

if [-e file-name]; then
  echo "File exists"
else
  echo "File does not exist"
fi
​
# (else branch optional)
# -e = file exist test
# -f = file is not a directory or device
# -s = file non-zero
# -d = file is a directory
# -b = file is a block device
# -c = file is a character device
# -p = file is a pipe
# -h = file is a symbolic link
# -L = file is a symbolic link
# -S = file is a socket
# -t = file is associated with terminal
# -r = file has read permissions
# -w = file has write permissions
# -x = file has execute permissions

if [ $a == $b ]; then
  echo “a equals b”
fi

# Go through filename line-by-line
COUNT=0
while read -r LINE; do
  let COUNT=$COUNT+1
  echo $COUNT $LINE
done < filename

sudo --login -u username
su username     #(preferred)

ctrl-alt-F2     #(login to shell)
ctrl-alt-F7     #(graphics mode)
ctrl-alt-T      #(terminal)

gpg -o encrypted-file -c original-file            #(encryption)
gpg -o decrypted-file --decrypt encrypted-file    #(decription)

chown user file-or-directory     #(changes owner)
chown :user file-or-directory    #(changes group)
chown user: file-or-directory    #(changes owner and group)

chmod abc file-or-directory  #(a for user, b for group, c for world)
# a,b,or c = 4*read + 2*write + execute
# (read, write, execute = 0 or 1)
​
# Examples
# Read only = 4
# Write only = 2
# Read and write = 6
# Read, write, and execute = 7
# Read and execute = 5

# Generate a pair of keys
# Run from home directory on local host (press ENTER at all prompts, except ’y’):
ssh-keygen
​
# Append the file generated (.ssh/id_rsa.pub) to .ssh/authorized_keys on the remote host
# Run on local host:
ssh_copy_id -i ~/.ssh/id_rsa.pub remote-host-name
​
# If the above does not work, then do the following
# Run on local host:
rsync ~/.ssh/id_rsa.pub remote-host-name:.ssh/
# Log into remote host
# Run on remote host:
cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

pdftk file.pdf output password_protected_file.pdf owner_pw password user_pw a_different_password

split --bytes=1M big-file small-files-prefix

cat small-files-prefix* > new-big-file

cut -cx- file
# (will need to redirect output to another file)

grep search-term file-name
# options
# -i ignore case
​
grep -P "\t" file-name     searches for special characters (here \t=tab)
grep "^vTAB"     alternative method to above (^v=ctrl-v, TAB=tab key)

paste -d ’,;’ file-name1 file-name2 file-name3...     (,; ... are delimiting characters, redirect to output file)

sed -i ’s/string1/string2/g’ file-name
# (tab character is [\t])
# (The s command with sed allows you to use any delimitor (/ in the above)
#  whatever follows s is used)

lpr file-name.pdf     (default printer, default settings)
lpr file-name.pdf -P printer-name -o number-up=2     (prints to specified printer with two pages per side)
# Other options:
# -#copies
# -o sides=two-sided-short-edge
# -o sides=two-sided-long-edge     (default)
# -o page-ranges=1,4-8
​
lp file-name.pdf -d printer-name -o number-up=2     (prints to specified printer with two pages per side)
# Other options:
# -n copies
# -o sides=two-sided-short-edge
# -o sides=two-sided-long-edge     (default)
# -o page-ranges=1,4-8

pdfposter -p2x2a4 Poster.pdf ManyA4Pages.pdf

cat file-name.pdf | ssh user@host "lp -d printer-name -U user-name other-options (as above)"

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=output-file.pdf input-file1.pdf input-file2.pdf ...

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dQUIET -dFirstPage=first-page -dLastPage=last-page -sOutputFile=output-file.pdf input-file.pdf

gfortran
​
# To use netcdf routines include the following in source code:
INCLUDE ’/usr/include/netcdf.inc’
​
# To compile code using netcdf, include the following linker options:
-I/usr/include/ -L/usr/lib -lnetcdff -lnetcdf

gcc

g++
​
# To use netcdf routines include the following in source code:
#include <netcdf.h>
​
# To compile code using netcdf:
g++ -I/usr/include file-name.cpp -L/usr/lib -lnetcdf_c++ -lnetcdf

nmcli nm enable true

# A machine has max resolution of 1024x768, but my monitor has 1280x1024
​
# What resolutions are currently available on the computer?
xrandr
​
# Find out what resolution you require (e.g. monitor documentation)
# e.g. 1280x1024 Hor 63.98 kHz Vert 75
​
# If this required resolution is not available, then add the following commands to the .profile file
cvt 1280 1024 75
xrandr --newmode "1280x1024_75.00" 109.00 1280 1368 1496 1712 1024 1027 1034 1063 -hsync +vsync
# (N.B. the stuff following --newmode is copied from the output of the cvt command)
xrandr --addmode VGA1 1280x1024_75.00
​
# The new resolution will then appear in the list of monitor resolutions available.

alsamixer
pulse audio

# Example to map Sun keyboard AltGr key to act as right Ctrl key
# Place the following in .profile
setxkbmap -option ctrl:ralt_rctrl

watch -n delay-in-seconds linux-command
​
# or
​
while true; do
sleep delay-in-seconds
# linux-command
done

linux-command | tee output-file

jobs

# ctrl-z
bg

linux-command &
# (process-id is displayed)
disown process-id
logout
# (ignore comment about running jobs)
​
# or
​
nohup linux-command < Input-stuff > output-stuff

kill -STOP process-id

kill -CONT process-id

ssh user@host "remote command"

sudo ufw enable
# To check:
sudo ufw status verbose

sudo add-apt-repository ppa:lyx-devel/release
sudo apt-get update
sudo apt-get install lyx

f95 UserCode.f90 -L/usr/local/lib -lexample compiler-options