Linux

Set Rstudio theme

See Rstudio theme file.

Increase swap space

https://askubuntu.com/questions/178712/how-to-increase-swap-space

Encrypt/Decrypt files

gpg -c filename
gpg -d filename.gpg

Don’t ever cache the password:

vim ~/.gnupg/gpg-agent.conf

# copy-paste following two lines
default-cache-ttl 1
max-cache-ttl 1

echo RELOADAGENT | gpg-connect-agent

CPU and MEM usage (top)

Single commands:

# CPU: how many CPU/cores
top -b -n1 -u $(whoami) | awk 'NR>7 {sum+=$9} END {print sum/100, "cores"}'
# MEM: how many GB? (RES)
ps -u $(whoami) --no-headers -o rss | awk '{sum+=$1} END {print sum/(1024*1024) " GB"}'

Using watch:

#!/bin/bash

watch -n 1 '
# CPU usage
cpu=$(top -b -n1 -u $(whoami) | awk '"'"'NR>7 {sum+=$9} END {print sum/100, "cores"}'"'"')

# MEM (RES) usage
mem=$(ps -u $(whoami) --no-headers -o rss | awk '"'"'{sum+=$1} END {print sum/(1024*1024) " GB"}'"'"')

# Output the results
echo -e "CPU Usage: $cpu\nMemory Usage: $mem"
'

Break paragraph to multiple sentences, each in a new line

Paragraph is like: AAaa. Bbbbb. Cccc.. What you get is: AAaa.\nBbbbb.\nCccc.

sed -i 's/\. /\.\n/g' test.txt

Find start time of a long-running process

ps -eo pid,lstart,cmd | grep process_name

Find pattern in files and retrieve file name as well

Find in all .html files inside a directory, the mentions of string xaxa:

find . -name \*.html -print0 | xargs -0 grep -n -H xaxa

Find pattern recursively in directories and files

E.g. my current directory has multiple directories that each one has multiple files which I want to cat and find a pattern:

find . -type f -exec cat {} + | grep stable | wc -l

Rename files

Let’s say I have many files in a directory which have the sub-string _rand_ and I want to change that sub-string to _whatever_. Run inside the directory:

for file in `ls | grep "_rand_"`; do mv "$file" "${file/_rand_/_whatever_}"; done

Mount external disk

sudo fdisk -l
# usually it's on `/dev/sdb1` partition
mkdir /media/disk
sudo mount /dev/sdb1 /media/disk

After you are done, run:

sudo umount /media/disk

Add command path permanently

cd /etc/profile.d
vim test.sh

# add lines
EXEC_HOME=/usr/bin/my-exetutable
export EXEC_HOME

# test
echo $EXEC_HOME

Counter with dots

To see an incremental counter:

i=0; while true; do sleep 1; echo $i; i=$((i+1)); done

To see dots (server connection awaiting!):

while true; do echo -n .; sleep 1; done

Ubuntu text scaling

Make all text bigger/smaller:

# big
/usr/bin/gsettings set org.gnome.desktop.interface text-scaling-factor 1.5
# small
/usr/bin/gsettings set org.gnome.desktop.interface text-scaling-factor 1.1

Nice bash aliases

# choose file to put the aliases
vim ~/.bashrc 
vim ~/.bash_aliases # better

alias 'com'='git commit'
alias 'cam'='git commit --amend'
alias 'gt'='git status'
alias 'updocs'='git add docs; git commit -m "update docs"'
alias 'disk'='df -h | grep -v loop'
alias 'l'='ls -ltrh'
alias 'off'='sudo poweroff'
alias 'useful'='cd ~/repos/useful'
alias 'p8'='ping 8.8.8.8'
alias 'renet'='sudo service network-manager restart; i=0; while [[ $i < 6 ]]; do echo -n .; sleep 1; let i=i+1; done; echo "";'
alias 'ssh-server'='ssh name@server'
alias 'ssh-server'='ssh -J name@proxy-server name@main-server'

Change terminal prompt look

Add to ~/.bashrc this line:

export PS1='\[\033[01;32m\]\u\[\033[00m\]:\[\033[01;34m\]~\[\033[00m\]\$ '

or this one that includes the name of the current working dir:

export PS1='\[\033[01;32m\]\u\[\033[00m\]:\[\033[01;36m\][\W]\[\033[00m\]\$ '

Notes:

  • 32m => green, 00m => white, 34m => blue, 36m => Cyan
  • \u => user, \W => working dir

Extract specific characters from each line in a file

cut -c 1-30 filename

Do something on many files in a dir

Something can be: rendering notebooks to HTML or checking if the files are the same as other files for example

#!/bin/bash

files=`ls`
dir="/somewhere/over/the/rainbow"
rmd_files=`ls | grep Rmd`

for file in ${rmd_files}; do
  filename_no_extension="$(basename "${file}" .Rmd)"
  diff -s $dir$file $file
  Rscript -e "library(rmarkdown); rmarkdown::render(\"./$file\",\"html_document\")"
done

Make desktop icons appear and disappear

/usr/bingsettings set org.gnome.desktop.background show-desktop-icons false

Find total MB of files in a dir

ls | xargs stat --format=%s | awk '{s+=$1} END {print s/(1024*1024)}'

Count lines of source code

find . -name '*.php' | xargs wc -l
# or use cloc: 
apt-get install cloc

Delete files fast

find . -maxdepth 1 -name "something*" -print0 | xargs -0 rm

List files in a dir efficiently

Copy the listdir.c file. Then:

gcc listdir.c -o listdir
./listdir /dirWithTooManyFiles

Count and change the reserved space in an ext4 partition ‘ONLINE’

Change the reserved space to 1%:

tune2fs -m 1 /dev/sdb1

Count the percentage:

a=$(tune2fs -l /dev/sdb1 | grep -i 'Reserved block count' | awk '{ print $4 }')
b=$(tune2fs -l /dev/sdb1 | grep 'Block count' | awk  '{ print $3 }')
echo "scale=5; ($a/$b)*100" | bc # this is the percentage of the reserved space

Kill many processes at once (that match a pattern)

ps aux | grep -v grep | grep -i patternToMatch | awk '{print $2}' | xargs kill -9

Deleting file descriptors

After deleting many files, the space is not freed and you need to delete the file descriptors:

find /proc/*/fd -ls 2> /dev/null | awk '/deleted/ {print $11}' | xargs -p -n 1 truncate -s 0

Find number of CPUs and model

grep -c processor /proc/cpuinfo
lscpu
nproc
cat /proc/cpuinfo | grep name | tail -n1

Dynamic linking

ldd <executable_name>

if you see not found for some library, put the <something>.so.x.x.x file in: /usr/local/lib

ln -s <something>.so.x.x.x <something>.so.x` # or whatever is needed
ldconfig -v

ldd <executable_name> # should be OK now

Change hostname

# Stop MySQL if it is running
service mysql stop
old hostname = old-name
new hostname = new-name

In the next 2 files change old-name to new-name:

vim /etc/hosts
vim /etc/hostname

and execute:

hostname new-name
# check
hostname

Restart MySQL (if needed):

service mysql start

Service tag

dmidecode -t system

See cached files info in the pwd

linux-fincore --pages=false --summarize --only-cached *

Clean cached memory

sudo sysctl vm.drop_caches=3
sync && echo 3 | tee /proc/sys/vm/drop_caches

Build an ext4 filesystem on a disk partition

cat /etc/fstab
fdisk -l
cfdisk /dev/sdc
mkfs.ext4 /dev/sdc1
mount -a
df -h