Tips & Tricks

Create ssh key

ssh-keygen -t ed25519 -C "comment" -f <keys-name>

Last commands exit code

echo $?

Delete only directories

rm -rf `ls -d */`
find . -maxdepth 1 -mindepth 1 -type d -exec rm -rf '{}' \;

Disable swap

cat /proc/sys/vm/swappiness
sysctl vm.swappiness=0

vim /etc/sysctl.conf
vm.swappiness=0

unrar x <filename>.rar

Upgrade all outdates pip packages

pip list --outdated
pip install -U `pip list --outdated | awk 'NR>2 {print $1}'`

Clean /boot & /usr disk, freeing inodes

First try

apt autoremove
apt autoremove --purge
purge-old-kernels

If unsuccessful, then

# Check your kernel
uname -r
cat /proc/version

# List installed kernels, headers, modules
dpkg --list 'linux-*' | grep ^ii
apt list --installed linux-*

# Remove and purge unnecessary ones
apt remove --purge linux-{headers,image,modules,modules-extra}-4.15.0-1*
apt remove --purge linux-{headers,image,modules,modules-extra}-4.15.0-20[0-6]

certain numbers/names - {1,2,3}
certain range - [1-3]

# Check iu packages
dpkg --list 'linux-*' | grep "^iU"

# Remove if necessary
apt remove --purge $(dpkg -l | grep "^iU" | awk '{print $2}')

JMXterm example

https://www.googlecloudcommunity.com/gc/Cloud-Product-Articles/How-to-Read-JMX-Statistics-via-The-Shell/ta-p/77629

java -jar jmxterm-1.0.2-uber.jar
jvms
open <PID>
beans
get -b java.lang:type=Memory *
get used -b java.lang:type=Memory HeapMemoryUsage

Kick ssh session

who -u
echo "HAHA" | write user1 pts/2
kill -9 24995

putty pub2 to linux format

ssh-keygen -i -f <pub2>

restart network interface

ip link set ens160 down && ip link set ens160 up

journalctl vacuum

journalctl --disk-usage
journalctl --rotate
journalctl -D /var/log/journal/ --vacuum-size=100M
journalctl --verify

Measure command or script execution time

time <command or script>

Create user wo password

adduser <user> --disabled-password --force-badname

Add user to group

usermod -a -G <group> <user>

Remove user from group

gpasswd -d <user> <group>

Change shell to Bash

sudo usermod -s /bin/bash $USER

Switch iTerm2 to Bash

chsh -s /bin/zsh

Get pid info

cat /proc/pid/cmdline

Get key from port 80

apt-key adv --keyserver hkp://keys.gnupg.net:80 --recv "E775D097"

Sudo without password

create group, for ex named wheel
sudo visudo and add the line below to it
wheel ALL=(ALL) NOPASSWD:ALL
run usermod -a -G wheel $USER

Fix locale

open /etc/environment

LANGUAGE="en_US.UTF-8"
LANG="en_US.UTF-8"
LC_ALL="en_US.UTF-8"

locale-gen en_US.UTF-8

See lib-s waiting to be "updated"

lsof | grep lib | grep DEL

Attach NAS

Mac

Finder -> Go -> Connect to Server afp://LS520DE2a5.local/<dir>

Linux

mkdir /mnt/nas-plex

add to /etc/fstab

//{{ nas_host }}/Plex /mnt/nas-plex username={{ nas_username }},password={{ nas_password }},iocharset=utf8,uid=1000,gid=1000

mount -a

Win

Computer -> add a network location ->  \\hostname\dir

My external IP

curl ifconfig.me

View CSR

openssl req -text -noout -verify -in CSR.csr

View certificate

openssl x509 -in certificate.crt -text -noout

Copy ssh key to machine

ssh-copy-id <hostname or IP>

Measure command execution time

time <command>

List All Directories

ls -d */

Move Directory One Lv Down

mv Math/ ../

Directory Size

du -hs <dir_name>

Check Storage

df -h

Show Linux distro info

lsb_release -a

Show certificate info

openssl x509 -in certificate.crt -text -noout

Delete all mail

mail
d *
q

Show cpu stats / list cores

lscpu
cat /proc/cpuinfo
cat /proc/cpuinfo | grep processor | wc -l

Select default editor for logged in user

select-editor

Count process open file handlers

ls /proc/my_pid/fd | wc -l

Traceroute

Linux mtr qrl.ee
Windows tracert qrl.ee

Count open files (The value does not apply to a root user, so if you want to tally with the lsof output, exclude files opened by root)

lsof|wc -l

Open files limit by OS

cat /proc/sys/fs/file-max

Create trash 10MB base64 filled file

base64 /dev/urandom | head -c 10000000 > file.txt

Create trash 1MB text filled file

yes "HelloWorld" | head --byte=1100000 > 1MB.txt

Virtualbox shared folder

Go to Devices option of your VM and click on the Shared Folders option and add the required_folder you want to share.
Now in your file system (root) you can see media/sf_required_folder.
But by default the Guest User won't have access to this folder.
So to grant access to this folder you need to add Guest user to the group vboxsf.
For this, sudo adduser Guest_user vboxsf to give access.
Now have the access.