Linux cheatsheet (Ubuntu)

Linux-cheatsheet.sh

# 0. need root access to system

#### Show environment variables
printenv

#### Set env var
export FOO=BAR

#### Set env var for root 
# sudo export FOO=BAR doesnt work! (see https://askubuntu.com/questions/272637/i-have-a-problem-when-using-export-command)
# change to root first
sudo -s
export FOO=BAR

#### check Linux distro
cat /etc/os-release

#### check Ubuntu version
lsb_release -a

#### Add User with sudo priviledges

# Add user 
adduser tom
# Add Password to new user 
passwd tom

# Add sudo priviledge to tom

# 1st make sure, in file /etc/sudoers there´s the following lines:
# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

# create sudo group with 
groupadd sudo

# Add user tom to sudo group
usermod -aG sudo tom
sudo adduser <username> sudo

#prevent sudo from promting for password, add following file /etc/sudoers.d/sudoers with line:
%sudo ALL=NOPASSWD: ALL


#### Install apt-get
wget http://security.ubuntu.com/ubuntu/pool/main/a/apt/apt_1.0.1ubuntu2.17_amd64.deb -O apt.deb

# Resource-Mgt

### get processors count
grep -i "physical id" /proc/cpuinfo | sort -u | wc -l 

### get RAM size
free
# or
cat proc/meminfo

### get directory size
du -sh /my/directory
# show free space
df -h /my/directory

### Debug / Identify Upstart Errors
cat /var/log/syslog


## Alpine

#### install curl
 apk --no-cache add curl

# show process that uses specific port
netstat -vanp tcp | grep 8080

 
# DNS lookup
dig jonashackt.io

# show last added txt records
dig _acme-challenge.gitlab.jonashackt.io txt


# Recursively copy directory incl. contents from remote machine to local & preserve permissions, times, modes etc.
scp -rp user@your.machine.lan:/opt/foo/bar/path/yourDirectory /home/jonashackt/Downloads/

# Pack archives
tar czf name_of_archive_file.tar.gz name_of_directory_to_tar
# Unpack
tar -xzvf name_of_archive_file.tar.gz

tar -xvf name_of_archive_file.tar

### Pass Variables to Bash Script
https://www.baeldung.com/linux/use-command-line-arguments-in-bash-script