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linux operations (without containers)

misc

  • find file anywhere: sudo locate filename (index is updated once a day. recreate with sudo updatedb)
  • find a file which contains a string : grep -nr 'search*' /opt/app/
  • find where a on the path is saved: which execuableName

check hardware

  • lshw - cpu cores and frequency and ram
  • lsblk - check disk size

permissions

image-linux-file-permission

Source of image

  • Unix permission bit calculator
  • not binary format
  • Roles:
    • u = user
    • g = group
    • o = other
  • Permission:
    • r = read
    • w = write
    • x = execute
  • You can also use binary format
  • three numbers (e.g. 755)
    • first: user
    • second: group
    • third: other
  • value of permissions
    • read: 4
    • write: 2
    • execute: 1
  • default permission bits are defined by the umask

You can set the owner user and the owner group of a file with chown.

# set user and group as ownder of the direcoty and all its content
sudo chown -R user:group /var/myfolder

To handle the rights of a file you can use chmod. 

# add execute rights for the (owner) user
sudo chmod u+x /opt/myapp/config/start.sh
# remove execute rights for others 
sudo chmod o-x /opt/myapp/config/start.sh

# remove write and read rights from the group of a file 
sudo chmod g-rw /opt/myapp/config/config.properties
# remove  write and read rights from the group of a file for every file in the directory 
sudo chmod -R g-rw /opt/myapp/config/

root

  • sudo
  • su
  • su - changes environment (e.g ~/bashrc, )

install application

Assumes that you need to use tar balls. If you use a package manager most or all of the steps will be done automatically depending on the package manager you used.

  1. add a user and a group
  2. download tar and extract it to /opt/
  3. configure application to save data and log outside of the installation folder
  4. define a service for the application

user management

Add user

# list users
cat /etc/passwd

# create user
sudo useradd username

Add user to group (e.g. to sudo group):

# list groups 
cat /etc/group

# list groups for user
id username

# create group
sudo groupadd groupname

# add user to group
sudo usermod -aG groupname username
# For the changes to take effect you need to logout the user.OR it may suffice to run one of the following commands:
# newgrp - groupname
# sudo su - $USER
# when using vscode remote kill the remote vs code server

# add to sudo group (sudoers) 
sudo usermod -aG sudo newuser
# you may want to take a look into the file /etc/sudoers if the group sudo does not exist

Add public ssh key to user

e.g. for connecting remotely to this user with the corresponding private key

# create a ~/.ssh/ folder if it does not exist
mkdir -p ~/.ssh/
printf "<content of pub key>" >>  ~/.ssh/authorized_keys
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

# ALTERNATIVE: Execute from remote to add your own key to the server (works only if you have a password or other authentification mechanism yet)
ssh-copy-id -i ~/.ssh/mykey user@host

Add private ssh key to user

e.g. for authentication on another machine where the public/private key pair is authorized

ssh-keygen -t rsa -b 4096

Allow user to use sudo

# either in /etc/sudoers.d/local

# or just add to a special group which might be sudo
sudo adduser $USER sudo
# or another special group like operator or such

# to disable password prompt when using sudo: 
## opens /etc/sudoers but with syntax check
sudo visudo

tar - unzip files

You have the following tar file: softwarename-1.2.3.tar.gz

  • Unzip with wildcard (e.g. to omit version): tar xzvf softwarename-*.tar.gz -> folder: softwarename-1.2.3
  • Unzip to a target folder: tar xzvf softwarename-1.2.3.tar.gz -C /opt -> folder: /opt/softwarename-1.2.3
  • Unzip to a target folder and set a new folder name: tar xzvf softwarename-1.2.3.tar.gz && mv softwarename-1.2.3/* /opt/softwarename -> folder: /opt/softwarename

systemd - run an application as a service

A service is a way to start a application as a daemon process. How to create a service depends on which linux you use. The old system is called system V ("system five") (initd). The following assumes that you use the newer systemd.

why?

how

create a service in systemd you need to create a so called unit file:

  • in direcotry /etc/systemd/system/
  • File with ending '.service'
  • containes '[Unit]' and '[Service]' and '[Install]' block

Interact with a service:

  • Status of service: systemctl start
  • Start service: systemctl start
  • Stop service: systemctl stop
  • Restart service: systemctl restart
  • At system startup: systemctl enable
  • At system startup: systemctl disable

memomory consumption

# memory usage in kb
ps aux --sort -rss | head