Linux Notes
Common Commands
How to show file permission?
ls /var/www -al
How to add a user?
sudo adduser new_username
// or
sudo useradd new_username
How to remove a user?
sudo userdel username
// remove user's home folder
sudo rm -r /home/username
How to change other user’s password?
// set / change password for user postgres
sudo passwd postgres
How to add a user to sudo group?
adduser username sudo
// or
usermod -aG sudo username
How to execute commands as other user?
su // as root
su - postgres // login as postgres
su postgres // switch to postgres
// preserve the entire environment (HOME, SHELL, USER, and LOGNAME) of the calling user
su -p postgres
How to change file permission?
See https://help.ubuntu.com/community/FilePermissions
- By changing file ownership?
cp ~/.ssh/authorized_keys ~[username]/.ssh/authorized_keys
chown -R [username]:[username] ~[username]/.ssh
- By changing file permission
sudo chmod -R 777 /var/www/html/
How to list all users?
cat /etc/passwd
// or
cut -d: -f1 /etc/passwd
Ubuntu
How to reboot system?
sudo reboot
sudo shutdown -r // after two minutes: shutdown -r +2
// 0 - Power off the machine
// 1 – Enter rescue mode
// 2,3,4,5 – Start runlevelX.target unit
// 6 - reboot
init 6
How to show ubuntu version?
Press Ctrl + Alt + T open terminal and type the following command:
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 19.04
Release: 19.04
Codename: disco
How to use systemctl?
systemctl daemon-reload
systemctl status caddy
// systemctl start starts (activates) the service immediately
systemctl start caddy
systemctl restart caddy
// systemctl enable configures the system to start the service at next reboot
systemctl enable caddy
How to upgrade from Ubuntu Linux 16.04 to 18.04
$ sudo apt update
$ sudo apt upgrade
$ sudo reboot
// optional 1: open port 1022
// $ sudo ufw allow 1022/tcp comment 'Temp open port ssh tcp port 1022 for upgrade'
// optional 2: or temporate disable filewall
// $ sudo ufw status
// $ sudo ufw disable
// $ sudo ufw enable
$ sudo do-release-upgrade
// verify
$ uname -r
// optional: remove port 1022
// $ sudo ufw delete allow 1022/tcp
Why repository no longer has a Release file?
When I run sudo apt-get update command, it shows:
E: The repository 'http://security.ubuntu.com/ubuntu disco-security Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
Reason:
Ubuntu 19.04 is pass end-of-life and the release files are removed from the repository
Solution:
Change all of your apt-sources to “old-releases.ubuntu.com”.
This sed command works with any/all ubuntu.com URLs and saves a backup copy in case you need to revert:
sudo sed -i.save -e 's/\/\/.*ubuntu.com/\/\/old-releases.ubuntu.com/g' /etc/apt/sources.list
Upgrade all packages in your current (old and outdated) release and make sure you have the update manager installed:
sudo apt-get update
sudo apt update && sudo apt full-upgrade -y
//sudo apt-get dist-upgrade
//sudo apt-get install update-manager-core
sudo reboot
// Upgrade to the latest release:
sudo do-release-upgrade
How to run donation program?
chmod +x ./donation
andrew@svr:~/go/src/shareverses$ sudo -b ./shareverses >> log.txt
andrew@svr:~/main$ sudo caddy start
sudo -b ./donation > log.txt
// to stop it if it is running
ps -eaf | grep donation
// kill it by the process id xxx
sudo kill xxx