Linux
Table of contents
User related
sudo -u nobody bash Change the user to a desired name with a desired shell.
Add or Remove User
Add user with a home directory: sudo adduser --home /home/rohit rohit
Delete user: sudo deluser rohit
Add a User to Sudoer List
usermod -a -G sudo rohit
Cron Jobs Log
grep CRON /var/log/syslog
Monitoring Processes (ps command)
More information at (https://www.tecmint.com/ps-command-examples-for-linux-process-monitoring/)
ps -eo user,pid,ppid,cmd,%mem,%cpu --sort=-%mem | head # Top running processes by highest memory usage.
ps -eo user,pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head # Top running processes by highest cpu usage.
kill -9 2583 2584 # Kill a process using its PID.
System Update
Apt
To update and install packages.
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install
sudo apt-get install vsftpd=2.3.5-3ubuntu1 # Install specific version of the package.
sudo apt-get remove vsftpd # Remove package without removing configuration.
sudo apt-get purge vsftpd # Completely remove package along with its configuration.
sudo apt-get remove --purge vsftpd # Can combine both remove and purge.
sudo apt-get clean # Delete downloaded .deb files.
sudo apt-get autoclean # Delete all .deb files.
sudo apt-get check # Check for broken dependencies.
Apt Cache
To query apt package list.
apt-cache pkgnames # List all available packages.
apt-cache search vsftpd # Search for a particular package.
apt-cache pkgnames vsftpd # List all the packages starting with a particular name.
apt-cache show netcat # Check package information.
apt-cache showpkg vsftpd # Check dependencies of a particular package.
Install Using DPKG
sudo dpkg -i package_with_unsatisfied_dependencies.deb
sudo apt-get -f install
Unattended Auto Upgrade
sudo apt-get install unattended-upgrades
sudo dpkg-reconfigure unattended-upgrades
https://help.ubuntu.com/lts/serverguide/automatic-updates.html
File Transfer
Rsync
Transfer Updated Files Over SSH
rsync -h -v -r -P -t remoteuser@remotehost:/foo/bar /foo/bar