Linux System Admin

Linux_System_Admin.md

User related

sudo -u nobody bash Change the user to a desired name with a desired shell.

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