uname

uname -m Display the type of the current hardware platform.

uname -n Display the name of the system.

uname -r Display the current release level of the operating system.

uname -s Display the name of the operating system implementation.

uname -vDisplay the version level of this release of the operating system.

uname -a Behave as though the options -m, -n, -r, -s, and -v were specified.

uptime & last reboot

uptime Show how long the system has been running.

last reboot Show when the last reboot was.

hostname

hostname Set or print the name of the current host system.

hostname -i Display all local IP addresses of the host system.

date & cal & timedatectl

date Display or set date and time.

cal Displays a calendar.

timedatectl May be used to query and change the system clock and its settings, and enable or disable time synchronization services.

whereis & which & whatis

whereis Checks the standard binary, and manual page directories for the specified programs, printing out the paths of any it finds.

which Locate a program file in the user’s path.

whatis Display online manual documentation pages.

whoami & finger

whoami Display effective user id.

finger All logged in users information lookup program.

finger [username] Show specific user information.

df & free

df Display free disk space.

free Memory allocation.