• hostname 
Print the name of the local host (the machine on which you are working). Use netconf (as root) to change the name of the machine. 

• whoami 
Print my login name. 

• id username 
Print user id (uid) and his/her group id (gid), effective id (if different than the real id) and the supplementary groups. 

• date 
Print or change the operating system date and time. E.g., I could change the date and time to 2000-12-31 23:57 using this command: 
date 123123572000 
To set the hardware (BIOS) clock from the system (Linux) clock, use the command (as root) setclock 

• time 
Determine the amount of time that it takes for a process to complete + other info. Don't confuse it with the date command. E.g. I can find out how long it takes to display a directory content using: 
time ls 

• who 
Determine the users logged on the machine. 

• rwho -a 
(=remote who) Determine all users logged on your network. The rwho service must be enabled for this command to run. If it isn't, run setup as root to enable "rwho". 

• finger user_name 
System info about a user. Try: finger root 

• last 
Show listing of users last logged-in on your system. 

• history | more 
Show the last (1000 or so) commands executed from the command line on the current account. The "| more" causes the display to stop after each screenful. 

• uptime 
Show the amount of time since the last reboot. 

• ps 
(=print status) List the processes currently run by the current user. 

• ps axu | more 
List all the processes currently running, even those without the controlling terminal, together with the name of the user that owns each process. 

• top 
Keep listing the currently running processes, sorted by cpu usage (top users first). In KDE, you can get GUI-based Ktop from "K"menu under "System"-"Task Manager" (or by executing "ktop" in an X-terminal). 

• uname -a 
(= Unix name with option "all") Info on your (local) server. I can also use guname (in X-window terminal) to display the info more nicely. 

• free 
Memory info (in kilobytes). 

• df -h 
(=disk free) Print disk info about all the filesystems (in human-readable form) 

• du / -bh | more 
(=disk usage) Print detailed disk usage for each subdirectory starting at the "/" (root) directory (in human legible form). 

• cat /proc/cpuinfo 
Cpu info--it show the content of the file cpuinfo. Note that the files in the /proc directory are not real files--they are hooks to look at information available to the kernel. 

• cat /proc/interrupts 
List the interrupts in use. 

• cat /proc/version 
Linux version and other info 

• cat /proc/filesystems 
Show the types of filesystems currently in use. 

• cat /etc/printcap 
Show the setup of printers. 

• lsmod 
(As root. Use /sbin/lsmod to execute this command when you are a non-root user.) Show the kernel modules currently loaded. 

• set|more 
Show the current user environment. 

• echo $PATH 
Show the content of the environment variable "PATH". This command can be used to show other environment variables as well. Use "set" to see the full environment. 

• dmesg | less 
Print kernel messages (the content of the so-called kernel ring buffer). Press "q" to quit "less". Use less /var/log/dmesg  to see what "dmesg" dumped into this file right after the last system bootup. 

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