List the users logged in on the machine. —
List all users logged in on your network. The rwho service must be enabled for this command to work.
System info about a user. Try: finger root last. This lists the 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 screen fill.
Print working directory, i.e. display the name of your current directory on the screen.
Print the name of the local host (the machine on which you are working).
Print your login name.
Print user id (uid) and his/her group id (gid), effective id (if different than the real id) and the supplementary groups.
Print or change the operating system date and time. E.g., change the date and time to 2000-12-31 23:57 using this command
To set the hardware clock from the system clock, use the command (as root)
Determine the amount of time that it takes for a process to complete+ other info. Don’t confuse it with date command. For e.g. we can find out how long it takes to display a directory content using time ls
Amount of time since the last reboot
List the processes that are have been run by the current user.
ps aux | more
List all the processes currently running, even those without the controlling terminal, together with the name of the user that owns each process.
Keep listing the currently running processes, sorted by cpu usage (top users first).
Info on your server.
Memory info (in kilobytes).
Print disk info about all the file systems in a human-readable form.
du / -bh | more
Print detailed disk usage for each subdirectory starting at root (in a human readable form).
(as root. Use /sbin/lsmod to execute this command when you are a non-root user.) Show the kernel modules currently loaded.
Show the current user environment.
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 current content of the so-called kernel ring buffer). Press q to quit less. Use less /var/log/dmesg to see what dmesg dumped into the file right after bootup. – only works on dedciated systems
Commands for Process control
Display the list of currently running processes with their process IDs (PID) numbers. Use ps aux to see all processes currently running on your system (also those of other users or without a controlling terminal),
each with the name of the owner. Use top to keep listing the processes currently running.
PID Bring a background or stopped process to the foreground.
PID Send the process to the background. This is the opposite of fg. The same can be accomplished with
Run any command in the background (the symbol ‘&’ means run the command in the background?).
Force a process shutdown. First determine the PID of the process to kill using ps.
killall -9 program_name
Kill program(s) by name.
(in an xwindow terminal) Kill a GUI-based program with mouse. (Point with your mouse cursor at the window of the process you want to kill and click.)
(as root) Check and control the printer(s). Type ??? to see the list of available commands.
Show the content of the printer queue.
Remove a printing job job_number from the queue.
Run program_name adjusting its priority. Since the priority is not specified in this example, it will be adjusted by 10 (the process will run slower), from the default value (usually 0). The lower the number (of niceness to other users on the system), the higher the priority. The priority value may be in the range -20 to 19. Only root may specify negative values. Use top to display the priorities of the running processes.
renice -1 PID
(as root) Change the priority of a running process to -1. Normal users can only adjust processes they own, and only up from the current value (make them run slower).