View source for Preventing Your Programs From Overrunning Our Computers

==INTRO==

:As part of being a Computer Science student, you will no doubt create and run your own programs on our [https://support.cs.jhu.edu/wiki/Category:Linux_Clients CS Linux Systems]   You also might be downloading programs from elsewhere and running then on our systems as well.

:It's possible that software you write (or software you've downloaded and run) could, when running, exceed the existing resources on our systems.

==Computing System Resources That Could Be Exceeded==

* Memory (RAM)

* CPU (processing power)

* Disk space
** ''Ugrad Net'' users have a [https://support.cs.jhu.edu/wiki/Disk_Quotas disk quota ]  to prevent that.
** ''Grad/Research Net'' users do not have specific disk quotas but must realize that they  share their disk space with faculty, staff, etc. So, they must pay close attention to the disk space they use.
** Disk space not only included your home directory, but can also include your use of the Linux systems's '''/tmp''' directory as well.

==Typical Symptoms Of Exceeding Computer Resources On Our Linux Systems==

* Timeouts ssh'ing into the computer.

* Programs run ''much'' slower than usual

* Programs stop running because they run out of RAM or swap disk space.

==Who Is Affected When Your Program Uses Up Resources On One Of Our Linux Systems?==

:<span style="color:#ff0000">Because all our our CS Linux computers are '''multiuser''' systems, programs that exceed the computer's resources, slowing down the system, could potentially affect '''''all''''' the users logged into those systems, remotely, or at the actual computer console.</span>

:Exceeding the computer's resources could also affect programs running in the background, perhaps as part of the computer's own system software or other users' batch jobs.   

:'''''So... always be aware that you are not necessarily the only one logged into a system when you're running your own programs.'''''

==Tips To Prevent Your Programs From Exceeding The System Resources On Our Computers==

*  Try to design your programs and/or datasets so that their running memory requirements don't exceed the capabilities of the system they're running on.  Therefore, become familiar with the specs of our CS Linux systems:
** [https://support.cs.jhu.edu/wiki/Linux_Clients_on_the_CS_Grad/Research_Net Specs on our Grad/Research Net Linux Computers ]
** [https://support.cs.jhu.edu/wiki/Linux_Clients_on_the_CS_Undergrad_Net Specs on our Ugrad Net Linux Computers]

* Try to avoid using the system's complete RAM memory as much as possible.  Put safeguards into your programs to monitor your use of memory.

* Try to run your programs during low-demand times of day (mornings are best; late evenings are the most busy.)

* Try not to tie up the computer's resources for longer than the program needs to run.

:: '''Do not forget that you are running programs.'''  One of the biggest areas we've had issues with is that some users start their programs in the background and forget that the programs are still running. And in some cases, the programs have issues and start using more resources than actually needed.  

::'''Therefore... ''please make sure you check in on your running programs often, and use monitoring tools to make sure you are not exceeding resources.'''''

==Monitoring Your Processes' Memory and CPU Usage With Linux Commands==
:Use the '''top''' or '''htop''' programs to see your program's stats.
:* '''top'''
:** top -u ''username''
:* '''htop'''
:** htop -u ''username''
:** htop --user=''username''
:* '''ps''' (coming soon)

==Ending Or Modifying Your Running Process Using Linux Commands==

===Ending A Process===
:* '''kill''' - end a process
:** First, determine process ID (PID)
:** Generally best to choose the ___ [https://www.tecmint.com/how-to-kill-a-process-in-linux kill signal]
:***  Example: Kill process with PID 15476 using kill signal _____: 
:**** ''kill -____ 15476''
:* '''pkill''' - end a process
:** First, determine process ID (PID)
:** Determine appropropriate [https://www.tecmint.com/how-to-kill-a-process-in-linux kill signal]
:***Example: to kill all processes owned by you (with your username being ''csstar'')
:****'''pkill -9 -u ''csstar'''''  (this example will also kill your logged-in shell process.)
:* Within '''top''' command
:** Find desired process ID (PID)
:** press ''k'' (for ''kill'')
:** enter PID at prompt.
:** enter [https://www.tecmint.com/how-to-kill-a-process-in-linux kill signal]

===Modifying A Process's Running Priority===
:* '''nice''' - modify a process's running priority

==And, Worth Mentioning Again...==
: Please remember that because these are multiuser systems,  ''other users could be logged into the system and could be affected if your running program exceeds the computer's resources.''