Operation of calculations

General information

This text regulates the conditions under which it is possible to run processes on generally available shared faculty machines that are more demanding on system resources (memory, CPU, disk operations, etc.) or are of a longer-term nature, etc.

When starting such processes, it is generally necessary to make sure that you do not have exclusive access to the faculty machines and that they can also be used by other users. Therefore, it is necessary to run such processes with care, especially so as not to restrict interacting users. This can be achieved by following the instructions below.

For larger calculations (duration in the order of days, more machines, CPU intensive) it is also necessary to report them with a brief justification and duration to the address unix@fi.muni.cz .

You do not need to follow these instructions for non-repetitive short-term processes or interactive debugging of your programs. Also performing calculations on Aura works in another mode and not all restrictions described here apply.

The administrators of the faculty machines continuously monitor the use of the machines. In case of notification to the administrator, it is necessary to reduce the generated load. Processes that are not reported or overload the machine (s) may be terminated without notice. Also, in the event of repeated or more serious non-compliance with the instructions provided here, administrators may temporarily suspend the account.

Restrictive measures

On classroom machines that are used directly in teaching (Nymfe23–74 and sometimes Luna01–12), it is undesirable to run calculations at the time of teaching or potential exams, ie generally between 07: 45–20: 15. In general, however, it is best to run calculations only at night, if possible.

If the calculations are of a longer-term nature and are part of the research, resp. final work, it is advisable to use a computer server Aura designed for this. If you do not have access to it, you can request it to be assigned at unix@fi.muni.cz .

For CPU-intensive processes, you need to set the lowest priority to +19, for example with the command nice :

nice -n +19 ./program

It is also possible to restrict the running of process threads only to specified CPU cores with the command taskset :

taskset -c 1-2,4 ./program

If the running process generates a higher I / O load (disk access, large transfers), it is advisable to place files with such access in a folder on the local disk ( /tmp ), not to the home directory ( /home/xlogin ), as it is available over the network via NFS and the volume on which the data is located is also used by other machines.

You can use the command to limit the amount of memory used by processes running from a single shell instance when running more memory-intensive calculations ulimit -v as a prevention against memory depletion or overuse. You can also set a limit on the time consumed by a process using the command ulimit -t ; when the limit is exceeded, the process will be terminated by a KILL signal. The command will provide more information about it and its other options help ulimit or system call documentation setrlimit .

Load monitoring

During the calculations, it is appropriate to continuously monitor the status, resp. machine load (disk full, memory, I / O, load, process status), which is used for example by the following tools:

• top, htop - summary information on the system and the processes in it
• ps ux - a listing of information about my processes
• iostat - list of information about I / O operations
• who - list of registered users (relevant only for machines in classrooms and halls)
• df - utilizing the capacity of disk volumes