Sage Math freeze my Linux on intensive computation.

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This is a linux question. Short answer: use nice and/or renice.

Longer answer. On my machine there are the following sage related processes right now:

$ ps -ef | fgrep sage
dan       5450  5429  0 22:04 pts/7    00:00:00 grep -F --color=auto sage
dan      31748 12728  0 Nov26 pts/5    00:00:30 python2 /usr/bin/sage-ipython -i
dan      32751 31748  0 Nov26 pts/5    00:00:03 python2 /usr/bin/sage-cleaner

In top -u dan (top processes for the user named dan) there are two relevant columns PR and NI, priority and nice value. (One can scroll down and later come back in the top terminal menu by using PageDown and PageUp.) The nice value tells how "gentle" is a process w.r.t. the other processes. (A good nice value for a process means, it opens wide the door and lets first the ladies go through, also the friends, and the seniors, even also the kids in hurry to start that action games of intelligent destruction, well they all, the ladies, the friends, the seniors, even the kids will say "what a nice process!" - and now it is really hard to forget why they call it "nice value".)

The process identity, as delivered from ps -ef and / or top can be used from the terminal line to give more or less "voice" to a process. For instance:

nice -n 17 sage

starts sage (in the same terminal) with the -niceness value 17. In the top of the user dan i found among many other lines:

PID USER      PR  NI    VIRT    RES  %CPU %MEM     TIME+ S COMMAND          
 5429 dan       20   0    7,7m   4,0m   0,0  0,1   0:00.04 S          `- bash                    
 6155 dan       37  17  807,0m 170,3m   0,0  5,4   0:02.33 S              `- python2             
 6175 dan       37  17    0,0m   0,0m   0,0  0,0   0:00.02 Z                  `- python2         
 5976 dan       20   0    7,7m   4,0m   0,0  0,1   0:00.00 S          `- bash                    
 6096 dan       20   0    9,0m   3,7m   1,3  0,1   0:03.18 R              `- top                 
 6048 dan       20   0    7,7m   3,9m   0,0  0,1   0:00.03 S          `- bash                    
16226 dan       20   0  208,0m   8,0m   0,0  0,3   0:01.83 S      `- xfce4-appfinder

The column NI gives the niceness.

The related ps information:

$ ps -lu dan | fgrep python
0 S  1000  6155  5429  0  97  17 - 206636 poll_s pts/7   00:00:02 python2
0 Z  1000  6175  6155  0  97  17 -     0 -      pts/7    00:00:00 python2 <defunct>

Let us reset the niceness to 9. I tried:

$ renice -n 9 -p 6155
renice: failed to set priority for 6155 (process ID): Permission denied

$ sudo renice -n 9 -p 6155
[sudo] password for dan: 
6155 (process ID) old priority 17, new priority 9

Well, the higher rights could set the priority of the process. Let's check:

$ ps -lp 6155 6175
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY        TIME CMD
0 S  1000  6155  5429  0  89   9 - 206636 poll_s pts/7     0:02 python2 /usr/bin/sage-ipython -i
0 Z  1000  6175  6155  0  97  17 -     0 -      pts/7      0:00 [python2] <defunct>

It is maybe better to start sage with the right niceness. Note that the default niceness is

$ nice
0

You could have a look at the nice (for processor) and ulimit (for RAM) shell commands.