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6.2 Lab - Not seeing any difference after changing kernel.pid_max

Posts: 20
in LFS201 Class Forum - Discontinued

I'm not seeing any difference after changing kernel.pid_max. Am I doing something wrong?

[sfox@localhost ~]$ sysctl kernel.pid_max
kernel.pid_max = 24000
[sfox@localhost ~]$ cat /proc/sys/kernel/pid_max
24000
[sfox@localhost ~]$ cat &
[4] 2127

[4]+ Stopped cat
[sfox@localhost ~]$ kill -9 2127
[4]+ Killed cat
[sfox@localhost ~]$ sudo sysctl kernel.pid_max=10000
[sudo] password for sfox:
kernel.pid_max = 10000
[sfox@localhost ~]$ sudo su
[root@localhost sfox]# echo 10000 > /proc/sys/kernel/pid_max
[root@localhost sfox]# cat $_
cat: 10000: No such file or directory
[root@localhost sfox]# cat /proc/sys/kernel/pid_max
10000
[root@localhost sfox]# cat &
[1] 2222
[root@localhost sfox]# kill -9 2222
[1]+ Killed cat
[root@localhost sfox]#

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Comments

  • Posts: 916
    On some systems (which I haven't seen for a long time) you have to do
    systctl -w pid_max=12000
    or whatever, where the -w is for write. What distro is this?
    I think technically the -w is required but ignored by most installations.
    Read the man page for sysctl
  • Posts: 25
    Hi ultraninja,

    I think the reason you didn't see any difference after changing pid_max is because you didn't change it to a value less than the PID of your first cat process. That is, you changed pid_max to 10000 but the PID of the first cat process was 2127. If you had changed pid_max to 2000, I think you would then see the PIDs roll over to 300 again.

    Thanks,

    Adam
  • Posts: 20
    Thanks for that tip Adam. It worked perfectly. Though I set pid_max to 10000 again, it was lower than the pid of cat so the next cat started at 378. Excellent! How are you enjoying the course?
    1. [sfox@localhost ~]$ sudo sysctl kernel.pid_max
    2. [sudo] password for sfox: 
    3. kernel.pid_max = 32768
    4. [sfox@localhost ~]$ cat &
    5. [1] 20081
    6.  
    7. [1]+  Stopped                 cat
    8. [sfox@localhost ~]$ kill -9 20081
    9. [1]+  Killed                  cat
    10. [sfox@localhost ~]$ sudo sysctl kernel.pid_max=10000
    11. kernel.pid_max = 10000
    12. [sfox@localhost ~]$ sudo su
    13. [root@localhost sfox]# echo 10000 > /proc/sys/kernel/pid_max
    14. [root@localhost sfox]# cat /proc/sys/kernel/pid_max 
    15. 10000
    16. [root@localhost sfox]# exit
    17. exit
    18. [sfox@localhost ~]$ cat &
    19. [1] 378
    20.  
    21. [1]+  Stopped                 cat
    22. [sfox@localhost ~]$
    23.  
  • Posts: 25
    I thought the course was good and I learnt a lot. I went through everything twice before doing a third pass on only the parts relevant to the LFCS. I'm going to do a fourth pass on the parts that are relevant to the LFCE as a way of getting started on preparing for that exam.

    Thanks,

    Adam
  • Posts: 20
    Hopefully 4 passes should do it :P

    I haven't worked out a strategy yet, I was just going to work through all the materials and labs then see how confident I felt. Maybe do a few passes.
  • Posts: 25
    Three passes did it to get my LFCS :-). And the third pass was really focused on just those sections of the course that would be on the exam. In retrospect it was worth it. I was able to perform a lot of the tasks by instinct. If I had to stop to think about the process and look up the details I'm sure I would have run out of time. As it was, there were a couple of questions I had to skip over and didn't have time to get back to.

    Thanks,

    Adam

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