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What is the maximum and minimum value for a PID (Process ID) on Linux and Solaris?

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From http://www.alexxoid.com/blog/linux/getting-the-max-pid-value-for-linux-process.html:

To get the max PID value that can be assigned to Linux process, run the following command:

cat /proc/sys/kernel/pid_max

On most Linux machines, the result is 32768 (= 215).

However, it can be set to any value up to 4194304 (= 222) if necessary. Servers might have a larger limit to avoid PID collisions, for example.

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You've had, and accepted, a Linux answer. On Solaris, the maximum value of a process ID is a kernel tunable parameter — pidmax in /etc/system — that defaults to 30,000 and that can be set anywhere between 266 and 999,999. Note that this is not max_nprocs, which is a kernel tunable parameter with a subtly different function.

  • You mentioned that max_nprocs is different, what's the difference? – ffledgling Mar 14 '17 at 11:52
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    @ffledgling max_nprocs limits the number of concurrent processes, regardless of whether unused pids are available or not. – jlliagre May 18 '18 at 10:26
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The minimum is 1 and usually the maximum is 2^15

  • ... except on Solaris, as in the question, where it isn't. – JdeBP Jun 10 '11 at 14:45
  • The minimum PID is actually 0, i.e. the kernel which isn't a process really ... – jlliagre Jun 10 '11 at 15:05
  • do the kernel get a PID? – Giovanni Tirloni Jun 13 '11 at 9:58
  • It doesn't need one but is given pid 0. Under Linux, I guess it is only shown as a PPID but under Solaris, there is definitely a /proc/0 entry and ps reports process 0 as "sched". – jlliagre Jun 14 '11 at 5:32
  • @jlliagre ubuntu has no /proc/0 neither ps -p 0 works :), anyway, as a variable pid initializer, the best seems to be -1 – Aquarius Power Apr 17 '16 at 21:36

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