"Maxuproc parameter and number of processes"

Post #303033580 by Don Cragun on Monday 8th of April 2019 03:30:15 PM

Without digging into the system's header files, you should be able to retrieve your current system's allowed number of processes per user with the command:
Code:
getconf CHILD_MAX

which is defined to return the system's current value for the maximum number of simultaneous processes per real user ID. Note that this says nothing about the size of the kernel's process table which must contain one slot for each process that is currently active. Note that in this case, active means has been started and its exit status has not yet been collected by its parent (or if its parent has died, collected by the system's garbage collector [a process named init on some systems]).

In the old days, the size of the process table was fixed when the kernel was built. Most of today's systems attempt to grow the pricess table as needed rather than failing fork()s when the process table fills up. But, if the kernel runs out of memory, a normal user's fork() will fail and a super-user's fork() may kill off a normal user's running process to allow the super-user to create a new process. What actually happens in these cases varies considerably from system to system.

Last edited by Don Cragun; 04-09-2019 at 12:15 AM.. Reason: Fix typo: s/systems/system's/
 
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FORK(2) 							System Calls Manual							   FORK(2)

NAME
fork - create a new process SYNOPSIS
pid = fork() int pid; DESCRIPTION
Fork causes creation of a new process. The new process (child process) is an exact copy of the calling process except for the following: The child process has a unique process ID. The child process has a different parent process ID (i.e., the process ID of the parent process). The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that, for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the child process can affect a subsequent read or write by the parent. This descriptor copying is also used by the shell to establish standard input and output for newly created processes as well as to set up pipes. The child processes resource utilizations are set to 0; see setrlimit(2). RETURN VALUE
Upon successful completion, fork returns a value of 0 to the child process and returns the process ID of the child process to the parent process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to indicate the error. ERRORS
Fork will fail and no child process will be created if one or more of the following are true: [EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration- dependent. [EAGAIN] The system-imposed limit MAXUPRC (<sys/param.h>) on the total number of processes under execution by a single user would be exceeded. [ENOMEM] There is insufficient swap space for the new process. SEE ALSO
execve(2), wait(2) 3rd Berkeley Distribution May 22, 1986 FORK(2)

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