Linux Process Management Concepts
The process with ID 0 is the swapper (or sched), the process responsible with paging. It is part of the kernel, rather than user-space.
The process with ID 1 is the init process, and it is responsible with starting and shutting down the system.
The number of threads for process can be read from the process' corresponding /proc/<pid>/status, as described here: "Threads:".
Maximum Number of Processes Allowed on the System
To get the actual number of processes present in the system, see /proc/stat.
Maximum Number of Processes Available to a Single User
The current value can be read and set with ulimit -u.For Java applications, this setting limits the number of threads a JVM can create, and it can cause the JVM to throw "java.lang.OutOfMemoryError: unable to create new native thread" exceptions when that limit is reached. For more details see
The O/S level symptom of reaching the per-user process limit is:
-bash: fork: retry: Resource temporarily unavailable
while trying to execute an arbitrary process.