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Root Cause There can be various reasons for processes not being able to fork: There is a misbehaving service or process running, consuming more resources than expected. The system was not able to create new processes, because of the limits set for nproc in /etc/security/limits.
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 indi- cate the error.
This is commonly caused by running out of file descriptors.
There is the systems total file descriptor limit, what do you get from the command:
sysctl fs.file-nr
This returns counts of file descriptors:
<in_use> <unused_but_allocated> <maximum>
To find out what a users file descriptor limit is run the commands:
sudo su - <username>
ulimit -Hn
To find out how many file descriptors are in use by a user run the command:
sudo lsof -u <username> 2>/dev/null | wc -l
So now if you are having a system file descriptor limit issue you will need to edit your /etc/sysctl.conf file and add, or modify it it already exists, a line with fs.file-max and set it to a value large enough to deal with the number of file descriptors you need and reboot.
fs.file-max = 204708
Another possibility is too many threads. We just ran into this error message when running a test harness against an app that uses a thread pool. We used
watch -n 5 -d "ps -eL <java_pid> | wc -l"
to watch the ongoing count of Linux native threads running within the given Java process ID. After this hit about 1,000 (for us--YMMV), we started getting the error message you mention.
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