linux - fork: retry: Resource temporarily unavailable
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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

