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The hard limit of the number of open files is set to 1024 on my machine.

  • I changed /etc/security/limits.conf and added 'idror hard nofile 65000'.
  • In my shell I tried ulimit -n 65000. I get 'ulimit: value exceeds hard limit'
  • In my shell I tried ulimit -Hn 65000. I get 'ulimit: can't raise hard limits'

So how can I increase the setting for the limit of open files without reboot?

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After a limits.conf change, you need to log out and back in. – David Schwartz Nov 15 '12 at 0:57

You can just change it as root. For example:

$ ulimit -n  
$ ulimit -n 8192
bash: ulimit: open files: cannot modify limit: Operation not permitted
$ sudo bash                    
# ulimit -n                    
# ulimit -n 8192                  
# su - normaluser                 
$ ulimit -n                       
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