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A caution on modifying kern.maxfiles values UNIX
I had a devastating experience this morning. On an unrelated issue, I have been hitting up against a max files limit on one of my servers. I noticed that setting ulimit -n unlimited only set it to 12288. I also noticed that in sysctl, the kern.maxfiles value was set to 12288. So, I decided to be smart and try:
sysctl -w kern.maxfiles=unlimited
I got this as response:
kern.maxfiles 12288 -> 0
So, thinking zero means unlimited (because that is the way it is with some applications!), I ran:
ulimit -n unlimited
Unfortunately, this promptly set my open files limit to zero! Immediately, apps stopped running. I continued to have a session, but I couldn't do anything at all. I couldn't set sysctl back; I couldn't reboot; I couldn't do anything. And since the server is 3,000 miles away from me in Phoenix, I had to call and pay for it to be rebooted by hitting the reset button. (Yes, I know, we need a remote reboot switch.)

So, whatever you do, don't set kern.maxfiles=unlimited!
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sysctl doesn't understand "unlimited"
Authored by: hayne on Sep 07, '05 11:34:46AM

I looked at the source code for the 'sysctl' utility and it seems that it does not do anything special with the string "unlimited" - i.e. it does not understand that as a valid value at all.
In fact, if you supply any string that doesn't start with an integer when you are using the "-w" to set an integer parameter value, it will result in the parameter getting set to zero. This is a consequence of bad error handling in the 'sysctl' utility. If you give it a string like "xyz" or anything other than an integer, it will effectively take it as zero.
I have reported this bug to Apple.

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