MySQL error #1135: Can’t create a new thread (errno 11).

By Jonesy • Apr 13th, 2006 • Category: Linux, SQL

This error was the bane of my life for a while, and it was very hard to get a definitive answer as to what was causing it, I hope this saves you some trouble.

My website occasionally got large traffic spikes, and at the top of these peaks, I would start to see errors like these:

MySQL error #1135: Can’t create a new thread (errno 11). If you are not out of available memory, you can consult the manual for a possible OS-dependent bug.

I looked in the my.cnf file on the db server and looked at the open files limit, because a process is counted as an open file, but it seemed fine:

[mysqld_safe]
open-files-limit=10240

I also checked that maximum connections was high enough, it was at 2048.

What the open-files-limit in my.cnf files does is it tells the init script to use ulimit to whatever number you put in there.

After a lot of digging around various places, and much frustration, I discovered that by default linux has a hard limit of 1024 open files for all non super-users, so even though I had set a high open-files-limit, it was capped at 1024 by the OS. I also discovered how to raise it;

/etc/security/limits.conf

This file is used by PAM to set things like maximum processes, max open files, memory usage etc and these limits can be set on a per-user basis, so I added these lines:

mysql soft nofile 4096
mysql hard nofile 4096


and restarted MySQL. BAM! That did the trick.
One more thing to make sure of is that the su pam config file (/etc/pam.d/su) is using pam_limits.so, as that is the pam module which enforces limits.

Good luck!
-Jonesy

Related posts:

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Jonesy is currently working for a wireless ISP as Senior Network Operations Engineer. He has several years of experience in Systems Administration and Network Administration and Design, with a particular interest in Linux and IP networking.
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6 Responses »

  1. Jamsi on April 13th, 2006 at 5:26 pm:

    I need me some of this large traffic spike u talk about.

  2. Mark on February 27th, 2007 at 3:08 am:

    Appreciate this posting! I forgot about those pam limits, this is just what I needed, thanks for reminding me. I added (without quotes)

    “session required /lib/security/pam_limits.so”

    to “/etc/pam.d/login”

  3. Dave on March 7th, 2008 at 6:06 am:

    is a simular fix for a win box?
    i have been trying to find a fix for some time, this is the first i see of anything resembling one.

    win box runing server 2003.
    4g ram

    have actually planed to format and change it centos, but it apears the issue is not completly the os.

  4. David on July 19th, 2008 at 2:39 am:

    Question; without the addition of the pam_limits.so to pam.d/login, wouldn’t there effectively be no limits? Or are there always limits by default, you then have to include the pam limits file before you can raise them?

  5. Jonesy on July 28th, 2008 at 3:46 pm:

    You’re absolutely right, David, if you disabled the pam_limits.so module you would have no limits.

  6. Jonesy on July 28th, 2008 at 3:48 pm:

    Dave, I’m afraid this solution is very Linux-specific, the operating system architectures are quite different, and PAM is not present in windows.

    It is _possible_ that windows has similar limits, but I have no idea of how one would go about finding them or raising them (if they exist!)

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