ulimit or files-max?

[Alex]

Hi, what is the current way to increase the number of available open files?
This is for a mariadb database server I'm trying to configure based on
instructions from the database developer to increase the total number of
files to 50000. I've added the following to /etc/security/limits.conf and
rebooted:

root            -       nofile          50000

ulimit -n as root now shows:
# ulimit -n
50000

Can this value also be set by using sysctl and setting fs.file-max to 50000?
# sysctl -a|grep file
fs.file-max = 50000
fs.file-nr = 6864       0       50000
fs.xfs.filestream_centisecs = 3000

Which is the correct way? Also, does fs.file-nr mean there are currently
6864 open files on the system?

[Roger Heflin]

Either way works.

Yes, file.files.nr first column is the current number in use.

Also note that systemd used to not load the limits.conf file and as
such may have its own lower limits on anything started under a systemd
service.   I think the theory was anything started under systemd
should provide any override limits, and that the low defaults were
intended to limit the ability of something to overrun the system.

Note this:
 cat /proc/3733/limits

will show you the active limits on pid 3733 so find the pid for
mariadb and its children and see what their actual limit is.

On Mon, Nov 13, 2023 at 3:50 PM Alex  wrote:
> Hi, what is the current way to increase the number of available open files? This is for a mariadb database server I'm trying to configure based on instructions from the database developer to increase the total number of files to 50000. I've added the following to /etc/security/limits.conf and rebooted:
>
> root            -       nofile          50000
>
> ulimit -n as root now shows:
> # ulimit -n
> 50000
>
> Can this value also be set by using sysctl and setting fs.file-max to 50000?
> # sysctl -a|grep file
> fs.file-max = 50000
> fs.file-nr = 6864       0       50000
> fs.xfs.filestream_centisecs = 3000
>
> Which is the correct way? Also, does fs.file-nr mean there are currently 6864 open files on the system?
>
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[Samuel Sieb]

On 11/13/23 13:48, Alex wrote:
> Hi, what is the current way to increase the number of available open 
> files? This is for a mariadb database server I'm trying to configure 
> based on instructions from the database developer to increase the total 
> number of files to 50000. I've added the following to 
> /etc/security/limits.conf and rebooted:
>
> root            -       nofile          50000
>
> ulimit -n as root now shows:
> # ulimit -n
> 50000

As mentioned, this only applies to the root use while logged in, not 
services.
> Can this value also be set by using sysctl and setting fs.file-max to 50000?
> # sysctl -a|grep file
> fs.file-max = 50000
> fs.file-nr = 6864       0       50000
> fs.xfs.filestream_centisecs = 3000

The default value here is:
# sysctl -a | grep file
fs.file-max = 9223372036854775807

I think that is the maximum for the entire system, so you probably don't 
want to limit that.

Checking a couple of services, I see that postgresql has
Max open files            1024                 524288 
files
and postfix has
Max open files            524288               524288 
files
I assume that postfix has adjusted it's own soft limit as mentioned in 
another email.

So the answer to the question in the subject is neither.  If the service 
doesn't adjust the limit itself, then you'll need to add an override 
option for the service file.

As an aside, while doing this investigation I discovered that my desktop 
has:
fs.file-nr = 45472	0	9223372036854775807
so I'm going to do some poking around to find out what is opening so 
many files.