Maximum value for /proc/sys/fs/file-max

Question

Today my server crashed with Too many open files in system: but I already have high values, what is a maximum value for this?

I feel like there aren't good results on google for this, explaining what needs to be taken in consideration for setting those values, they just say to set it to like 100k.

I have a 32 GB RAM server using only 10 GB right now, I assume increasing the file limits to very high values will increase RAM usage, is there some kind of formula you can use to calculate this? Like for 8 GB of ram you can have X number of files open?

Current settings:

cat /proc/sys/fs/file-max
100000
ulimit -Hn
1048576
ulimit -Sn
1024

Answer 1

As Kusalananda says, increasing file-max won’t directly have an impact on memory use, but it will allow processes to open more file descriptors which will have a knock-on effect (both from tracking file descriptions in the kernel, and increased memory usage in the processes using those descriptions and descriptors) — the kernel comments suggest approximately one kilobyte per file for the kernel’s data, and will reduce the default value of file-max (8192) if that ends up representing more than 10% of memory when the system boots (i.e. there’s only 80 MiB of RAM). The maximum value imposed by the kernel is the maximum value which can be stored in a variable of type long in C on your architecture.

If you increase file-max, you should also increase inode-max; the kernel documentation says this should be “3-4 times larger than the value in file-max, since stdin, stdout and network sockets also need an inode struct to handle them.”

Note that hitting file-max will result in a kernel log message saying “VFS: file-max limit n reached”, with the appropriate value for n. If you don’t have that in your logs, you’re either not hitting file-max, or filtering your logs too much (it’s an info-level log message).

(file-max doesn’t limit processes with CAP_SYS_ADMIN, so hitting it won’t stop everything.)