Updated File Descriptors (markdown)

File-Descriptors.md

@@ -1 +1,23 @@
-TODO
+## File Descriptor Limit
+
+Linux kernel has fairly low default limit of [file descriptors](https://en.wikipedia.org/wiki/File_descriptor) that a given process can open - only 4096. Games can use a lot of them for inter-process communication, synchronization primitives and reading assets.
+
+Setting this limit higher is necessary to be able to run a lot of the games out there.
+
+## Systemd-based Linux Distributions
+
+Systemd 240 or newer by default sets the soft limit to 1024 and hard limit to 524288. No action is necessary.
+
+If you want to further alter those values see `DefaultLimitNOFILE` in [`man systemd.conf.d`](https://www.freedesktop.org/software/systemd/man/systemd-system.conf#DefaultLimitCPU=).
+
+## Non-Systemd Linux Distributions With PAM
+
+If your distribution is using [PAM](https://github.com/linux-pam/linux-pam) and has `pam_limits.so` enabled you can configure the limits via [`limits.conf`](https://www.man7.org/linux/man-pages/man5/limits.conf.5.html), e.g `/etc/security/limits.conf`.
+
+```
+*               hard    nofile             524288
+```
+
+## Everything Else
+
+Please consult documentation of your distributions.