inotify: ‘too many open files’

inotify is a part of the Linux kernel which can be used to monitors changes to the filesystem. Among other softwares, this interface is used by the file watcher of Deno, a JavaScript runtime used by Quarto. Rendering a large project often leads to the message

Error: Too many open files (os error 24)

This is caused by Deno reaching the limit of /proc/sys/fs/inotify/max_user_instances, which by default is 128.

The limit can be temporarily raised by

echo "1024" | sudo tee /proc/sys/fs/inotify/max_user_instances

and permanently by an entry

fs.inotify.max_user_instances=1024

in /etc/sysctl.conf, the configuration file for the kernel parameter configuration tool sysctl. For the change to take effect immediately,

sudo sysctl -p

is necessary.

sysctl is not related to systemd, but it is controlled by a systemd service systemd-sysctl.service, and therefore

sudo systemctl restart systemd-sysctl.service

can be used instead.