File descriptor

Global limit

# cat /proc/sys/fs/file-max

File: /etc/sysctl.conf

fs.file-max = 65536

Apply the changes made in sysctl.conf.

# sysctl -p

# ulimit -n

File: /etc/security/limits.conf

username         soft    nofile          4096
username         hard    nofile          16384

Instead of username you can also use * as a wildcard.

The soft limit is the value a user starts with after login and the hard limit is the value a user is allowed to raise the value to.

Changes can be made with

$ ulimit -n 8192

Note: For users this gets applied at login via pam_limits.so. When running a daemon it may have to set this by its own.