What is rctl

In FreeBSD, in addition to login.conf, we also get a very nice and flexible mechanism for setting resource limits: rctl. I like it in particular for limiting resources allocated to each jail.

Configuration

Here is a short example:

jail:example_jail:vmemoryuse:deny=2G/jail
jail:example_jail:maxproc:deny=200/jail
jail:example_jail:readiops:throttle=500/jail
jail:example_jail:pcpu:deny=70/jail

In the above, for the jail identified by example_jail we allow:

• 2G of memory,
• 200 processes,
• 500 I/O read operations per second,
• 70% of CPU.

Enabling rctl on boot

Actually, there is no need to enable anything in rc.conf – this is what you can find in /etc/defaults/rc.conf:

rctl_enable="YES"               # Load rctl(8) rules on boot
rctl_rules="/etc/rctl.conf"     # rctl(8) ruleset. See rctl.conf(5).

It is sufficent to simply create /etc/rctl.conf and the limits will be set on system boot. However, we need to edit /boot/loader.conf to add:

kern.racct.enable="1"

and then reboot the system.

rctl

• rctl (without any switches) – prints the current set of rules
• rctl -r : – clears all the rules
• rctl -u jail:example_jail – prints the resource utilisation for example_jail