RCTL(8) FreeBSD System Manager's Manual RCTL(8)


rctldisplay and update resource limits database


rctl [ -h][ -n][ filter]

rctl -a [ rule]

rctl -l [ -h][ -n][ filter]

rctl -r [ filter]

rctl -u [ -h][ filter]

rctl requires the kernel to be compiled with:

options RACCT
options RCTL


When called without options, the rctl command writes currently defined RCTL rules to standard output.

If a filter argument is specified, only rules matching the filter are displayed. The options are as follows:

-a rule
Add rule to the RCTL database.
-l filter
Display rules applicable to the process defined by filter. Note that this is different from showing the rules when called without any options, as it shows not just the rules with subject equal to that of process, but also rules for the user, jail, and login class applicable to the process.
-r filter
Remove rules matching filter from the RCTL database.
-u filter
Display resource usage for a subject ( process, user, loginclass or jail) matching the filter.
"Human-readable" output. Use unit suffixes: Byte, Kilobyte, Megabyte, Gigabyte, Terabyte and Petabyte.
Display user IDs numerically rather than converting them to a user name.

Modifying rules affects all currently running and future processes matching the rule.


Syntax for a rule is subject:subject-id:resource:action=amount/per.

defines the kind of entity the rule applies to. It can be either process, user, loginclass, or jail.
identifies the subject. It can be a process ID, user name, numerical user ID, login class name from login.conf(5), or jail name.
identifies the resource the rule controls. See the RESOURCES section below for details.
defines what will happen when a process exceeds the allowed amount. See the ACTIONS section below for details.
defines how much of the resource a process can use before the defined action triggers. Resources which limit bytes may use prefixes from expand_number(3).
defines what entity the amount gets accounted for. For example, rule "loginclass:users:vmem:deny=100M/process" means that each process of any user belonging to login class "users" may allocate up to 100MB of virtual memory. Rule "loginclass:users:vmem:deny=100M/user" would mean that for each user belonging to the login class "users", the sum of virtual memory allocated by all the processes of that user will not exceed 100MB. Rule "loginclass:users:vmem:deny=100M/loginclass" would mean that the sum of virtual memory allocated by all processes of all users belonging to that login class will not exceed 100MB.

A valid rule has all those fields specified, except for per, which defaults to the value of subject.

A filter is a rule for which one of more fields other than per is left empty. For example, a filter that matches every rule could be written as ":::=/", or, in short, ":". A filter that matches all the login classes would be "loginclass:". A filter that matches all defined rules for maxproc resource would be "::maxproc".


subject subject-id
process numerical Process ID
user user name or numerical User ID
loginclass login class from login.conf(5)
jail jail name


cputime CPU time, in seconds
datasize data size, in bytes
stacksize stack size, in bytes
coredumpsize core dump size, in bytes
memoryuse resident set size, in bytes
memorylocked locked memory, in bytes
maxproc number of processes
openfiles file descriptor table size
vmemoryuse address space limit, in bytes
pseudoterminals number of PTYs
swapuse swap usage, in bytes
nthr number of threads
msgqqueued number of queued SysV messages
msgqsize SysV message queue size, in bytes
nmsgq number of SysV message queues
nsem number of SysV semaphores
nsemop number of SysV semaphores modified in a single semop(2) call
nshm number of SysV shared memory segments
shmsize SysV shared memory size, in bytes
wallclock wallclock time, in seconds
pcpu %CPU, in percents of a single CPU core


deny deny the allocation; not supported for cputime and wallclock
log log a warning to the console
devctl send notification to devd(8) using system = "RCTL", subsystem = "rule", type = "matched"
sig* e.g. sigterm; send a signal to the offending process. See signal(3) for a list of supported signals

Not all actions are supported for all resources. Attempting to add a rule with an action not supported by a given resource will result in error.


The rctl utility exits 0 on success, and >0 if an error occurs.


Prevent user "joe" from allocating more than 1GB of virtual memory:
rctl -a user:joe:vmemoryuse:deny=1g

Remove all RCTL rules:

rctl -r :

Display resource usage information for jail named "www":

rctl -hu jail:www

Display all the rules applicable to process with PID 512:

rctl -l process:512

Display all rules:


Display all rules matching user "joe":

rctl user:joe

Display all rules matching login classes:

rctl loginclass:




The rctl command appeared in FreeBSD 9.0.


The rctl was developed by Edward Tomasz Napierala <trasz@FreeBSD.org> under sponsorship from the FreeBSD Foundation.


Limiting memoryuse may kill the machine due to thrashing.
September 11, 2014 FreeBSD